Cloud & DevOps Glossary
Plain-English definitions for 46 DevOps, Kubernetes, and cloud infrastructure terms.
A
AKS
Azure Kubernetes Service (AKS) is Microsoft's managed Kubernetes service, where Azure runs the control plane and you manage worker node pools. The Free tier has no cluster management charge but no financially backed uptime SLA, while Standard and Premium add an SLA. You pay for the node VMs and related resources in all tiers.
Alertmanager
Alertmanager receives alerts from Prometheus (and other sources), deduplicates them, groups related alerts, applies routing rules, and sends notifications to the correct receiver, Slack, PagerDuty, email, OpsGenie, or custom webhooks.
Ansible
Ansible is an agentless IT automation tool that uses YAML playbooks to describe automation tasks. It connects to target systems over SSH (or WinRM for Windows) and executes tasks idempotently, running the playbook multiple times produces the same result.
ArgoCD
ArgoCD is a Kubernetes-native GitOps tool that continuously monitors Git repositories and automatically applies any configuration changes to the cluster. It provides a UI, CLI, and API for managing application deployments declaratively.
C
CI/CD
CI/CD stands for Continuous Integration and Continuous Delivery (or Deployment). CI automatically builds and tests every code commit. CD extends this by automatically deploying validated builds to staging or production environments.
ClickOps
ClickOps refers to the practice of creating and configuring cloud infrastructure manually through web consoles (AWS Console, Azure Portal, GCP Console) rather than through code. It is fast to start but creates drift, undocumented configuration, and no rollback path.
ConfigMap and Secret
A ConfigMap stores non-sensitive configuration data (environment variables, config files) as key-value pairs. A Secret stores sensitive data (passwords, API keys, certificates) in base64-encoded form. Both can be injected into pods as environment variables or mounted as files.
D
DaemonSet
A DaemonSet ensures exactly one pod instance runs on every node (or a node subset) in a Kubernetes cluster. New nodes automatically get the pod; removed nodes lose it. Used for infrastructure services that must run cluster-wide.
DevOps
DevOps is a cultural and technical movement that breaks down silos between development and operations teams, enabling faster, more reliable software delivery through automation, shared responsibility, and continuous feedback.
Distributed Tracing
Distributed tracing records the path of a request through a distributed system. Each service adds spans (start time, duration, metadata) to a shared trace, propagated between services in headers. The result is a waterfall view showing where time is spent and where errors occur.
Docker
Docker is a containerisation platform that packages applications and their dependencies into a container image. Containers run as isolated processes on any machine with the Docker runtime, ensuring the application behaves identically in development, CI, and production.
F
Fargate
AWS Fargate is a serverless compute engine for containers. You do not manage EC2 instances or node groups: you specify CPU and memory requirements for your pod or task, and AWS provisions isolated compute for it. Billing is per second for the vCPU, memory and extra storage provisioned.
Flux GitOps
Flux is a CNCF graduated GitOps project that continuously reconciles Kubernetes cluster state with sources such as Git repositories. It is made of composable controllers and has no built-in UI, so it is driven through Git, the CLI and kubectl.
G
GitHub Actions
GitHub Actions is GitHub's integrated CI/CD and automation platform. Workflows are YAML files in `.github/workflows/` that trigger on repository events (push, PR, schedule). GitHub provides hosted Linux, macOS, and Windows runners; you can also run self-hosted runners.
GitLab CI
GitLab CI/CD is the CI/CD system built into GitLab. Pipelines are defined in `.gitlab-ci.yml` and triggered by Git events. GitLab provides shared runners (SaaS) or self-managed runners, plus a built-in container registry, environments, and approval workflows.
GitOps
GitOps is a set of practices where Git repositories are the single source of truth for declarative infrastructure configuration. Changes are made via pull requests; an automated operator continuously reconciles the actual cluster state with the desired state stored in Git.
GKE
Google Kubernetes Engine (GKE) is Google Cloud's managed Kubernetes service. It offers Autopilot mode, where GKE manages the cluster infrastructure including nodes, and Standard mode, where you configure and manage node pools yourself.
Grafana
Grafana is an open-source platform for querying, visualising, alerting on and exploring metrics, logs and traces. It connects to data sources such as Prometheus (metrics), Loki (logs) and Tempo (traces) and renders dashboards, panels and alerts without application code.
H
Helm Chart
A Helm chart is a collection of Kubernetes manifest templates bundled with a values file. Helm renders the templates with supplied values and applies them to a cluster, making it easy to package, version, and deploy Kubernetes applications with different configurations per environment.
Horizontal Pod Autoscaler
The Kubernetes Horizontal Pod Autoscaler (HPA) automatically adjusts the number of replicas of a scalable workload, such as a Deployment, based on observed metrics. When usage exceeds your target, the HPA adds replicas; when it drops, the HPA removes them.
I
Infrastructure as Code
Infrastructure as Code (IaC) is the practice of defining cloud infrastructure, networks, servers, databases, load balancers, in version-controlled configuration files. Tools like Terraform apply these files to create and manage the infrastructure reproducibly.
Ingress Controller
A Kubernetes Ingress Controller watches Ingress resources and configures a load balancer (nginx, Traefik, AWS ALB) to route external HTTP/HTTPS traffic to the correct service based on hostname and path rules.
Istio
Istio is a CNCF service mesh that uses Envoy proxies, deployed as sidecars or in ambient mode, to handle mTLS between services, traffic splitting, retries, circuit breaking and telemetry without changes to application code.
K
Karpenter
Karpenter is an open-source Kubernetes node autoscaler that watches for unschedulable pods and provisions suitable EC2 capacity to run them. It also consolidates empty or underutilised nodes and replaces drifted or expired ones.
Kubernetes
Kubernetes (K8s) is an open-source system for automating the deployment, scaling, and management of containerised applications. It groups containers into logical units (Pods) and manages them across a cluster of nodes.
Kubernetes Operator
A Kubernetes Operator is a custom controller that uses Custom Resource Definitions (CRDs) to manage complex applications with domain-specific operational knowledge. Operators automate tasks like provisioning, scaling, backups, and upgrades for stateful services.
N
Namespace
A Kubernetes Namespace provides a mechanism for isolating groups of resources within a single cluster. Names of resources must be unique within a namespace but not across namespaces. Namespaces are used to divide cluster resources between multiple teams or environments.
Network Policy
A Kubernetes NetworkPolicy is a set of firewall rules that control ingress and egress traffic for a group of pods. By default, all pods can communicate freely; NetworkPolicies restrict this to only approved connections.
Node Affinity
Node Affinity is a set of rules that constrain which nodes a pod can be scheduled on, based on node labels. It supports required rules (hard, pod cannot schedule if unmet) and preferred rules (soft, scheduler prefers nodes meeting the rule but will place elsewhere if needed).
P
Persistent Volume
A PersistentVolume (PV) is a piece of storage in the cluster provisioned by an administrator or dynamically by a StorageClass. A PersistentVolumeClaim (PVC) is a pod's request for storage. Volumes persist beyond the pod lifecycle.
Pod Disruption Budget
A Pod Disruption Budget (PDB) ensures a minimum number of pod replicas remain available during voluntary disruptions such as node drains, cluster upgrades, or manual evictions. Without a PDB, draining a node could take all replicas of a service offline.
Prometheus
Prometheus is a CNCF graduated monitoring system that collects metrics by scraping HTTP endpoints at regular intervals, stores them as time-series data, and provides a query language (PromQL) for analysis and alerting.
R
RBAC
Kubernetes RBAC (Role-Based Access Control) controls who can do what in a cluster. Roles define permitted actions on resources; RoleBindings assign Roles to users, groups or service accounts. ClusterRoles can apply cluster-wide; Roles are namespace-scoped.
Resource Requests and Limits
In Kubernetes, resource requests tell the scheduler how much CPU and memory a pod needs (used for placement decisions). Limits cap how much a container can consume. A container exceeding its memory limit can be OOM killed; one approaching its CPU limit is throttled.
S
Sealed Secrets
Sealed Secrets is a Kubernetes controller and CLI tool that encrypts Kubernetes Secret resources into SealedSecret objects using the cluster's public key. SealedSecrets are safe to commit to Git; only the in-cluster controller can decrypt them.
Service Mesh
A service mesh is a dedicated infrastructure layer that manages communication between microservices. It uses sidecar proxies (typically Envoy) injected alongside each service to handle traffic management, mTLS, retries, circuit breaking, and distributed tracing without changing application code.
SLI, SLO, SLA
SLI (Service Level Indicator) is a quantitative measure of service behaviour (e.g. request latency, error rate). SLO (Service Level Objective) is the target value for that metric (e.g. 99.9% of requests under 200ms). SLA (Service Level Agreement) is a contractual commitment with financial or legal consequences for missing the SLO.
StatefulSet
A StatefulSet gives each pod a stable, unique identity (pod-0, pod-1) and a dedicated PersistentVolume. Unlike Deployments where pods are interchangeable, StatefulSet pods have fixed names and dedicated storage, making them suitable for databases and message brokers.
T
Taints and Tolerations
A taint marks a node to repel pods that do not explicitly tolerate it. A toleration on a pod allows it to be scheduled onto tainted nodes. Together they enforce workload isolation, for example, reserving GPU nodes for ML workloads only.
Terraform
Terraform is an open-source IaC tool from HashiCorp that uses a declarative language (HCL) to define cloud infrastructure. It generates an execution plan, shows what will change, and applies changes safely, tracking resource state in a state file.