--- title: "Monitoring & Reliability Glossary | FourSight" description: "Plain-English definitions of uptime, SLA, TLS, DNS, webhook, and incident-response terms — each cited from IETF, NIST, Google SRE, Stripe, AWS, and other primary sources." lang: en json-ld: | { "@context": "https://schema.org", "@type": "DefinedTermSet", "name": "FourSight Monitoring & Reliability Glossary", "description": "Plain-English definitions of monitoring, reliability, security, and SaaS billing terms, each cited from primary authoritative sources.", "url": "https://foursight.cloud/glossary", "hasDefinedTerm": [ { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/uptime", "name": "Uptime", "description": "The percentage of time a service is reachable and responding correctly over a given window. Usually expressed as a number of nines — 99.9% (\"three nines\") allows about 43 minutes of downtime per month.", "url": "https://foursight.cloud/glossary/uptime", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "uptime", "sameAs": [ "https://sre.google/sre-book/service-level-objectives/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/downtime", "name": "Downtime", "description": "Any period during which a service fails to respond, returns errors, or is so degraded it is unusable. Industry practice typically counts hard failures (5xx, timeouts, connection refused) and responses above a defined latency threshold.", "url": "https://foursight.cloud/glossary/downtime", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "downtime", "sameAs": [ "https://sre.google/sre-book/embracing-risk/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/sla", "name": "SLA (Service Level Agreement)", "description": "A formal contract between a service provider and a customer that defines minimum service levels and the consequences (usually credits) if those levels are not met.", "url": "https://foursight.cloud/glossary/sla", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "sla", "sameAs": [ "https://sre.google/sre-book/service-level-objectives/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/slo", "name": "SLO (Service Level Objective)", "description": "An internal reliability target — for example, \"99.9% of API requests succeed within 500 ms over a rolling 30-day window.\" SLOs are stricter than SLAs and used to drive engineering decisions.", "url": "https://foursight.cloud/glossary/slo", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "slo", "sameAs": [ "https://sre.google/sre-book/service-level-objectives/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/sli", "name": "SLI (Service Level Indicator)", "description": "The raw measurement that an SLO is calculated from — request success ratio, latency percentile, or freshness of a data pipeline.", "url": "https://foursight.cloud/glossary/sli", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "sli", "sameAs": [ "https://sre.google/workbook/implementing-slos/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/mttr", "name": "MTTR (Mean Time To Resolve / Recover)", "description": "Average time between an incident being detected and the service being fully restored. Lower MTTR is a primary goal of incident response.", "url": "https://foursight.cloud/glossary/mttr", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "mttr", "sameAs": [ "https://www.atlassian.com/incident-management/kpis/common-metrics" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/mttd", "name": "MTTD (Mean Time To Detect)", "description": "Average time between the start of an incident and the moment your team is first alerted. Fast MTTD depends on dense monitoring and high-signal alerting.", "url": "https://foursight.cloud/glossary/mttd", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "mttd", "sameAs": [ "https://www.atlassian.com/incident-management/kpis/common-metrics" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/mtbf", "name": "MTBF (Mean Time Between Failures)", "description": "Average time a system runs successfully between failures. Higher MTBF indicates a more reliable system.", "url": "https://foursight.cloud/glossary/mtbf", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "mtbf", "sameAs": [ "https://csrc.nist.gov/glossary/term/mean_time_to_failure" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/availability-vs-reliability", "name": "Availability vs Reliability", "description": "Availability measures whether a service responds (uptime %). Reliability measures whether it responds correctly and within acceptable latency. A service can be available but unreliable if responses are slow or wrong.", "url": "https://foursight.cloud/glossary/availability-vs-reliability", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "availability-vs-reliability", "sameAs": [ "https://sre.google/sre-book/embracing-risk/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/latency", "name": "Latency", "description": "The time between sending a request and receiving the first byte of a response, usually measured in milliseconds.", "url": "https://foursight.cloud/glossary/latency", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "latency", "sameAs": [ "https://developer.mozilla.org/en-US/docs/Web/Performance/Understanding_latency" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/percentile-latency", "name": "P50 / P95 / P99 Latency", "description": "Percentile measurements of response time. P95 = 95% of requests complete in this time or faster. P99 captures the slow tail that average latency hides — often where the worst user experiences live.", "url": "https://foursight.cloud/glossary/percentile-latency", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "percentile-latency", "sameAs": [ "https://sre.google/sre-book/monitoring-distributed-systems/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/quorum-monitoring", "name": "Quorum-based Monitoring", "description": "A monitoring technique where a failure is only declared when a majority of independent probes (e.g. 3 of 4 global regions) agree the target is down. Filters out single-region network blips.", "url": "https://foursight.cloud/glossary/quorum-monitoring", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "quorum-monitoring", "sameAs": [ "https://en.wikipedia.org/wiki/Quorum_(distributed_computing)" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/multi-region-monitoring", "name": "Multi-Region Monitoring", "description": "Checking an endpoint from probes located in different geographic regions and networks. Catches regional outages, CDN routing issues, and ISP-specific failures that single-region monitors miss.", "url": "https://foursight.cloud/glossary/multi-region-monitoring", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "multi-region-monitoring", "sameAs": [ "https://sre.google/sre-book/monitoring-distributed-systems/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/probe", "name": "Probe / Probe Node", "description": "A server, hosted in a specific region, that issues monitoring checks against your endpoints on a schedule and reports the results.", "url": "https://foursight.cloud/glossary/probe", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "probe", "sameAs": [ "https://sre.google/workbook/alerting-on-slos/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/synthetic-monitoring", "name": "Synthetic Monitoring", "description": "Active monitoring that simulates user interactions (HTTP requests, browser flows) at a regular interval — as opposed to passive monitoring which observes real user traffic.", "url": "https://foursight.cloud/glossary/synthetic-monitoring", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "synthetic-monitoring", "sameAs": [ "https://cloud.google.com/monitoring/uptime-checks/introduction" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/heartbeat-monitor", "name": "Heartbeat Monitor", "description": "A monitor that expects your job, script, or worker to ping it on a schedule. If the expected ping doesn't arrive within a grace period, the monitor alerts — catching silent failures.", "url": "https://foursight.cloud/glossary/heartbeat-monitor", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "heartbeat-monitor", "sameAs": [ "https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/keyword-monitor", "name": "Keyword Monitor", "description": "An HTTP monitor that not only checks status code but also asserts that the response body contains (or does not contain) a specific string. Catches \"200 OK with wrong content\" failures.", "url": "https://foursight.cloud/glossary/keyword-monitor", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "keyword-monitor", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc9110#name-status-codes" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/http-monitor", "name": "HTTP Monitor", "description": "Sends an HTTP/HTTPS request to a URL and evaluates the response against expected status codes, body content, headers, and latency.", "url": "https://foursight.cloud/glossary/http-monitor", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "http-monitor", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc9110" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/ping-monitor", "name": "Ping Monitor", "description": "Sends ICMP echo requests to a host to confirm it is reachable on the network. Cheap and broadly compatible, but blocked by many cloud providers and firewalls.", "url": "https://foursight.cloud/glossary/ping-monitor", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "ping-monitor", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc792" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/port-monitor", "name": "Port Monitor", "description": "Attempts to open a TCP connection on a specific port (e.g. 25 for SMTP, 5432 for Postgres) to confirm the service is accepting connections.", "url": "https://foursight.cloud/glossary/port-monitor", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "port-monitor", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc9293" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/false-positive", "name": "False Positive", "description": "An alert that fires for a problem that did not actually affect users — usually caused by network blips, probe-side issues, or overly sensitive thresholds. Frequent false positives cause alert fatigue.", "url": "https://foursight.cloud/glossary/false-positive", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "false-positive", "sameAs": [ "https://sre.google/workbook/alerting-on-slos/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/grace-period", "name": "Grace Period", "description": "A buffer window after a missed check or heartbeat before the monitor alerts. Prevents flapping alerts from jobs that occasionally run a few minutes late.", "url": "https://foursight.cloud/glossary/grace-period", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "grace-period", "sameAs": [ "https://sre.google/workbook/alerting-on-slos/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/check-interval", "name": "Check Interval", "description": "How often a monitor runs — e.g. every 30 seconds, 1 minute, or 5 minutes. Shorter intervals detect outages faster but increase load and cost.", "url": "https://foursight.cloud/glossary/check-interval", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "check-interval", "sameAs": [ "https://sre.google/sre-book/monitoring-distributed-systems/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/consecutive-failure-threshold", "name": "Consecutive Failure Threshold", "description": "The number of failed checks in a row required before an incident is opened. Higher thresholds reduce noise but slow detection.", "url": "https://foursight.cloud/glossary/consecutive-failure-threshold", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "consecutive-failure-threshold", "sameAs": [ "https://sre.google/workbook/alerting-on-slos/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/incident", "name": "Incident", "description": "An unplanned event that disrupts service or threatens to. Incidents have severity, an owner, a timeline, and end with a resolution and (for serious ones) a post-mortem.", "url": "https://foursight.cloud/glossary/incident", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "incident", "sameAs": [ "https://response.pagerduty.com/before/what_is_an_incident/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/severity", "name": "Severity (SEV-1 to SEV-4)", "description": "A standardized scale for how serious an incident is. SEV-1 is a full outage; SEV-4 is cosmetic. Severity drives response time, who's paged, and whether status-page comms are required.", "url": "https://foursight.cloud/glossary/severity", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "severity", "sameAs": [ "https://response.pagerduty.com/before/severity_levels/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/incident-commander", "name": "Incident Commander (IC)", "description": "The single person who owns coordination of an incident end-to-end. The IC doesn't write the fix — they decide severity, assign roles, drive comms, and call the all-clear.", "url": "https://foursight.cloud/glossary/incident-commander", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "incident-commander", "sameAs": [ "https://response.pagerduty.com/training/incident_commander/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/tech-lead", "name": "Tech Lead (during incident)", "description": "The engineer actively diagnosing and fixing the problem during an incident. Reports findings up to the Incident Commander.", "url": "https://foursight.cloud/glossary/tech-lead", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "tech-lead", "sameAs": [ "https://response.pagerduty.com/before/different_roles/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/comms-lead", "name": "Comms Lead", "description": "Owns customer-facing communication during an incident — status page updates, in-product banners, support team briefings. Frees engineers to focus on the technical fix.", "url": "https://foursight.cloud/glossary/comms-lead", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "comms-lead", "sameAs": [ "https://response.pagerduty.com/before/different_roles/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/on-call-rotation", "name": "On-Call Rotation", "description": "A scheduled rotation of engineers who are responsible for responding to alerts outside business hours. Sustainable rotations are weekly and shared across at least 4–5 people.", "url": "https://foursight.cloud/glossary/on-call-rotation", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "on-call-rotation", "sameAs": [ "https://sre.google/sre-book/being-on-call/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/escalation-policy", "name": "Escalation Policy", "description": "Rules that decide who gets paged next if the primary on-call doesn't acknowledge within a timeout. Typically: primary → secondary → engineering manager.", "url": "https://foursight.cloud/glossary/escalation-policy", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "escalation-policy", "sameAs": [ "https://support.pagerduty.com/main/docs/escalation-policies" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/alert-fatigue", "name": "Alert Fatigue", "description": "Desensitization caused by too many low-quality alerts. Leads to slower response times, missed real incidents, and on-call burnout.", "url": "https://foursight.cloud/glossary/alert-fatigue", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "alert-fatigue", "sameAs": [ "https://sre.google/workbook/alerting-on-slos/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/runbook", "name": "Runbook", "description": "A concise, action-oriented document telling an on-call engineer exactly what to do when a specific alert fires — diagnostic queries, remediation commands, escalation contacts.", "url": "https://foursight.cloud/glossary/runbook", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "runbook", "sameAs": [ "https://sre.google/workbook/on-call/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/playbook", "name": "Playbook", "description": "A broader process document covering how a team responds to incidents in general — severity rubric, roles, comms templates, post-mortem requirements. Distinct from a runbook, which is alert-specific.", "url": "https://foursight.cloud/glossary/playbook", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "playbook", "sameAs": [ "https://response.pagerduty.com/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/post-mortem", "name": "Post-Mortem", "description": "A written analysis published after an incident covering what happened, when, why, and what will change. Best practice is to publish public post-mortems within 5 business days of serious incidents.", "url": "https://foursight.cloud/glossary/post-mortem", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "post-mortem", "sameAs": [ "https://sre.google/sre-book/postmortem-culture/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/blameless-post-mortem", "name": "Blameless Post-Mortem", "description": "A post-mortem written in terms of \"the system allowed X\" rather than \"person Y did X.\" Removing blame is what makes engineers honest about what really happened, which is the whole point.", "url": "https://foursight.cloud/glossary/blameless-post-mortem", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "blameless-post-mortem", "sameAs": [ "https://sre.google/sre-book/postmortem-culture/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/root-cause", "name": "Root Cause", "description": "The underlying systemic reason an incident occurred — not just the trigger. Mature post-mortems usually identify multiple contributing causes rather than a single \"root.\"", "url": "https://foursight.cloud/glossary/root-cause", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "root-cause", "sameAs": [ "https://sre.google/sre-book/postmortem-culture/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/five-whys", "name": "Five Whys", "description": "A root-cause analysis technique where you ask \"why?\" five times in sequence, each answer pointing one level deeper, to reach a systemic cause rather than a symptom.", "url": "https://foursight.cloud/glossary/five-whys", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "five-whys", "sameAs": [ "https://www.lean.org/lexicon-terms/5-whys/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/blast-radius", "name": "Blast Radius", "description": "The scope of users, systems, or data affected by an incident. \"Limit the blast radius\" means contain the failure to as small a group as possible.", "url": "https://foursight.cloud/glossary/blast-radius", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "blast-radius", "sameAs": [ "https://docs.aws.amazon.com/wellarchitected/latest/reliability-pillar/welcome.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/mitigation", "name": "Mitigation vs Resolution", "description": "Mitigation stops the bleeding (rollback, failover, scale up). Resolution is the permanent fix. During an incident, mitigate first — resolution can wait until the customers are unaffected.", "url": "https://foursight.cloud/glossary/mitigation", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "mitigation", "sameAs": [ "https://sre.google/sre-book/managing-incidents/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/status-page", "name": "Status Page", "description": "A public web page showing the current operational state of your services and a history of incidents. Reduces inbound support volume during outages and signals operational maturity to prospects.", "url": "https://foursight.cloud/glossary/status-page", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "status-page", "sameAs": [ "https://www.atlassian.com/incident-management/status-page" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/status-component", "name": "Status Component", "description": "A logical group on a status page (e.g. \"API\", \"Dashboard\", \"Webhooks\") representing one customer-facing service. Components have their own status indicator that aggregates underlying monitors.", "url": "https://foursight.cloud/glossary/status-component", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "status-component", "sameAs": [ "https://support.atlassian.com/statuspage/docs/show-service-status-with-components/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/maintenance-window", "name": "Maintenance Window", "description": "A pre-announced period when a service may be unavailable for planned work. Industry norms: 48–72 hours' notice for scheduled maintenance, with start/end time and affected components.", "url": "https://foursight.cloud/glossary/maintenance-window", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "maintenance-window", "sameAs": [ "https://support.atlassian.com/statuspage/docs/schedule-maintenance/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/http-status-codes", "name": "HTTP Status Codes (2xx / 4xx / 5xx)", "description": "Three-digit response codes returned by HTTP servers. 2xx = success, 3xx = redirect, 4xx = client error (bad request), 5xx = server error. Monitoring tools alert on 4xx/5xx codes.", "url": "https://foursight.cloud/glossary/http-status-codes", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "http-status-codes", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc9110#name-status-codes", "https://developer.mozilla.org/en-US/docs/Web/HTTP/Status" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/timeout", "name": "Timeout", "description": "The maximum time a client waits for a response before giving up. Common timeout layers: DNS, TCP connect, TLS handshake, HTTP request, and application-level.", "url": "https://foursight.cloud/glossary/timeout", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "timeout", "sameAs": [ "https://developer.mozilla.org/en-US/docs/Web/HTTP/Connection_management_in_HTTP_1.x" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/dns", "name": "DNS (Domain Name System)", "description": "The internet's address book — translates human-readable domain names like foursight.cloud into IP addresses that computers route traffic to.", "url": "https://foursight.cloud/glossary/dns", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "dns", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc1035" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/a-record", "name": "A Record", "description": "A DNS record that maps a hostname to an IPv4 address (e.g. `foursight.cloud → 76.76.21.21`).", "url": "https://foursight.cloud/glossary/a-record", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "a-record", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc1035#section-3.4.1" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/aaaa-record", "name": "AAAA Record", "description": "Maps a hostname to an IPv6 address. Functionally the IPv6 equivalent of an A record.", "url": "https://foursight.cloud/glossary/aaaa-record", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "aaaa-record", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc3596" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/cname-record", "name": "CNAME Record", "description": "An alias DNS record that points one hostname to another (e.g. `www.example.com → example.com`). Commonly used for CDN and SaaS service integrations.", "url": "https://foursight.cloud/glossary/cname-record", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "cname-record", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc1035#section-3.3.1" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/mx-record", "name": "MX Record", "description": "Identifies the mail servers responsible for accepting email for a domain.", "url": "https://foursight.cloud/glossary/mx-record", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "mx-record", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc5321" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/txt-record", "name": "TXT Record", "description": "A free-form DNS record that holds arbitrary text. 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Expired DNSSEC signatures cause complete resolution failure for validating resolvers.", "url": "https://foursight.cloud/glossary/dnssec", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "dnssec", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc4033" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/cdn", "name": "CDN (Content Delivery Network)", "description": "A globally distributed network of cache servers that serve content from the location closest to each user, reducing latency and origin load.", "url": "https://foursight.cloud/glossary/cdn", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "cdn", "sameAs": [ "https://developer.mozilla.org/en-US/docs/Glossary/CDN" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/edge-pop", "name": "Edge / Edge POP", "description": "A CDN's \"point of presence\" — a physical location near end users that caches and serves content. \"Edge functions\" run small bits of compute at these locations.", "url": "https://foursight.cloud/glossary/edge-pop", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "edge-pop", "sameAs": [ "https://www.cloudflare.com/learning/cdn/glossary/edge-server/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/isr", "name": "ISR (Incremental Static Regeneration)", "description": "A Next.js feature that lets statically generated pages refresh in the background on a schedule or on-demand, without rebuilding the whole site.", "url": "https://foursight.cloud/glossary/isr", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "isr", "sameAs": [ "https://vercel.com/docs/incremental-static-regeneration" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/cold-start", "name": "Cold Start", "description": "The latency penalty incurred the first time a serverless function runs after a period of inactivity, while the runtime is being initialized. Can range from tens of milliseconds to several seconds.", "url": "https://foursight.cloud/glossary/cold-start", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "cold-start", "sameAs": [ "https://docs.aws.amazon.com/lambda/latest/operatorguide/execution-environments.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/throttling", "name": "Throttling", "description": "Deliberately slowing or rejecting requests once a defined rate has been exceeded, to protect a service from overload.", "url": "https://foursight.cloud/glossary/throttling", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "throttling", "sameAs": [ "https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-request-throttling.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/rate-limit", "name": "Rate Limit", "description": "A cap on how many requests a client may make to an API in a given time window. Exceeding the limit typically returns HTTP 429 Too Many Requests.", "url": "https://foursight.cloud/glossary/rate-limit", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "rate-limit", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc6585#section-4" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/ssl-tls", "name": "SSL / TLS", "description": "Transport Layer Security (TLS) is the cryptographic protocol that powers HTTPS. \"SSL\" is the deprecated predecessor — when people say \"SSL\" today they almost always mean TLS.", "url": "https://foursight.cloud/glossary/ssl-tls", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "ssl-tls", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc8446" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/tls-13", "name": "TLS 1.2 vs TLS 1.3", "description": "TLS 1.3 (2018) is faster (one round-trip handshake) and more secure (removed legacy ciphers) than TLS 1.2. TLS 1.0 and 1.1 are deprecated and should not be supported.", "url": "https://foursight.cloud/glossary/tls-13", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "tls-13", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc8446", "https://datatracker.ietf.org/doc/html/rfc8996" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/certificate", "name": "TLS Certificate (Leaf, Intermediate, Root CA)", "description": "An X.509 certificate is a signed document binding a public key to a domain. The leaf is your server's cert; intermediates are signed by a trusted root Certificate Authority (CA) that browsers already trust.", "url": "https://foursight.cloud/glossary/certificate", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "certificate", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc5280" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/certificate-chain", "name": "Certificate Chain", "description": "The sequence of certificates linking your server's leaf cert back to a trusted root CA. An incomplete chain is the most common SSL gotcha — works in Chrome (which caches intermediates) but fails on iOS Safari, Android, and many HTTP clients.", "url": "https://foursight.cloud/glossary/certificate-chain", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "certificate-chain", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc5280#section-6" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/wildcard-certificate", "name": "Wildcard Certificate", "description": "A TLS cert valid for one subdomain level — `*.example.com` covers `api.example.com` but NOT `v2.api.example.com`.", "url": "https://foursight.cloud/glossary/wildcard-certificate", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "wildcard-certificate", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc6125#section-6.4.3" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/lets-encrypt", "name": "Let's Encrypt", "description": "A free, automated, non-profit Certificate Authority issuing 90-day TLS certificates. Industry standard for auto-renewed certs on most modern web infrastructure.", "url": "https://foursight.cloud/glossary/lets-encrypt", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "lets-encrypt", "sameAs": [ "https://letsencrypt.org/how-it-works/", "https://datatracker.ietf.org/doc/html/rfc8555" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/hsts", "name": "HSTS (HTTP Strict Transport Security)", "description": "An HTTP response header that tells browsers to only ever connect to your site over HTTPS — protects against SSL-stripping attacks. Best practice: `max-age=31536000; includeSubDomains; preload`.", "url": "https://foursight.cloud/glossary/hsts", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "hsts", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc6797" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/ocsp-stapling", "name": "OCSP Stapling", "description": "An optimization where your server periodically fetches a signed certificate-validity statement from the CA and \"staples\" it to the TLS handshake — avoiding a separate revocation check from the user's browser.", "url": "https://foursight.cloud/glossary/ocsp-stapling", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "ocsp-stapling", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc6066#section-8" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/cipher-suite", "name": "Cipher Suite", "description": "The bundle of cryptographic algorithms a TLS connection uses (key exchange + bulk cipher + MAC). 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AES-GCM and ChaCha20-Poly1305 are the standard AEAD ciphers in TLS 1.2 and the only ones allowed in TLS 1.3.", "url": "https://foursight.cloud/glossary/aead", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "aead", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc5116" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/ecdhe", "name": "ECDHE (Elliptic Curve Diffie-Hellman Ephemeral)", "description": "A key-exchange algorithm that gives every TLS session a fresh, ephemeral key — providing forward secrecy so past traffic stays safe even if a server's long-term key is later compromised.", "url": "https://foursight.cloud/glossary/ecdhe", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "ecdhe", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.7" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/cert-pinning", "name": "Certificate Pinning", "description": "A mobile-app technique where the client only accepts a specific server certificate (or its issuing CA), even if other certs would otherwise be trusted. Stops MITM attacks but breaks completely if you rotate certs without updating the app.", "url": "https://foursight.cloud/glossary/cert-pinning", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "cert-pinning", "sameAs": [ "https://owasp.org/www-community/controls/Certificate_and_Public_Key_Pinning" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/signature-verification", "name": "Signature Verification", "description": "The process of checking that a message hasn't been tampered with by re-computing a cryptographic signature with a shared secret or public key and comparing. Used in webhook payloads, JWTs, and TLS handshakes.", "url": "https://foursight.cloud/glossary/signature-verification", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "signature-verification", "sameAs": [ "https://csrc.nist.gov/publications/detail/fips/198/1/final" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/hmac", "name": "HMAC (Hash-based Message Authentication Code)", "description": "A construction for verifying message integrity and authenticity using a shared secret and a hash function (e.g. HMAC-SHA256). Stripe, GitHub, and most webhook providers sign payloads with HMAC.", "url": "https://foursight.cloud/glossary/hmac", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "hmac", "sameAs": [ "https://datatracker.ietf.org/doc/html/rfc2104", "https://csrc.nist.gov/publications/detail/fips/198/1/final" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/webhook-secret", "name": "Webhook Secret", "description": "A shared secret used to sign webhook payloads with HMAC so the receiver can verify they came from the legitimate sender and weren't modified in transit.", "url": "https://foursight.cloud/glossary/webhook-secret", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "webhook-secret", "sameAs": [ "https://docs.stripe.com/webhooks#verify-events" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/mrr", "name": "MRR (Monthly Recurring Revenue)", "description": "The predictable monthly subscription revenue a SaaS earns, normalized so annual plans count as 1/12 per month.", "url": "https://foursight.cloud/glossary/mrr", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "mrr", "sameAs": [ "https://stripe.com/resources/more/what-is-monthly-recurring-revenue" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/arr", "name": "ARR (Annual Recurring Revenue)", "description": "Annualised subscription revenue, i.e. MRR × 12. Standard top-line metric for SaaS valuation and growth tracking.", "url": "https://foursight.cloud/glossary/arr", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "arr", "sameAs": [ "https://stripe.com/resources/more/what-is-annual-recurring-revenue-a-guide-for-saas-businesses" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/acv", "name": "ACV (Annual Contract Value)", "description": "The yearly value of a single customer contract, normalized to one year. Used to size and segment enterprise sales pipelines.", "url": "https://foursight.cloud/glossary/acv", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "acv", "sameAs": [ "https://blog.hubspot.com/sales/annual-contract-value-acv" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/churn", "name": "Churn", "description": "The rate at which customers cancel or downgrade. 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Used for custom server logic, webhooks, and integrations with third-party APIs.", "url": "https://foursight.cloud/glossary/supabase-edge-functions", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "supabase-edge-functions", "sameAs": [ "https://supabase.com/docs/guides/functions" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/postgres-connection-pool", "name": "Postgres Connection Pool", "description": "A managed set of pre-opened Postgres connections shared across application requests. Without pooling, every request opens a fresh connection and the database quickly saturates.", "url": "https://foursight.cloud/glossary/postgres-connection-pool", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "postgres-connection-pool", "sameAs": [ "https://www.postgresql.org/docs/current/runtime-config-connection.html", "https://supabase.com/docs/guides/database/connecting-to-postgres" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/aws-lambda", "name": "AWS Lambda", "description": "Amazon's serverless function-as-a-service product — runs your code in response to events without you managing servers. Has measurable cold-start latency the first time a function runs after idle.", "url": "https://foursight.cloud/glossary/aws-lambda", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "aws-lambda", "sameAs": [ "https://docs.aws.amazon.com/lambda/latest/dg/welcome.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/api-gateway", "name": "API Gateway", "description": "A managed service (most commonly AWS API Gateway) that fronts your backend with routing, rate-limiting, auth, throttling, and request transformation.", "url": "https://foursight.cloud/glossary/api-gateway", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "api-gateway", "sameAs": [ "https://docs.aws.amazon.com/apigateway/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/cloudflare-workers", "name": "Cloudflare Workers", "description": "Cloudflare's edge serverless runtime — JavaScript or WebAssembly running in V8 isolates across hundreds of edge locations with sub-millisecond cold starts.", "url": "https://foursight.cloud/glossary/cloudflare-workers", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "cloudflare-workers", "sameAs": [ "https://developers.cloudflare.com/workers/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/kv-store", "name": "KV Store", "description": "A globally distributed key-value store (Cloudflare Workers KV, Vercel KV, etc.). Eventually consistent — writes can take up to ~60 seconds to propagate across all edge locations.", "url": "https://foursight.cloud/glossary/kv-store", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "kv-store", "sameAs": [ "https://developers.cloudflare.com/kv/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/blue-green-deploy", "name": "Blue-Green Deployment", "description": "A zero-downtime release strategy with two identical environments. New version deploys to the idle (\"green\") environment; traffic cuts over instantly once it's verified healthy. Instant rollback by switching back.", "url": "https://foursight.cloud/glossary/blue-green-deploy", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "blue-green-deploy", "sameAs": [ "https://martinfowler.com/bliki/BlueGreenDeployment.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/rolling-deploy", "name": "Rolling Deployment", "description": "A release strategy that replaces instances of an old version with the new version gradually, a few at a time, keeping the service available throughout.", "url": "https://foursight.cloud/glossary/rolling-deploy", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "rolling-deploy", "sameAs": [ "https://docs.aws.amazon.com/AmazonECS/latest/developerguide/deployment-types.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/failover", "name": "Failover", "description": "Switching automatically (or manually) from a failed primary system to a healthy standby. Common patterns: DNS failover, database failover replicas, multi-region active-passive.", "url": "https://foursight.cloud/glossary/failover", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "failover", "sameAs": [ "https://docs.aws.amazon.com/wellarchitected/latest/reliability-pillar/welcome.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/circuit-breaker", "name": "Circuit Breaker", "description": "A pattern where a client temporarily stops calling a failing downstream service after a threshold of errors, returns fast failures, and periodically tests if the service has recovered.", "url": "https://foursight.cloud/glossary/circuit-breaker", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "circuit-breaker", "sameAs": [ "https://martinfowler.com/bliki/CircuitBreaker.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/queue-saturation", "name": "Queue Saturation", "description": "A failure mode where work arrives at a queue faster than it's processed, the queue grows unbounded, and latency cascades. Often happens during traffic spikes or after a worker outage.", "url": "https://foursight.cloud/glossary/queue-saturation", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "queue-saturation", "sameAs": [ "https://sre.google/sre-book/handling-overload/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/etl-pipeline", "name": "ETL Pipeline", "description": "\"Extract, Transform, Load\" — a scheduled data pipeline that pulls data from a source, transforms it, and writes it to a destination (data warehouse, analytics DB). Silent ETL failures often go undetected for days without heartbeat monitoring.", "url": "https://foursight.cloud/glossary/etl-pipeline", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "etl-pipeline", "sameAs": [ "https://aws.amazon.com/what-is/etl/" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/cron-job", "name": "Cron Job", "description": "A scheduled task that runs at fixed times or intervals, defined by a `crontab` expression. Originally a Unix utility; the name is now used for any scheduled background job.", "url": "https://foursight.cloud/glossary/cron-job", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "cron-job", "sameAs": [ "https://pubs.opengroup.org/onlinepubs/9699919799/utilities/crontab.html" ] }, { "@type": "DefinedTerm", "@id": "https://foursight.cloud/glossary/tabletop-exercise", "name": "Tabletop Exercise", "description": "A simulated incident walked through verbally by the team — no actual production impact — to test the playbook, rehearse roles, and uncover gaps before a real incident.", "url": "https://foursight.cloud/glossary/tabletop-exercise", "inDefinedTermSet": "https://foursight.cloud/glossary", "termCode": "tabletop-exercise", "sameAs": [ "https://www.cisa.gov/resources-tools/services/cisa-tabletop-exercise-packages" ] } ] } --- [FourSight ](/) [Features](/#features)[Pricing](/pricing)[Guides](/guides)[Glossary](/glossary)[FAQ](/faq) [Login](/auth)[Start free](/auth?signup=true) [Start free](/auth?signup=true) # Monitoring & Reliability Glossary Plain-English definitions for the technical terms used across our guides — each cited from primary, authoritative sources (IETF, NIST, Google SRE, MDN, Stripe, AWS). AllMonitoring & UptimeIncidents & On-CallWeb & NetworkingSecurity & TLSSaaS & BillingPlatformsOperations ABCDEFGHIJ KLMN OPQRSTUV WX Y Z ## A 9 terms · 109 total ### [A Record](/glossary/a-record) Web & Networking A DNS record that maps a hostname to an IPv4 address (e.g. \`foursight.cloud → 76.76.21.21\`). Primary source - IETF — [RFC 1035 §3.4.1 — A RDATA format](https://datatracker.ietf.org/doc/html/rfc1035#section-3.4.1) ### [AAAA Record](/glossary/aaaa-record) Web & Networking Maps a hostname to an IPv6 address. Functionally the IPv6 equivalent of an A record. Primary source - IETF — [RFC 3596 — DNS Extensions to Support IP Version 6](https://datatracker.ietf.org/doc/html/rfc3596) ### [ACV (Annual Contract Value)](/glossary/acv) SaaS & Billing The yearly value of a single customer contract, normalized to one year. Used to size and segment enterprise sales pipelines. Primary source - HubSpot — [ACV explained](https://blog.hubspot.com/sales/annual-contract-value-acv) ### [AEAD (Authenticated Encryption with Associated Data)](/glossary/aead) Security & TLS A class of ciphers that encrypt data and authenticate it in a single operation. AES-GCM and ChaCha20-Poly1305 are the standard AEAD ciphers in TLS 1.2 and the only ones allowed in TLS 1.3. Primary source - IETF — [RFC 5116 — AEAD Interface](https://datatracker.ietf.org/doc/html/rfc5116) ### [Alert Fatigue](/glossary/alert-fatigue) Incidents & On-Call Desensitization caused by too many low-quality alerts. Leads to slower response times, missed real incidents, and on-call burnout. Primary source - Google SRE Workbook — [Alerting on SLOs](https://sre.google/workbook/alerting-on-slos/) [Related guide: Alerting Without Alert Fatigue](/guides/alerting-without-alert-fatigue) ### [API Gateway](/glossary/api-gateway) Platforms A managed service (most commonly AWS API Gateway) that fronts your backend with routing, rate-limiting, auth, throttling, and request transformation. Primary source - AWS Docs — [Amazon API Gateway](https://docs.aws.amazon.com/apigateway/) ### [ARR (Annual Recurring Revenue)](/glossary/arr) SaaS & Billing Annualised subscription revenue, i.e. MRR × 12. Standard top-line metric for SaaS valuation and growth tracking. Primary source - Stripe — [Annual recurring revenue](https://stripe.com/resources/more/what-is-annual-recurring-revenue-a-guide-for-saas-businesses) ### [Availability vs Reliability](/glossary/availability-vs-reliability) Monitoring & Uptime Availability measures whether a service responds (uptime %). Reliability measures whether it responds correctly and within acceptable latency. A service can be available but unreliable if responses are slow or wrong. Primary source - Google SRE Book — [Chapter 3: Embracing Risk](https://sre.google/sre-book/embracing-risk/) ### [AWS Lambda](/glossary/aws-lambda) Platforms Amazon's serverless function-as-a-service product — runs your code in response to events without you managing servers. Has measurable cold-start latency the first time a function runs after idle. Primary source - AWS Docs — [AWS Lambda Developer Guide](https://docs.aws.amazon.com/lambda/latest/dg/welcome.html) [Related guide: Monitoring AWS Lambda & API Gateway](/guides/monitoring-aws-lambda-apis) #### Explore [All guides →](/guides)[Pricing →](/pricing)[FAQ →](/faq) 10 free commercial-safe monitors [Start free](/auth?signup=true) FourSight © 2026 [TetraCore](https://tetracorehq.com/). All rights reserved. FourSight is a TetraCore product — Bowling Green, Ohio. 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