Monitoring & DevOps Glossary

Clear definitions for the terms that matter most in uptime monitoring, incident management, and site reliability engineering.

A B C D E F H I L M O P R S T U W

A

Alert Fatigue

A condition where responders become desensitized to alerts due to excessive volume or frequent false positives.

Availability

The proportion of time a system is functional and accessible, often expressed as a percentage.

Auto-Scaling

The automatic adjustment of compute resources based on current demand to maintain performance and control costs.

Apdex Score

A standardized metric that rates user satisfaction with application response time on a scale from 0 to 1.

API Monitoring

The practice of monitoring API endpoints for availability, performance, correctness, and compliance with expected behavior.

Alert Routing

The process of directing alerts to the appropriate team or individual based on rules, service ownership, and severity.

Agent-Based Monitoring

Monitoring that runs a small collector process on the machine itself so it can report metrics no external probe can reach.

B

Blue-Green Deployment

A deployment strategy using two identical production environments, where traffic is switched from the current (blue) to the new (green) version.

Black-Box Monitoring

Monitoring a system from the outside, testing externally visible behavior without knowledge of internal implementation.

Blameless Postmortem

An incident review process that focuses on systemic improvements rather than individual fault.

C

Cron Job

A scheduled task that runs automatically at specified intervals, defined using a cron expression.

Canary Deployment

A deployment strategy that rolls out changes to a small subset of users before a full release to detect issues early.

CPU Utilization

The share of wall clock time a CPU spends executing work instead of idling, broken down by states such as user, system, and iowait.

D

Downtime

A period when a system or service is unavailable or not functioning correctly for its users.

DORA Metrics

Four key metrics identified by the DORA team for measuring software delivery performance: deployment frequency, lead time, change failure rate, and MTTR.

DNS Monitoring

Monitoring that checks DNS resolution to ensure domain names resolve correctly and within acceptable time.

Disk I/O

The traffic between an operating system and its block devices, counted as bytes read and written per device over time.

E

Escalation Policy

A set of rules defining how alerts are routed and escalated when the primary responder does not acknowledge them in time.

Error Budget

The maximum amount of unreliability a service can have within a given period, derived from the SLO.

F

Five Nines (99.999% Uptime)

A reliability standard allowing no more than 5 minutes and 15 seconds of downtime per year.

Filesystem Usage

How much space is used and free on each mounted filesystem, expressed in bytes and as a percentage of capacity.

H

Health Check

An endpoint or process that verifies whether a service or its dependencies are functioning correctly.

HTTP Status Code

A three-digit code returned by a web server indicating the result of the client's request.

Host Metrics

Resource measurements a machine reports about itself, covering CPU, memory, filesystem, disk I/O, and network interfaces.

I

Incident Severity

A classification system that categorizes incidents by their impact and urgency to prioritize response efforts.

I/O Wait (iowait)

The share of CPU time during which a processor sat idle with at least one of its own I/O requests still outstanding.

L

Latency

The time delay between a request being sent and the response being received, typically measured in milliseconds.

Load Average

A rolling count of how many tasks are competing for the CPU, reported by the kernel over the last 1, 5, and 15 minutes.

M

MTTR (Mean Time to Recover)

The average time it takes to restore a system or service after a failure or incident, and the anchor metric of the four mean-time measures (MTTD, MTTA, MTBF, MTTF).

Maintenance Window

A scheduled period during which a system is intentionally taken offline or degraded for updates, patches, or infrastructure changes.

Memory Utilization

The share of a host RAM in use, best judged by how much memory remains available to new processes rather than how much is nominally used.

O

On-Call

A rotation system where team members are designated to respond to alerts and incidents outside normal working hours.

On-Call Rotation

A schedule that determines which team member is the primary responder for alerts during each time period.

OpenTelemetry

A vendor neutral CNCF project that standardizes how telemetry is generated and exported, covering both the data model and the OTLP protocol.

P

Post-Mortem (Incident Review)

A structured review conducted after an incident to identify root causes and prevent recurrence.

P99 Latency

The response time below which 99% of requests are served — used to measure tail latency and worst-case user experience.

R

RTO (Recovery Time Objective)

The maximum acceptable duration of time a service can be offline after a disaster or failure before causing unacceptable business impact.

RPO (Recovery Point Objective)

The maximum acceptable amount of data loss measured in time — how far back in time your recovery point can be.

Response Time

The total time elapsed between sending a request and receiving the complete response from a server.

S

SLA (Service Level Agreement)

A formal contract defining the expected level of service, including uptime guarantees, between a provider and customer.

SLO (Service Level Objective)

An internal target for service reliability, typically more ambitious than the external SLA.

Status Page

A public-facing page that communicates the current operational status of a service to users and stakeholders.

Synthetic Monitoring

Proactive monitoring that simulates user interactions to test service availability and performance from external locations.

SSL Certificate

A digital certificate that authenticates a website's identity and enables encrypted HTTPS connections.

SRE (Site Reliability Engineering)

A discipline that applies software engineering practices to infrastructure and operations to build scalable and reliable systems.

Server Monitoring

Collecting and alerting on the resource health of individual machines: CPU, memory, filesystem, disk I/O, and network.

T

Throughput

The rate at which a system processes requests or data, typically measured in requests per second.

TCP Monitoring

Monitoring that checks the availability and response time of services by establishing TCP connections to specific ports.

TLS Handshake

The initial negotiation process between a client and server that establishes an encrypted HTTPS connection.

U

Uptime

The percentage of time a system or service is operational and accessible to users.

Uptime SLA

The specific uptime percentage guaranteed in a service level agreement, defining maximum allowable downtime.

W

Webhook

An HTTP callback that sends real-time data to a specified URL when a specific event occurs.

White-Box Monitoring

Monitoring based on internal system metrics, logs, and traces that reveal the internal state and behavior of a service.

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