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--- wiki:ai:docker_cheatsheet [2025/12/20 00:37] – created ymurugesan
+++ wiki:ai:docker_cheatsheet [2026/01/21 22:00] (current) – bgourley
@@ Line 1: / Line 1: @@
-Docker cheatsheet
+======Docker Basics – Command Reference======
+====Docker Installation and Health Checks====
+**docker version**
+Purpose\\
+Verifies that the Docker CLI is installed and whether it can communicate with the Docker daemon.
+What it shows\\
+Client version information and server (daemon) version information.
+Usage
+docker version
+Notes\\
+If the Docker daemon is not running, only client information is shown and the server section fails.
+**docker info**
+Purpose\\
+Displays detailed system-wide Docker configuration and runtime information.
+What it shows\\
+Docker root directory, storage driver, number of images and containers, OS and architecture details.
+Usage
+docker info
+====Working With Containers====
+**docker run**
+Purpose\\
+Creates and starts a new container from an image.
+Common usage
+docker run hello-world
+docker run -it ubuntu bash
+docker run -d --name my-nginx -p 8080:80 nginx
+Key options\\
+-it runs the container interactively\\
+-d runs the container in the background\\
+--name assigns a readable name to the container\\
+-p maps host ports to container ports
+**docker ps**
+Purpose\\
+Lists containers.
+Usage
+docker ps
+docker ps -a
+docker ps shows running containers only.\\
+docker ps -a includes stopped containers.
+**docker stop and docker start**
+Purpose\\
+Stops or starts an existing container.
+Usage
+docker stop my-container
+docker start my-container
+**docker rm**
+Purpose\\
+Removes a stopped container.
+Usage
+docker rm my-container
+**docker inspect**
+Purpose\\
+Displays low-level JSON metadata for containers or images.
+Typical use cases\\
+Inspect environment variables, network settings, mounts, ports, and runtime configuration.
+Usage
+docker inspect my-container
+====Executing Commands in Running Containers====
+**docker exec**
+Purpose\\
+Runs a command inside a running container.
+Interactive shell
+docker exec -it my-container bash
+docker exec -it my-container sh
+One-off command
+docker exec my-container ls /etc
+====Logs and Runtime Monitoring====
+**docker logs**
+Purpose\\
+Displays standard output and error logs from a container.
+Usage
+docker logs my-container
+docker logs -f my-container
+docker logs --tail 50 my-container
+**docker stats**
+Purpose\\
+Shows real-time CPU, memory, network, and disk usage for containers.
+Usage
+docker stats
+docker stats my-container
+====Images and Registries====
+**docker pull**
+Purpose\\
+Downloads an image from a container registry.
+Usage
+docker pull ubuntu
+docker pull nvcr.io/nvidia/pytorch:24.04-py3
+**docker images**
+Purpose\\
+Lists all locally available images.
+Usage
+docker images
+**docker tag**
+Purpose\\
+Creates an additional name and tag for an image, commonly used before pushing to a registry.
+Usage
+docker tag nginx myuser/nginx:demo
+**docker push**
+Purpose\\
+Uploads an image to a container registry.
+Usage
+docker push myuser/nginx:demo
+Prerequisite\\
+You must authenticate with the registry using docker login.
+====Cleanup and Disk Management====
+**docker system df**
+Purpose\\
+Displays Docker disk usage information.
+Usage
+docker system df
+**docker container prune**
+Purpose\\
+Removes all stopped containers.
+Usage
+docker container prune
+**docker image prune**
+Purpose\\
+Removes dangling and unused images.
+Usage
+docker image prune
+**docker system prune**
+Purpose\\
+Removes unused containers, networks, images, and build cache.
+Usage
+docker system prune
+Aggressive cleanup
+docker system prune -a --volumes
+This removes all unused images and volumes and should be used with caution.
+====Docker Contexts====
+**docker context ls**
+Purpose\\
+Lists available Docker contexts such as local, desktop, or remote environments.
+Usage
+docker context ls
+**docker context use**
+Purpose\\
+Switches the active Docker context.
+Usage
+docker context use desktop-linux
+======Docker Networking Basics======
+====Docker Network Types====
+**Default bridge network**
+Purpose\\
+Provides a private, NATed network for containers. Containers attached to the same bridge network can communicate using IP addresses. Name-based DNS resolution is limited on the default bridge.
+Notes\\
+This is the network used when no --network flag is specified.
+Inspect the default bridge
+docker network inspect bridge
+Run a container on the default bridge
+docker run --rm alpine sh
+**Host network**
+Purpose\\
+Shares the host network stack with the container.
+Notes\\
+On macOS, Docker runs inside a virtual machine. As a result, --network host does not behave the same way it does on Linux and does not give direct access to the Mac’s network namespace.
+Run a container with host networking
+docker run --rm --network host alpine sh
+**None network**
+Purpose\\
+Disables all networking for the container except the loopback interface.
+Run a container with no networking
+docker run --rm --network none alpine sh
+====Managing Docker Networks====
+**docker network ls**
+Purpose\\
+Lists all Docker networks.
+Usage
+docker network ls
+**docker network inspect**
+Purpose\\
+Displays detailed configuration and connected containers for a network.
+Usage
+docker network inspect ai-net
+**docker network create**
+Purpose\\
+Creates a user-defined bridge network with built-in DNS resolution and isolation.
+Usage
+docker network create ai-net
+Notes\\
+User-defined bridge networks are recommended for multi-container applications.
+**docker network rm**
+Purpose\\
+Deletes a Docker network.
+Usage
+docker network rm ai-net
+====Running Containers on Networks====
+**Run container on a specific network**
+Purpose\\
+Attaches a container to a specified network at startup.
+Usage
+docker run -d --name web --network ai-net nginx
+**docker network connect**
+Purpose\\
+Connects an existing container to an additional network.
+Usage
+docker network connect other-net web
+Notes\\
+Containers can be attached to multiple networks simultaneously.
+**Container DNS Resolution**
+Purpose\\
+Allows containers on the same user-defined bridge network to resolve each other by name using Docker’s embedded DNS server.
+Test DNS resolution
+docker run --rm -it --network ai-net alpine sh -c "apk add --no-cache bind-tools && nslookup web"
+Inspect DNS configuration inside a container
+docker exec -it web cat /etc/resolv.conf
+Add a network alias
+docker network connect --alias websvc ai-net web
+**Port Publishing and Exposure**
+**-p flag**
+Purpose\\
+Publishes a container port to the host, enabling host-to-container communication.
+Syntax
+-p <host_port>:<container_port>
+Example
+docker run -d --name web -p 8080:80 nginx
+Verify published ports
+docker ps
+docker port web
+Notes\\
+Port publishing is not required for container-to-container communication on the same Docker network.
+====Container-to-Container Communication====
+**Same network communication**
+Purpose\\
+Allows containers on the same network to communicate without published ports.
+Test connectivity
+docker run --rm -it --network ai-net nicolaka/netshoot sh -c "curl -I http:%%//%%web"
+**Cross-network isolation**
+Purpose\\
+Demonstrates that containers on different networks cannot communicate by default.
+Test isolation
+docker run --rm -it --network other-net nicolaka/netshoot sh -c "curl -I http:%%//%%web || echo 'unreachable'"
+Connect container to multiple networks
+docker network connect other-net web
+Re-test connectivity
+docker run --rm -it --network other-net nicolaka/netshoot sh -c "curl -I http:%%//%%web"
+====Networking Diagnostics and Debugging====
+**Inspect container network settings**
+Purpose\\
+Displays IP addresses, networks, and endpoints for a container.
+Usage
+docker inspect web
+**Use a diagnostic container**
+Purpose\\
+Provides networking tools such as curl, ping, nslookup, and traceroute.
+Usage
+docker run --rm -it --network ai-net nicolaka/netshoot
+====Cleanup Networking Resources====
+**Remove containers**
+docker rm -f web client
+**Remove networks**
+docker network rm ai-net test-net other-net
+======Docker Volumes and Storage======
+====Volumes vs Bind Mounts vs tmpfs====
+**Concept Summary**
+Named volume
+  * Managed by Docker
+  * Lives in Docker’s storage area
+  * Best for persistent application data
+Bind mount
+  * Maps a host directory into the container
+  * Best for development and live code editing
+tmpfs
+  * In-memory filesystem
+  * Data is lost when the container stops
+  * Best for temporary or sensitive data
+**Named volume example**
+Create a named volume:
+docker volume create myvol
+docker volume ls
+docker volume inspect myvol
+Run a container using the volume:
+docker run --rm -it -v myvol:/data alpine sh
+Inside the container:
+echo "hello from volume" > /data/file.txt
+ls /data
+exit
+Run another container with the same volume:
+docker run --rm -it -v myvol:/data alpine sh
+Inside:
+cat /data/file.txt
+exit
+What this demonstrates
+  * The volume persists after the first container exits.
+  * A second container can read the same data.
+  * Data is independent of any specific container.
+**Bind mount example (host directory)**
+Create a directory on the host:
+mkdir -p ~/docker-bind-test
+echo "hello from host" > ~/docker-bind-test/host.txt
+Run a container with a bind mount:
+docker run --rm -it \
+-v ~/docker-bind-test:/data \
+alpine sh
+Inside the container:
+ls /data
+echo "written from container" > /data/container.txt
+exit
+On the host:
+ls ~/docker-bind-test
+cat ~/docker-bind-test/container.txt
+What this demonstrates
+  * The container sees and modifies the host filesystem directly.
+  * Changes on the host and in the container are immediately visible.
+  * No rebuild is required to reflect code or data changes.
+**tmpfs example (in-memory)**
+Run a container with tmpfs:
+docker run --rm -it \
+--tmpfs /data:rw,size=64m \
+alpine sh
+Inside:
+echo "temp data" > /data/tmp.txt
+ls /data
+exit
+Run a new container:
+docker run --rm -it --tmpfs /data alpine sh -c "ls /data || echo empty"
+What this demonstrates
+  * Data stored in tmpfs disappears when the container stops.
+  * Data never touches disk.
+  * Storage is purely in memory.
+====Create and Manage Named Volumes====
+**Create and list volumes**
+docker volume create ai-data
+docker volume ls
+**Inspect volume metadata**
+docker volume inspect ai-data
+Look for:
+  * Driver type (usually local)
+  * Mountpoint inside Docker’s storage
+**Use a volume and verify persistence**
+Write data into the volume:
+docker run --rm -it -v ai-data:/models alpine sh
+Inside:
+echo "model checkpoint v1" > /models/checkpoint.txt
+exit
+Verify persistence:
+docker run --rm -it -v ai-data:/models alpine sh -c "cat /models/checkpoint.txt"
+What this demonstrates
+  * Data written by one container is visible to future containers.
+  * Volumes persist beyond container lifetimes.
+====Use Bind Mounts for Development====
+**Create a simple development file**
+On the host:
+mkdir -p ~/bind-dev
+cat > ~/bind-dev/app.py << 'EOF'
+print("version 1")
+EOF
+Run a Python container with bind mount:
+docker run --rm -it \
+-v ~/bind-dev:/app \
+python:3.12-slim \
+python /app/app.py
+Edit the file on the host:
+echo 'print("version 2")' >> ~/bind-dev/app.py
+Re-run the container:
+docker run --rm -it \
+-v ~/bind-dev:/app \
+python:3.12-slim \
+python /app/app.py
+What this demonstrates
+  * The container runs code directly from the host filesystem.
+  * Code changes do not require rebuilding an image.
+  * Ideal for iterative development workflows.
+====Share Volumes Between Containers====
+**Create a shared volume**
+docker volume create shared-vol
+**Writer container**
+Run:
+docker run --rm -it -v shared-vol:/shared alpine sh
+Inside:
+echo "written by writer" > /shared/data.txt
+exit
+**Reader container**
+Run:
+docker run --rm -it -v shared-vol:/shared alpine sh
+Inside:
+cat /shared/data.txt
+exit
+What this demonstrates
+  * Multiple containers can mount the same volume.
+  * Data written by one container is immediately available to others.
+  * Enables multi-stage pipelines and producer–consumer patterns.
+====Back Up and Restore Volume Data====
+**Back up a volume to a tar archive**
+Create a backup:
+docker run --rm \
+-v ai-data:/data \
+-v $(pwd):/backup \
+alpine \
+tar czf /backup/ai-data-backup.tar.gz -C /data .
+Verify:
+ls ai-data-backup.tar.gz
+What this does
+  * Mounts the volume at /data
+  * Mounts the current host directory at /backup
+  * Archives all volume contents into a file on the host
+**Simulate data loss**
+Delete and recreate the volume:
+docker volume rm ai-data
+docker volume create ai-data
+Check it is empty:
+docker run --rm -it -v ai-data:/models alpine sh -c "ls /models"
+**Restore from backup**
+Restore the data:
+docker run --rm \
+-v ai-data:/data \
+-v $(pwd):/backup \
+alpine \
+tar xzf /backup/ai-data-backup.tar.gz -C /data
+Verify:
+docker run --rm -it -v ai-data:/models alpine sh -c "cat /models/checkpoint.txt"
+What this demonstrates
+  * Volume data can be fully backed up and restored.
+  * Volumes are portable across machines and environments.
+====Clean Up Unused Volumes====
+**List volumes**
+docker volume ls
+**Remove specific volumes**
+docker volume rm myvol shared-vol ai-data
+**Remove all unused volumes**
+docker volume prune
+**Inspect disk usage**
+docker system df -v
+What this demonstrates
+  * Volumes consume real disk space.
+  * Unused volumes accumulate over time.
+  * Regular cleanup prevents silent disk exhaustion.
+======Docker Compose======
+====Overview====
+This reference documents the core Docker Compose commands used to:
+  * Build and run multi-container applications
+  * Manage service dependencies
+  * Configure health checks
+  * Use environment files
+  * Control application lifecycle
+  * Scale services horizontally
+All commands assume:
+  * macOS with Docker Desktop
+  * Docker Compose v2 (docker compose)
+  * A project directory containing docker-compose.yml
+====Project Setup Commands====
+**mkdir and cd**
+Purpose\\
+Creates and enters a new project directory for a Compose application.
+Usage
+mkdir compose-lab && cd compose-lab
+mkdir app
+What it does
+  * Creates a folder to hold all Compose-related files
+  * Groups all containers, networks, and volumes under a single project name
+  * Makes lifecycle management easier
+====Docker Compose Lifecycle Commands====
+**docker compose up**
+Purpose\\
+Builds images (if needed) and starts all services defined in docker-compose.yml.
+Usage
+docker compose up
+docker compose up -d
+docker compose up -d --build
+Options
+  * -d runs services in the background (detached mode)
+  * --build forces a rebuild of images before starting
+What it does
+  * Creates a default network for the project
+  * Creates named volumes if missing
+  * Builds images for services with build:
+  * Starts containers in dependency order
+  * Attaches logs to the terminal (unless -d is used)
+When to use
+  * Initial startup of the stack
+  * After code or Dockerfile changes
+  * For local testing and dev environments
+**docker compose down**
+Purpose\\
+Stops and removes all services in the Compose project.
+Usage
+docker compose down
+docker compose down -v
+docker compose down --rmi local -v
+Options
+  * -v removes named volumes (destroys persistent data)
+  * --rmi local removes images built by Compose
+What it does
+  * Stops all running containers
+  * Deletes containers
+  * Deletes the project network
+  * Optionally deletes volumes and images
+When to use
+  * Resetting the environment
+  * Freeing system resources
+  * Recreating a clean stack
+**docker compose ps**
+Purpose\\
+Lists the current status of services in the Compose project.
+Usage
+docker compose ps
+What it does
+  * Shows container names
+  * Displays service states (running, exited, unhealthy)
+  * Shows port mappings
+  * Displays health status
+When to use
+  * Verify everything is running
+  * Debug startup failures
+  * Check healthcheck status
+**docker compose logs**
+Purpose\\
+Displays logs from all services in the project.
+Usage
+docker compose logs
+docker compose logs -f
+docker compose logs api
+Options
+  * -f follows logs in real time
+  * api limits output to a single service
+What it does
+  * Aggregates stdout and stderr from all containers
+  * Prefixes logs with service names
+  * Streams logs live when -f is used
+When to use
+  * Debug startup issues
+  * Monitor API or database activity
+  * Investigate crashes or errors
+====Build and Image Management====
+**docker compose build**
+Purpose\\
+Builds images for services that specify a build: section.
+Usage
+docker compose build
+docker compose build api
+What it does
+  * Runs docker build for each service image
+  * Tags images with project-specific names
+  * Caches build layers between runs
+When to use
+  * Pre-build images before starting services
+  * Debug Dockerfile changes
+  * Speed up later docker compose up runs
+====Service Interaction Commands====
+**docker compose exec**
+Purpose\\
+Runs a command inside a running service container.
+Usage
+docker compose exec api sh
+docker compose exec db psql -U composeuser compose_db
+What it does
+  * Executes a command in the target container
+  * Attaches stdin/stdout for interactive use
+  * Uses the existing running container
+When to use
+  * Debug inside containers
+  * Inspect environment variables
+  * Run admin tools (psql, bash, python)
+**docker compose stop**
+Purpose\\
+Stops services without removing containers.
+Usage
+docker compose stop
+docker compose stop db
+What it does
+  * Sends a stop signal to containers
+  * Keeps containers, networks, and volumes intact
+When to use
+  * Temporarily pausing services
+  * Simulating outages
+  * Preserving state for later restart
+**docker compose start**
+Purpose\\
+Restarts stopped services.
+Usage
+docker compose start
+docker compose start db
+What it does
+  * Restarts previously stopped containers
+  * Preserves container filesystem and volumes
+When to use
+  * Resuming paused services
+  * Testing recovery behavior
+  * Bringing a stack back online
+====Health and Inspection Commands====
+**docker inspect**
+Purpose\\
+Displays low-level metadata about a container.
+Usage
+docker inspect compose-db
+docker inspect compose-api
+What it does
+  * Shows container config, networks, volumes
+  * Displays health status and logs
+  * Reveals failure reasons for unhealthy services
+When to use
+  * Debug healthcheck failures
+  * Inspect network wiring
+  * Validate volume mounts
+**docker compose exec env**
+Purpose\\
+Displays environment variables inside a container.
+Usage
+docker compose exec api env | sort
+What it does
+  * Prints all environment variables
+  * Confirms .env and env_file values are injected
+When to use
+  * Validate runtime configuration
+  * Debug missing credentials
+  * Confirm DB host/port values
+====Service Scaling====
+**docker compose up --scale**
+Purpose\\
+Runs multiple instances of a service.
+Usage
+docker compose up -d --scale api=3
+What it does
+  * Starts additional containers for the service
+  * Names them sequentially (api-1, api-2, api-3)
+  * Attaches all replicas to the same network
+When to use
+  * Simulate horizontal scaling
+  * Test concurrency handling
+  * Prepare for load balancing setups
+Important limitation\\
+Compose does not automatically load-balance traffic across replicas.\\
+A reverse proxy (nginx, Traefik) is required for real traffic distribution.
+====Networking and Port Mapping====
+**curl http:%%//%%localhost:8080**
+Purpose\\
+Tests connectivity from the host into a containerized service.
+Usage
+curl http:%%//%%localhost:8080/healthz
+curl http:%%//%%localhost:8080/readyz
+What it does
+  * Sends HTTP request to host port 8080
+  * Docker forwards traffic into the API container
+  * Validates networking and service health
+When to use
+  * Smoke testing APIs
+  * Validating port publishing
+  * Debugging networking issues
+====Cleanup and Reset Commands====
+**docker compose down -v**
+Purpose\\
+Destroys the entire Compose environment including volumes.
+Usage
+docker compose down -v
+What it does
+  * Stops all containers
+  * Deletes containers
+  * Deletes networks
+  * Deletes named volumes
+  * Wipes database and persistent state
+When to use
+  * Full environment reset
+  * Freeing disk space
+  * Starting fresh
+**docker compose down --rmi local -v**
+Purpose\\
+Removes everything created by Compose including images.
+Usage
+docker compose down --rmi local -v
+What it does
+  * Stops services
+  * Deletes containers
+  * Deletes networks
+  * Deletes volumes
+  * Deletes built images
+When to use
+  * Total teardown
+  * Reclaiming disk space
+  * Forcing clean rebuilds

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