#title Docker Cheatsheet
#author Stefan Hornburg (Racke)
#lang en
#sorttopics Docker


** Images

*** Building images

{{{
$ docker build -t myimage:0.001 .
}}}

Use a different Dockerfile:

{{{
$ docker build -t myimage:0.001 -f Dockerfile.myimage .
}}}

Skipping cache:

{{{
$ docker build --no-cache -t myimage:0.001 .
}}}

*** Prune images

Delete all images without an associated container:

{{{
$ docker image prune
}}}

*** Inspect images

In order to inspect the images, you may run them as container with a shell command - usually *bash* but *sh* for Alpine based ones:

{{{
$ docker run -it myimage:0.001 bash
}}}

** Containers

*** Run from image

{{{
$ docker run --name sympa -d -i sympa:6.2.48
}}}

Explanation:

 -d :: detached
 -i :: image tag
 --name :: name of the container (optional)

You can instruct Docker to automatically remove the container when it is terminated
by adding the =--rm= flag:

{{{
$ docker run --rm --name sympa -d -i sympa:6.2.48
}}}

Please note that this also removes the logs for the container.

Environment variables can be passed to the container with the =--env= flag:

{{{
$ docker run --env SYMPA_DB_USER=sympa --env SYMPA_DB_PASSWORD=sympa --name sympa -d -i sympa:6.2.48
}}}

*** Remove and prune

**** Remove container

{{{
docker rm sympa
}}}

Please note that the corresponding image isn't affected.

**** Prune containers

Remove all stopped containers:

{{{
$ docker container prune
}}}

Remove all stopped containers older than a day:

{{{
$ docker container prune --filter "until=24h"
}}}

*** Shell on a running container

{{{
$ docker exec -it 593d9b3219c6 bash
}}}

You can also pass environment variables to the command executed in the Docker container:

{{{
$ docker exec -e SPACEWALK_API_USER=admin -e SPACEWALK_API_PASS=nevairbe -it spacewalk /bin/setup-spacecmd.sh
}}}

Note: the flags for the environment preceed the flag for the container.

*** Copy files from/to container

From:

{{{
$ docker cp wp-site:/var/www/html/wp-config.php .
}}}

To:

{{{
$ docker cp  ./setup-spacecmd.sh spacewalk2:/bin
}}}

*** Logs

To see the log messages for the container *nginx*:

{{{
$ docker logs nginx
}}}

However, this shows only the messages without any further information.

You can add the timestamp with the =--timestamps= commandline option:

{{{
$ docker logs --timestamps nginx
}}}

Show the latest 30 entries:

{{{
$ docker logs --tail 30 nginx
}}}

Follow new entries:

{{{
$ docker logs --tail 0 nginx --follow
}}}


** Container Information

*** IP address

To get the IP address of the container *perldancer*:

{{{
$ docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' perldancer
}}}

*** Determine whether a container is running properly

This checks whether the container with the name *sympa* is active **and** running, e.g. not restarting because of a problem with the command it executes on startup.

{{{
$ docker ps -q --filter=name='/sympa$' --filter=status=running
}}}

** Startup problems

 - Missing environment variables, e.g. =MYSQL_ROOT_PASSWORD= for *mysql* container

** Compose

Run containers and detach:

{{{
$ docker-compose up -d
}}}