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	Docker packages software into lightweight, isolated containers, each run from a read-only image.		Docker packages software into lightweight, isolated containers, each run from a read-only image.

	New to Docker? [https://docs.docker.com/get-started/ Get Started] runs your first container~~; the [https://docs.docker.com/reference/cli/docker/ CLI reference] documents every command.~~		New to Docker? [https://docs.docker.com/get-started/ Get Started] runs your first container

	== Basic example: serve a website ==		== Basic example: serve a website ==

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Docker packages software into lightweight, isolated containers, each run from a read-only image.

New to Docker? [https://docs.docker.com/get-started/ Get Started] runs your first container; the [https://docs.docker.com/reference/cli/docker/ CLI reference] documents every command.

== Basic example: serve a website ==

<syntaxhighlight lang="bash" line highlight="2,4" copy>
docker pull nginx # fetch the image
docker run -d --name web -p 8080:80 nginx # start a container from it
docker ps # is it running?
curl localhost:8080 # yes — the nginx welcome page
docker stop web && docker rm web # stop and remove it
</syntaxhighlight>

An '''image''' is a read-only template; a '''container''' is one running instance of it. Containers are throwaway — anything written inside them vanishes when the container is removed, unless kept in a [[#Volumes|volume]].

== Running containers ==

<syntaxhighlight lang="bash" copy>
docker run -it ubuntu bash # interactive terminal
docker run -d --name db postgres:16 # detached, named
docker run -p 8080:80 nginx # host 8080 → container 80
docker run -v ./data:/app/data app # mount a host directory
docker run --rm -it app # remove the container on exit
docker run -e MODE=prod app # set an environment variable
</syntaxhighlight>

{| class="wikitable"
! Flag !! Effect
|-
| <syntaxhighlight lang="bash" inline>-d</syntaxhighlight> || run detached (in the background)
|-
| <syntaxhighlight lang="bash" inline>-it</syntaxhighlight> || interactive terminal (needed for bash)
|-
| <syntaxhighlight lang="bash" inline>-p host:container</syntaxhighlight> || publish a port
|-
| <syntaxhighlight lang="bash" inline>-v host:container</syntaxhighlight> || mount a volume or directory
|-
| <syntaxhighlight lang="bash" inline>--name</syntaxhighlight> || give the container a name
|-
| <syntaxhighlight lang="bash" inline>--rm</syntaxhighlight> || auto-remove once it stops
|-
| <syntaxhighlight lang="bash" inline>-e KEY=value</syntaxhighlight> || set an environment variable
|}

<blockquote>
'''Port order is always host:container''' — <syntaxhighlight lang="bash" inline>-p 8080:80</syntaxhighlight> means your machine's 8080 forwards to the container's 80, not the other way round.
</blockquote>

== Managing containers ==

<syntaxhighlight lang="bash" copy>
docker ps # running containers
docker ps -a # all, including stopped
docker logs -f web # follow the logs
docker exec -it web bash # shell inside a running container
docker cp web:/etc/nginx/nginx.conf . # copy a file out of a container
docker stop web # stop one
docker start web # start an existing (stopped) one
docker rm web # remove a stopped container
</syntaxhighlight>

<blockquote>
'''<syntaxhighlight lang="bash" inline>docker run</syntaxhighlight> always creates a new container.''' Re-run the same task? <syntaxhighlight lang="bash" inline>docker stop</syntaxhighlight> / <syntaxhighlight lang="bash" inline>docker start</syntaxhighlight> the existing one instead — or use [[#Docker Compose|Compose]].
</blockquote>

== Images ==

<syntaxhighlight lang="bash" copy>
docker build -t myapp . # build an image from the Dockerfile
docker images # list local images
docker pull postgres:16 # fetch an image (or a tag)
docker push user/myapp:v1 # upload to a registry
docker tag myapp user/myapp:v1 # retag
docker rmi myapp # remove an image
</syntaxhighlight>

== Dockerfile ==

A plain text recipe that <syntaxhighlight lang="bash" inline>docker build</syntaxhighlight> turns into an image:

<syntaxhighlight lang="dockerfile" copy>
FROM python:3.12-slim # base image
WORKDIR /app # working directory for the rest
COPY requirements.txt . # copy file(s) into the image
RUN pip install -r requirements.txt
COPY . . # everything else
CMD ["python", "app.py"] # default command when run
</syntaxhighlight>

== Volumes ==

<syntaxhighlight lang="bash" copy">
docker run -v ./data:/app/data app # bind mount: a host directory
docker run -v data-vol:/data app # named volume, managed by Docker
docker volume ls # list named volumes
docker volume prune # remove unused ones
</syntaxhighlight>

<blockquote>
'''Without a volume, container data is lost on <syntaxhighlight lang="bash" inline>docker rm</syntaxhighlight>.''' The database keeps its data only because something like <syntaxhighlight lang="bash" inline>-v db-data:/var/lib/postgresql/data</syntaxhighlight> is mounted.
</blockquote>

== Docker Compose ==

Multi-container setups described in YAML — start, stop and rebuild everything with one command:

<syntaxhighlight lang="yaml" copy>
services:
web:
build: . # build from the Dockerfile
ports:
- "8080:80"
volumes:
- ./data:/app/data
db:
image: postgres:16 # or pull a ready-made image
environment:
POSTGRES_PASSWORD: secret
</syntaxhighlight>

<syntaxhighlight lang="bash" copy>
docker compose up -d # start everything in the background
docker compose up --build # rebuild images, then start
docker compose ps # status of all services
docker compose logs -f # follow the combined logs
docker compose down # stop and remove the containers
</syntaxhighlight>

<blockquote>
'''The modern command is <syntaxhighlight lang="bash" inline>docker compose</syntaxhighlight> (space).''' The old v1 tool was a separate binary spelled <syntaxhighlight lang="bash" inline>docker-compose</syntaxhighlight> (hyphen) — you may still see it in older tutorials.
</blockquote>

== Cleanup ==

<syntaxhighlight lang="bash" copy>
docker system prune # dangling images, stopped containers, unused networks and cache
docker system prune -a # ... plus every image no container uses
docker system df # disk usage by images, containers, volumes
</syntaxhighlight>

<blockquote>
'''<syntaxhighlight lang="bash" inline>docker system prune -a</syntaxhighlight> removes images you are not running.''' Images you might want again later need a <syntaxhighlight lang="bash" inline>docker pull</syntaxhighlight> — they are not lost, just re-fetched.
</blockquote>

== Further reading ==

* [https://docs.docker.com/ Docker documentation] — the official docs
* [https://docs.docker.com/get-started/ Get Started] — the recommended tutorial
* [https://docs.docker.com/reference/cli/docker/ Docker CLI reference] — every command and flag
* [https://docs.docker.com/compose/ Compose documentation] — multi-container applications

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Rongzhou at 10:45, 23 August 2026

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