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Kubernetes Essentials

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Pods, deployments, services, and core Kubernetes concepts.

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Kubernetes

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1Kubernetes
Open-source container orchestration platform for automating deployment, scaling, and management of containerized applications. Created by Google, now maintained by CNCF
2Pod
Smallest deployable unit in Kubernetes. Contains one or more containers that share network namespace and storage volumes. Containers in a pod always run on same node
3Node
Worker machine (VM or physical) that runs containerized applications. Each node contains: kubelet (agent), container runtime (Docker/containerd), kube-proxy (networking)
4Cluster
Set of nodes managed by Kubernetes. Consists of: Control Plane (master) managing the cluster, and Worker Nodes running the actual applications
5Control Plane
Master node components: API Server (front-end), etcd (key-value store), Scheduler (assigns pods to nodes), Controller Manager (maintains desired state), Cloud Controller Manager
6Kubectl
Command-line tool for interacting with Kubernetes clusters: kubectl get pods kubectl apply -f deployment.yaml kubectl describe pod <name> kubectl logs <pod>
7Deployment
Declarative way to manage a set of identical pods. Provides rolling updates, rollbacks, scaling. Manages ReplicaSets automatically. Most common way to run stateless applications
8ReplicaSet
Ensures specified number of pod replicas are running at any time. If pod fails, ReplicaSet creates replacement. Usually managed by Deployment (don't create directly)
9Service
Stable network endpoint for a set of pods. Provides load balancing and service discovery. Types: ClusterIP (internal), NodePort (external port), LoadBalancer (cloud LB), ExternalName
10ClusterIP, NodePort, vs LoadBalancer
ClusterIP: internal only, default, virtual IP within cluster NodePort: exposes service on static port on each node (30000-32767) LoadBalancer: provisions external load balancer (cloud provider)
11Namespace
Virtual cluster for resource isolation and multi-tenancy. Organizes resources (dev/staging/prod). Default namespaces: default, kube-system, kube-public, kube-node-lease
12ConfigMap
Stores non-confidential configuration data as key-value pairs. Can be consumed as environment variables, command-line args, or config files in volumes. Decouples config from container images
13Secret
Like ConfigMap but for sensitive data (passwords, tokens, keys). Base64 encoded (NOT encrypted by default). Can be mounted as volumes or env vars. Use encryption at rest in production
14Volume
Directory accessible to containers in pod. Types: emptyDir (temp), hostPath (node filesystem), persistentVolumeClaim, configMap, secret, nfs, cloud storage (EBS, GCE Persistent Disk)
15PersistentVolume (PV) and PersistentVolumeClaim (PVC)
PV: cluster resource provisioned by admin (storage) PVC: request for storage by user (consumes PV) Abstracts storage details. Decouples storage from pod lifecycle
16StatefulSet
For stateful applications requiring stable network identity and persistent storage. Provides ordered deployment/scaling, stable pod names (pod-0, pod-1), persistent storage per pod. Use for databases
17DaemonSet
Ensures pod runs on all (or selected) nodes. Automatically adds pods to new nodes. Common uses: monitoring agents, log collectors, node-level tools. Example: Fluentd, Prometheus node exporter
18Job
Creates one or more pods for batch workload that run to completion. Ensures specified number of successful completions. Pods are not restarted after success. Use for one-off tasks
19CronJob
Creates Jobs on a schedule (like cron). Syntax: "*/5 * * * *" (every 5 minutes). Good for periodic tasks: backups, reports, cleanup jobs
20Ingress
HTTP(S) routing to services from outside cluster. Provides: URL-based routing, SSL/TLS termination, name-based virtual hosting. Requires Ingress Controller (nginx, traefik, HAProxy)
21Ingress Controller
Implements Ingress resource. Reads Ingress rules and configures load balancer accordingly. Popular: nginx-ingress, traefik, HAProxy, Istio. Must be installed separately
22Label
Key-value pair attached to objects (pods, services, nodes). Used for organizing and selecting resources: app=frontend environment=production Selectors query by labels
23Selector
Query to select resources by labels: Equality-based: app=frontend Set-based: environment in (prod, staging) Used by Services to target pods, by ReplicaSets to manage pods
24Annotation
Like labels but for non-identifying metadata. Not used for selection. Store build info, timestamps, contact details, tool configurations. Can be larger than labels
25Deployment vs StatefulSet
Deployment: stateless apps, pods are interchangeable, random names, no ordering StatefulSet: stateful apps, stable identity, ordered deployment (0,1,2...), persistent storage per pod
26Horizontal Pod Autoscaler (HPA)
Automatically scales number of pods based on CPU/memory usage or custom metrics. Example: maintain 70% CPU utilization. Requires metrics-server
27Vertical Pod Autoscaler (VPA)
Adjusts CPU and memory requests/limits for pods based on usage. Helps right-size resources. Can run in recommendation mode or auto mode (recreates pods with new limits)
28Liveness Probe
Checks if container is running. If fails, kubelet kills and restarts container. Types: HTTP GET, TCP Socket, Exec command. Prevents stuck processes
29Readiness Probe
Checks if container is ready to serve traffic. If fails, endpoints removed from Service. Pod stays alive but doesn't receive traffic. Use during startup or maintenance
30Startup Probe
Checks if application has started. Disables liveness/readiness checks until startup succeeds. Good for slow-starting containers. Prevents premature kill during initialization