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DevOps Glossary
59+ DevOps and cloud infrastructure terms explained in plain language.
- Ansible
- An open-source automation tool for configuration management, application deployment, and task automation. Ansible uses YAML-based playbooks and operates agentlessly over SSH, making it simple to get started without installing software on target machines.
- Linux Commands for DevOps
- API Gateway
- A server that acts as the single entry point for a set of microservices. It handles request routing, composition, rate limiting, and authentication so that individual services don't need to implement these concerns themselves.
- Nginx Reverse Proxy Guide
- ArgoCD
- A declarative GitOps continuous delivery tool for Kubernetes. ArgoCD continuously compares the live state in the cluster with the desired state in Git, reports any drift as OutOfSync, and syncs the two either on demand or automatically when an automated sync policy is enabled, keeping an audit trail of application events.
- GitOps & KubernetesKubernetes 101
- Auto Scaling
- The ability to automatically adjust the number of running compute resources based on real-time demand. Auto scaling ensures applications can handle traffic spikes without over-provisioning during quiet periods, optimizing both performance and cost.
- requests vs limitsResource calculator
- Blue-Green Deployment
- A release strategy that runs two identical production environments called 'blue' and 'green.' Traffic is switched from one to the other once the new version is verified, enabling instant rollback by redirecting traffic back to the previous environment.
- A deploy reports success but users see errorsWhy artifacts should be immutable
- Canary Release
- A deployment technique where a new version is rolled out to a small subset of users before being promoted to the entire fleet. This limits the blast radius of bugs and allows teams to monitor real-world performance before full rollout.
- A deploy reports success but users see errorsReadiness vs liveness
- CI/CD
- Continuous Integration and Continuous Delivery/Deployment — the practice of automating the build, test, and release process. CI merges code changes frequently and runs automated tests. Continuous delivery keeps every change that passes in a releasable state, so it can go to production at any time; continuous deployment goes one step further and releases every passing change to production automatically.
- CI/CD security riskssts:AssumeRoleWithWebIdentity refusedCI/CD with GitHub Actions
- ConfigMap
- A Kubernetes object used to store non-confidential configuration data as key-value pairs. ConfigMaps decouple configuration from container images, allowing the same image to be used across different environments with different settings.
- Kubernetes 101
- Container
- A running instance of an image: an isolated process with its own view of the filesystem, network and other system resources, plus a thin writable layer on top of the image's read-only layers that is discarded when the container is deleted. Containers share the host OS kernel, making them far more efficient than traditional virtual machines.
- Why containers are not virtual machinesImage vs containerDocker Guide
- Container Registry
- A service for storing and distributing container images. A registry holds many repositories, each a collection of related images. Registries like Docker Hub, GitHub Container Registry, and Amazon ECR allow teams to push, pull, and version their images as part of the CI/CD pipeline.
- ImagePullBackOffDocker Guide
- DaemonSet
- A Kubernetes controller that ensures a copy of a specific Pod runs on every (or selected) node in the cluster. DaemonSets are commonly used for node-level concerns like log collection agents, monitoring exporters, and network proxies.
- Kubernetes 101
- Deployment
- A Kubernetes resource that manages a set of identical Pods and provides declarative updates, rolling updates, and rollback to an earlier revision on request; it does not roll back a failed rollout by itself. Deployments are the standard way to run stateless applications on Kubernetes.
- Why Kubernetes uses desired stateKubernetes 101
- DevOps
- A way of building and running software in which the people who write it and the people who operate it share responsibility for how it behaves in production, and automate the path between the two. In practice that means small changes merged often (continuous integration), an automated route to production (continuous delivery), infrastructure described in code, and monitoring that tells the team quickly when something breaks. It is a set of practices and a way of working rather than a single tool. DORA's research measures it with four numbers: how often a team deploys, how long a change takes to reach production, how often a deployment fails, and how quickly the team recovers when one does.
- CI/CD with GitHub ActionsCI/CD security risksError budget calculator
- Docker
- A platform for building, shipping, and running applications inside containers. Docker uses OS-level virtualization to deliver software in portable, reproducible packages that work identically across development, staging, and production.
- Container exits immediatelyDocker Guide
- Docker Compose
- A tool for defining and running multi-container Docker applications using a YAML configuration file. With a single command you can spin up all the services your app needs — databases, caches, workers — in an isolated environment.
- Port is already allocatedDocker Compose GuideDocker Guide
- Docker Swarm
- Docker Engine's built-in orchestration mode (swarm mode), which joins Docker hosts into a cluster of managers and workers and keeps each service at the number of replicas you declare. Swarm provides service discovery, load balancing, and rolling updates with a simpler learning curve than Kubernetes.
- Docker Swarm Guide
- ECS
- Amazon Elastic Container Service — a fully managed container orchestration service from AWS. AWS runs the orchestration control plane for you; the containers run on capacity you choose — AWS Fargate or ECS Managed Instances, where AWS manages the servers, or EC2 instances you manage yourself. ECS integrates tightly with other AWS services like ALB and CloudWatch.
- Docker Guide
- EKS
- Amazon Elastic Kubernetes Service — a managed Kubernetes service that runs the Kubernetes control plane across multiple AWS availability zones. EKS removes the operational burden of running your own Kubernetes control plane, and with EKS Auto Mode it can manage the worker nodes too.
- Kubernetes 101
- Envoy
- A high-performance, open-source edge and service proxy designed for cloud-native applications. Envoy handles load balancing, observability, and TLS termination, and is the data plane behind popular service meshes like Istio.
- Firewall
- A network security system that monitors and controls incoming and outgoing traffic based on predetermined rules. In cloud environments, firewalls are often implemented as security groups or network ACLs that restrict access to specific ports and IP ranges.
- Security group vs network ACLCIDR calculator
- Git
- A distributed version control system that tracks changes in source code during development. Git enables branching, merging, and collaboration, and is the foundation of modern DevOps workflows including GitOps and CI/CD pipelines.
- GitOps & Kubernetes
- GitOps
- An operational framework where the desired state of applications and infrastructure is declared in a versioned store, usually Git, which serves as the single source of truth. Changes are made by committing to it (typically through pull requests), and software agents automatically pull that state and continuously reconcile the running system toward it.
- Why Kubernetes uses desired stateGitOps & Kubernetes
- Grafana
- An open-source analytics and visualization platform commonly used for monitoring dashboards. Grafana connects to data sources like Prometheus, Loki, and Elasticsearch, allowing teams to create rich, interactive dashboards for metrics and logs.
- Monitoring with Prometheus & Grafana
- Health Check
- An endpoint or mechanism that reports whether a service is running correctly. Health checks are used by load balancers, orchestrators, and monitoring systems to detect failures and automatically route traffic away from unhealthy instances.
- Readiness vs liveness
- Helm
- A package manager for Kubernetes whose packages, called 'charts', are collections of files — chiefly templated Kubernetes manifests and their default values — used to define, install, and upgrade applications. Helm simplifies complex deployments by bundling related Kubernetes resources into a single, versioned package.
- requests vs limitsKubernetes 101GitOps & Kubernetes
- HPA
- Horizontal Pod Autoscaler — a Kubernetes resource that automatically scales the number of Pod replicas based on observed CPU utilization, memory usage, or custom metrics. HPA enables applications to handle variable workloads without manual intervention.
- requests vs limitsKubernetes 101
- Idempotent
- A property of an operation meaning that executing it multiple times has the same effect as executing it once. Idempotency is critical in DevOps for configuration management, API design, and deployment scripts where retries must be safe.
- Terraform IaC
- Image
- A read-only template used to create containers. A container image packages application code, runtime, libraries, and dependencies into a single artifact that can be versioned, shared via registries, and run identically on any compatible host.
- Image vs containerDockerfile analyzerDocker Guide
- Immutable Infrastructure
- An approach where servers or containers are never modified after deployment. Instead of patching running systems, you build a new image with the changes and replace the old instances entirely, eliminating configuration drift and improving reliability.
- Why artifacts should be immutableTerraform IaC
- Infrastructure as Code
- The practice of managing and provisioning infrastructure through machine-readable configuration files rather than manual processes. IaC tools like Terraform and Ansible make infrastructure reproducible, version-controlled, and auditable.
- Why Terraform needs stateState driftTerraform IaC
- Ingress
- A Kubernetes resource that manages external HTTP and HTTPS access to services within a cluster. An Ingress does nothing until an Ingress controller is installed; the controller handles TLS termination, name-based virtual hosting, and path-based routing. The Ingress API is stable but frozen — it is no longer being developed, though there are no plans to remove it — and Kubernetes recommends Gateway API for new work.
- 502 Bad GatewayKubernetes 101Nginx Reverse Proxy Guide
- Jenkins
- An open-source automation server widely used for building CI/CD pipelines. Jenkins supports hundreds of plugins for integration with virtually every tool in the DevOps ecosystem, though it requires more operational overhead than newer alternatives.
- CI/CD with GitHub Actions
- Kubernetes
- An open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications across clusters of machines. It works declaratively: you describe the state you want, and its controllers continuously work to move the cluster toward it.
- CrashLoopBackOffManifest analyzerKubernetes 101GitOps & Kubernetes
- Liveness Probe
- A Kubernetes health check that determines when a container needs restarting — for example, when its process is still running but deadlocked and unable to make progress. If the probe fails failureThreshold times in a row (3 by default), the kubelet kills the container and restarts it according to the pod's restart policy. A carelessly designed liveness probe can cause restarts of its own.
- Readiness vs livenessKubernetes 101
- Load Balancer
- A device or software component that distributes incoming network traffic across multiple servers to ensure no single server becomes overwhelmed. Load balancers improve availability, reliability, and responsiveness of applications.
- HTTP status explainer502 vs 504Nginx Reverse Proxy Guide
- Logging
- The practice of recording events, errors, and informational messages from applications and infrastructure. Centralized logging with tools like the ELK stack or Loki is essential for debugging, auditing, and understanding system behavior in production.
- Symptom vs cause alertingMonitoring with Prometheus & Grafana
- Microservices
- An architectural pattern where an application is composed of small, independently deployable services, each responsible for a single business capability. Microservices enable teams to develop, deploy, and scale services independently.
- Namespace
- A mechanism in Kubernetes for isolating groups of resources within a single cluster. Namespaces allow multiple teams or environments to coexist on the same cluster while providing logical boundaries for access control and resource quotas.
- ImagePullBackOffKubernetes 101
- Nginx
- A high-performance web server, reverse proxy, and load balancer. Nginx is widely used in DevOps for serving static content, terminating TLS, proxying requests to application servers, and acting as an Ingress controller in Kubernetes (through F5's NGINX Ingress Controller; the community Ingress NGINX project was retired in March 2026).
- 502 Bad Gateway504 Gateway TimeoutNginx Reverse Proxy Guide
- Node
- A physical or virtual machine in a Kubernetes cluster that runs workloads. Each node runs the kubelet agent and a container runtime, and usually kube-proxy (optional when the network plugin implements Services itself). Nodes are managed by the control plane and can be added or removed to scale the cluster.
- A node suddenly disappearsKubernetes 101
- Observability
- The ability to understand a system's internal state through its external outputs — metrics, logs, and traces. Observability goes beyond traditional monitoring by enabling engineers to ask arbitrary questions about system behavior without deploying new instrumentation.
- Symptom vs cause alertingMonitoring with Prometheus & Grafana
- Orchestration
- The automated coordination and management of multiple containers, services, or infrastructure components. Container orchestrators like Kubernetes handle scheduling, scaling, networking, and self-healing across clusters of machines.
- Kubernetes 101
- PersistentVolume
- A Kubernetes storage abstraction that provides durable storage independent of any individual Pod's lifecycle. PersistentVolumes are provisioned by administrators or dynamically by StorageClasses, and claimed by Pods through PersistentVolumeClaims.
- Kubernetes 101
- Pipeline
- An automated sequence of stages that code passes through from commit to production. A typical pipeline includes building, testing, security scanning, staging deployment, and production release, with gates between each stage.
- CI/CD security risksCI/CD with GitHub Actions
- Pod
- The smallest deployable unit in Kubernetes, consisting of one or more containers that share networking and storage. Pods are ephemeral by design — they can be created, destroyed, and replaced at any time by higher-level controllers like Deployments.
- Why pods are ephemeralPod stuck in PendingKubernetes 101
- Prometheus
- An open-source monitoring and alerting toolkit that collects and stores time-series metrics data. Prometheus uses a pull model to scrape metrics from instrumented targets and provides a powerful query language (PromQL) for analysis and alerting.
- Symptom vs cause alertingError budget calculatorMonitoring with Prometheus & Grafana
- Readiness Probe
- A Kubernetes health check that determines whether a container is ready to accept traffic. Unlike liveness probes, a failing readiness probe doesn't restart the container — it simply removes the Pod from the Service's endpoint list until it recovers.
- Readiness vs livenessKubernetes 101
- Replica Set
- A Kubernetes controller that ensures a specified number of identical Pod replicas are running at all times. While ReplicaSets are rarely created directly (Deployments manage them), they are the underlying mechanism for horizontal scaling.
- Kubernetes 101
- Rolling Update
- A deployment strategy that incrementally replaces instances of the old version with the new version in batches (a Kubernetes Deployment by default allows 25% extra and 25% unavailable Pods at a time). Rolling updates avoid downtime by keeping a minimum number of healthy instances available throughout, provided new instances only receive traffic once ready and old ones shut down gracefully.
- Why Kubernetes uses desired state
- Secret
- A Kubernetes object for storing sensitive data such as passwords, tokens, and TLS certificates. Values in a Secret's data field are base64-encoded, which is an encoding, not encryption: by default Secrets are stored unencrypted in etcd, so encryption at rest and RBAC need to be configured. Secrets can be mounted as files or injected as environment variables, keeping sensitive values out of container images.
- Why secrets do not belong in GitPush declined: secret detectedKubernetes 101
- Service
- A Kubernetes abstraction that provides stable networking for a set of Pods. Services assign a fixed IP address and DNS name to a logical group of Pods, enabling reliable communication even as individual Pods are created and destroyed.
- DNS stops resolvingKubernetes 101
- Service Mesh
- A dedicated infrastructure layer for managing service-to-service communication within a microservices architecture. Service meshes like Istio and Linkerd provide traffic management, mutual TLS, observability, and resilience features without changing application code.
- A mesh injects containers your manifest does not mentionKubernetes networking: Services, Ingress and DNS
- SLA/SLO/SLI
- Service Level Agreement, Objective, and Indicator — a hierarchy of reliability metrics. SLIs measure specific aspects of service performance, SLOs set target values for those indicators, and SLAs are contractual commitments with consequences for violations.
- SLO vs SLAError budget calculatorMonitoring with Prometheus & Grafana
- SSH
- Secure Shell — a cryptographic network protocol for operating network services securely over an unsecured network. SSH is the standard method for remotely accessing Linux servers, transferring files, and tunneling other protocols.
- Linux Commands for DevOps
- StatefulSet
- A Kubernetes controller for managing stateful applications that require stable network identities, ordered deployment, and persistent storage. StatefulSets are used for databases, message queues, and other workloads where identity and data persistence matter.
- Kubernetes 101
- Terraform
- An Infrastructure as Code tool by HashiCorp that lets you define and provision cloud and on-premises infrastructure using declarative configuration files (HCL). Since version 1.6 it has been source-available under the Business Source License rather than open source; OpenTofu is the open-source fork. Terraform manages the full lifecycle of resources through providers, plugins for cloud platforms and other APIs that number in the thousands.
- Why Terraform needs stateError acquiring the state lockTerraform IaC
- Vault
- A tool by HashiCorp for securely storing and managing secrets, encryption keys, and certificates. Vault provides dynamic secrets, automatic rotation, and fine-grained access control, making it a central component of enterprise security architectures.
- Why secrets do not belong in Git
- Volume
- A directory accessible to containers in a Pod, used for persisting data beyond the container's lifecycle. Kubernetes supports many volume types including hostPath, NFS, and cloud provider disks, each with different durability and performance characteristics.
- No space left on deviceKubernetes 101
- Zero-Downtime Deployment
- A deployment strategy where new versions are released without any service interruption to end users. Techniques include rolling updates, blue-green deployments, and canary releases, each of which can keep the service available during the transition, provided new instances receive traffic only once ready and old ones finish in-flight requests before exiting.
- A deploy reports success but users see errors