Docker Quick Reference

A compact lookup for Dockerfile instructions, Compose keys, and the docker and docker compose commands.

Beginner

Before you use this reference

This page is a lookup, not a tutorial. The explanations are in Why Containers, Writing a Dockerfile, Docker Compose Basics, and Building the Data Stack.

Core vocabulary#

Term	Meaning
Image	Immutable package: file system + default command
Container	A running instance of an image
Registry	Where images are stored and pulled (Docker Hub)
Volume	Storage that outlives a container
Bind mount	A host path mounted into a container
Compose project	A set of services managed together from one file

`docker` commands#

Bash

docker run --rm -p 8123:8123 clickhouse/clickhouse-server:latestdocker ps                       # running containersdocker ps -a                    # including stopped onesdocker logs -f <name>           # follow a container's outputdocker exec -it <name> bash     # shell inside a running containerdocker stop <name>              # stop itdocker rm <name>                # remove a stopped containerdocker images                   # local imagesdocker rmi <image>              # remove an imagedocker build -t name:tag .      # build an image from the current directorydocker system prune             # remove stopped containers, unused networks/images

docker run flags:

Flag	Effect
`--rm`	Delete the container when it stops
`-p H:C`	Publish container port `C` on host port `H`
`-e KEY=value`	Set an environment variable
`-v name:/path`	Mount a named volume
`-v ./path:/path`	Bind-mount a host directory
`-d`	Run detached (in the background)
`--name`	Give the container a fixed name

`docker compose` commands#

Bash

docker compose up -d              # start all services in the backgrounddocker compose up -d --build      # rebuild images firstdocker compose ps                 # status of each servicedocker compose logs -f <service>  # follow one service's logsdocker compose exec <service> sh  # shell inside a servicedocker compose build              # build images for services with `build:`docker compose stop               # stop containers, keep themdocker compose start              # start stopped containersdocker compose restart <service>  # restart one servicedocker compose down               # stop and remove containers + networkdocker compose down -v            # also delete named volumes (wipes data)docker compose config             # print the resolved, merged config

Dockerfile instructions#

DOCKERFILE

FROM image:tag            # base image; always pin the tagUSER name                 # user for later instructions and the containerRUN command               # run at build time; each RUN is a cached layerCOPY src dst              # copy from the build context into the imageENV KEY=value             # environment variable baked into the imageWORKDIR /path             # working directory for later instructionsEXPOSE 8080               # documents a port (does not publish it)CMD ["executable", "arg"] # default command when the container startsENTRYPOINT ["executable"] # fixed command; CMD becomes its arguments

Layer-cache rule: order instructions least-changed first. Install system and Python packages before COPY-ing source.

Compose file keys#

YAML

services:  name:    image: repo/name:tag         # OR    build: .                     # build from ./Dockerfile    container_name: name         # fixed name instead of the generated one    command: ["..."]             # override the image's default command    ports:      - "HOST:CONTAINER"    environment:      - KEY=value                # list form      KEY: value                 # OR map form    volumes:      - named_volume:/in/container      - ./host/path:/in/container    depends_on:      other:        condition: service_healthy    healthcheck:      test: ["CMD-SHELL", "curl -f http://localhost:8080/health || exit 1"]      interval: 10s      timeout: 5s      retries: 5      start_period: 30s    restart: always              # always | unless-stopped | "no"
volumes:  named_volume:                  # declare every named volume here

Networking rule#

Talking from	Use address
Your machine	`localhost:<published-host-port>`
One container to another	`<service-name>:<container-port>`

Inside a container, localhost is that container, not the host or another service.

Volumes#

Kind	Source	Deleted by	Use for
Named volume	a name under top-level `volumes:`	`docker compose down -v`	database data directories
Bind mount	a host path (`./dags`)	never (it is your file)	source code, config, logs

Common failure to check first#

Symptom	Usual cause
`port is already allocated`	Another process (or a stale container) uses that host port
Service connects then hangs	Wrong host: used `localhost` instead of the service name from a container
Container exits immediately	Its command finished or failed; check `docker compose logs <service>`
Data gone after restart	Path was not on a volume, or `down -v` was run
Healthcheck never passes	Wrong `test` command, or `start_period` too short