Comprehensive reference for Docker, Docker Compose, Kubernetes kubectl, Helm, Terraform, GitHub Actions, and CI/CD basics.
Docker & DevOps Cheatsheet
A comprehensive reference for Docker containers, Docker Compose multi-container services, Kubernetes cluster administration, Helm chart management, Terraform IaC, GitHub Actions CI/CD workflows, and core DevOps pipeline principles.
## Docker Commands
```bash
# Images (Artifacts)
docker images # List local images
docker pull # Pull an image from registry (e.g. Docker Hub)
docker build -t : . # Build image from Dockerfile in current directory (.)
docker rmi # Delete a local image
docker tag # Retag an existing image (for pushing/renaming)
docker push # Push an image to a remote registry
# Containers (Runtimes)
docker ps # List currently running containers
docker ps -a # List all containers (running, stopped, crashed)
docker run -d -p 80:80 # Run container in background (detached) with port forwarding (host:container)
docker run --name # Run a container with a custom name
docker stop # Stop a running container gracefully
docker start # Start a stopped container
docker rm # Delete a container (must be stopped)
docker rm -f $(docker ps -aq) # Force delete ALL local containers!
# Debugging & Management
docker logs # View container logs
docker logs -f # Follow and view container logs in real-time
docker exec -it sh # Execute interactive terminal inside a running container (sh/bash)
docker inspect # View detailed low-level JSON metadata of a container or image
docker stats # View real-time resource utilization (CPU, memory, net, disk)
# Volumes & Networks
docker volume ls # List local volumes
docker volume rm # Delete a volume
docker network ls # List container networks
docker network inspect # Inspect specific network topology
# Cleanup
docker system prune # Delete all unused containers, networks, and dangling images
docker system prune -a --volumes # Deep clean: delete all stopped containers, unused networks, and ALL unused images/volumes!
```
## Docker Compose
```yaml
# docker-compose.yml Syntax Basics
version: "3.8"
services:
web:
build: . # Build from local Dockerfile
ports:
- "80:80"
environment:
- NODE_ENV=production
volumes:
- db-data:/data
volumes:
db-data: # Named persistent volume
```
```bash
docker compose up # Build, create, and start all services in foreground
docker compose up -d # Build, create, and start all services in background (detached)
docker compose down # Stop and delete containers and networks created by up
docker compose down -v # Stop services and DESTROY all associated persistent volumes!
docker compose ps # View status of services managed by Compose file
docker compose logs -f # Follow and view logs of a specific service
docker compose exec sh # Open interactive shell inside service container
docker compose build # Force rebuild services containing build instructions
```
## Kubernetes kubectl
```bash
# Basic Queries & Context
kubectl config get-contexts # List all configured cluster contexts
kubectl config use-context # Switch active cluster context
kubectl get nodes # List all nodes in cluster
kubectl get namespaces # List all namespaces
kubectl get pods -n # List pods in specific namespace (-A for all namespaces)
kubectl get services # List cluster services (with ports/IPs)
kubectl get deployments # List deployments and replica sets
# Debugging Pods
kubectl describe pod # View comprehensive low-level event logs and configurations of a pod
kubectl logs # View output logs of a pod
kubectl logs -f # Follow and view logs of a pod in real-time
kubectl exec -it -- sh # Open interactive shell inside a running pod container
# Applying & Changing Resources
kubectl apply -f manifest.yaml# Apply or update resources declared in a YAML configuration file
kubectl delete -f manifest.yml# Delete resources defined in a YAML configuration file
kubectl delete pod # Delete a specific pod (replica controller will re-create it)
kubectl scale deploy --replicas=5 # Scale deployment dynamically to 5 replica pods
kubectl rollout status deploy # Monitor deployment rollout progress/status
kubectl rollout undo deploy # Rollback deployment to the previous version
```
## Helm (Kubernetes Package Manager)
```bash
# Repository Management
helm repo add # Add a remote Helm chart repository
helm repo update # Fetch and sync the latest charts from all repositories
helm search repo # Search configured repositories for charts
# Deployments & Releases
helm list # List all releases in the active namespace (-A for all namespaces)
helm install # Install a chart release on the cluster
helm install -f values.yaml # Install chart overriding configurations with custom values file
helm upgrade # Upgrade an existing release to a new version or values config
helm rollback # Rollback a release to a specific revision number
helm uninstall # Uninstall and delete a release from the cluster
helm status # View status details and instructions of a release
```
## Terraform (Infrastructure as Code)
```bash
# Configuration Lifecycle
terraform init # Initialize directory: download providers and backend modules
terraform validate # Validate syntax and configuration integrity of TF files
terraform fmt # Automatically format all TF files according to canonical style
terraform plan # Generate and review execution plan: view what will be created/changed/deleted
terraform plan -out=plan.tfplan # Save execution plan safely to a file
terraform apply # Execute plan and provision real infrastructure resources
terraform apply plan.tfplan # Apply a pre-generated saved execution plan file
terraform destroy # Tear down and destroy all infrastructure provisioned by this folder
# State Management
terraform state list # List all tracked resources in active Terraform state
terraform state show # Show detailed state metadata of a specific tracked resource
terraform refresh # Sync local state file with actual real-world infrastructure
```
## GitHub Actions
```yaml
# .github/workflows/ci.yml Syntax Basics
name: CI Pipeline
on:
push:
branches: [ main ] # Trigger on pushes to main branch
pull_request:
branches: [ main ] # Trigger on PRs targeting main branch
jobs:
build-and-test:
runs-on: ubuntu-latest # Hosted runner environment
steps:
- name: Checkout Code
uses: actions/checkout@v4
- name: Setup Node
uses: actions/setup-node@v4
with:
node-version: 18
- name: Install & Test
run: |
npm install
npm run test
env:
DATABASE_URL: $ # Decrypt repository secret variables
```
## CI/CD Basics
```markdown
Continuous Integration (CI)
- The practice of frequently merging code changes into a shared central repository.
- Core Goal: Detect bugs early and ensure codebase stability.
- Core Steps: Automated Checkout -> Dependency Install -> Linter -> Automated Unit Tests -> Build Compilation.
Continuous Delivery (CD)
- Code is automatically tested, built, and staged for release.
- Deployment to production requires a manual approval trigger.
Continuous Deployment (CD)
- Code changes pass through the entire pipeline and are automatically deployed to production with zero manual gates.
Key Indicators & Practices
- Fast feedback loops (pipelines should complete under 10 minutes).
- Build artifacts once (use the same container image/archive across Test, Staging, and Production environments).
- Blue-Green Deployments: Deploying new version to an identical parallel environment (Green) and flipping traffic instantly to avoid downtime.
- Canary Deployments: Incrementally rolling out updates to a small fraction of users first to mitigate risk.
```
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