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Docker basic commands.

The almost-always useful stuff!

Warning: in this document the term “image-name” is used instead of “repository-name”

Build

Create a docker image tagged ‘web1’

docker image build -t <image-name>:<image-tag> .

Example:

docker image build -t web1:1.0 .

Show metadata about the image

docker image inspect web1

Show the docker images available locally

docker image ls

Remove and image from cache

You can do in two ways:

  1. Delete by repository name and tag: docker image rm <image-name>:<image-tag>
  2. Delete by image id: docker image rm <image-id-first-4-digits>
docker image rm web1:1.0
  • '-f' forces the image removal, even if it is not dangling (unused)
docker image rm -f 29a4

PS C:\src\docker-fundamentals\src\06-docker-in-the-real-world\03-creating-a-dockerfile-part-1> docker image ls
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
web1                latest              29a488fd263e        2 minutes ago       73.1MB
marioscalas/web1    latest              29a488fd263e        2 minutes ago       73.1MB

Publishing an image to a remote registry (e.g., Docker Hub)

Log into repository:

docker login

docker image tag web1 marioscalas/web1:latest

(In this case 'marioscalas/web1' is the repository name)

Push image to remote registry (the one we logged into)

docker image push marioscalas/web1:latest

We can delete the image and then pull it back

docker image rm marioscalas/web1:latest 
docker image pull marioscalas/web1:latest

Renaming / Retagging an image

Use docker tag to create a new tag for the image and remove the unwanted one:

docker image tag <FROM_TAG:VERSION> <TO_TAG:VERSION>

docker image tag web1:latest marioscalas/web1:latest
docker image rm marioscalas/web1:latest

Run a container

Starting

docker container ls
docker container ls -a

Start a container in interactive mode (colored terminal, CTRL+C is working, ...), bind LOCAL-PORT:CONTAINER-PORT lists (-p) and the environment variable used by the Flask web framework to know which app to run (we can use several '-e' to pass more variables) --rm removes the container after being stopped --name sets a name that we can use in the following commands (instead of the default ones) -d runs the container in daemon mode

Basic:

docker container run -it -p 5000:5000 -e FLASK_APP=app.py web1:latest

Super smart:

docker container run -it --rm --name web1 -p 5000:5000 -e FLASK_APP=app.py -e FLASK_DEBUG=1 -d web1:latest

Mounting external volumes

Use the -v LOCAL-PATH:CONTAINER-PATH

Note: it doesn't seem to like the symlink paths so I've to resort to this.

docker container run -it --rm --name web1 -p 5000:5000 -e FLASK_APP=app.py -e FLASK_DEBUG=1 -d  -v $(readlink -f $PWD):/app web1:latest

Run multiple containers

docker container run -it --rm --name web1_2 -p 5000 -e FLASK_APP=app.py -d web1:latest

Auto-respawning container (restarts automatically if the docker daemon restarts)

docker container run -it --name web1_3 -p 5000 -e FLASK_APP=app.py -d --restart on-failure  web1:latest

Stopping

docker container stop <CONTAINER_NAME_OR_ID>

Note: stopped container are not cleaned up so we have either to do this manually or just provide a flag when starting it:

docker container stop beautiful_heyrovsky

Monitoring container logs and stats

docker container logs -f web1
docker container stats
docker container inspect <CONTAINER-NAME-OR-ID>

Logging into a container and inspecting the FS

docker container exec -it web1 sh

Running custom scripts

You create a script (e.g. docker-entrypoint.sh) and then you add into your Dockerfile something like the following.

Note: we put stuff into the root directory because we want to keep the entrypoint scripts separated from the app code.

COPY docker-entrypoint.sh /
RUN chmod +x /docker-entrypoint.sh
ENTRYPOINT ["/docker-entrypoint.sh"]

CMD ["flask", "run", "--host=0.0.0.0", "--port=5000"]

By default, the ENTRYPOINT instruction will use /bin/sh -c for running whatever is specified in the CMD instruction. So in our script, we are basically overriding the start command with some script that must do something and still run the CMD-stuff!

The script will be run everytime the Docker image is run!

A sample docker-entrypoint.sh:

#!/bin/sh
set -e

echo "The Dockerfile ENTRYPOINT has been executed!"

export WEB2_COUNTER_MSG="${WEB2_COUNTER_MSG:-carbon based life forms have sensed this website}"

exec "$@"

With this script, we can pass different environment variables:

docker container run -it --rm --name webscripted -p 5001:5000 -e FLASK_APP=app.py -e FLASK_DEBUG=1 -e WEB2_COUNTER_MSG="Docker fans have visited this page" --net firstnetwork -v $(readlink -f $PWD):/app webscripted:latest

In this way we can set defaults in the script and override them with command line (e.g., perform database migrations).

Docker clean up and troubleshooting

How much space are we consuming with our images?

docker system df
TYPE                TOTAL               ACTIVE              SIZE                RECLAIMABLE
Images              18                  0                   618.7MB             618.7MB (100%)
Containers          0                   0                   0B                  0B
Local Volumes       1                   0                   98B                 98B (100%)
Build Cache         0                   0                   0B                  0B

This also dumps volumes and other things:

docker system df -v

Cleaning up dangling stuff and more

Every image with is safe to delete

docker image ls

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
webscripted         latest              6e3fc5d5cf52        32 minutes ago      110MB
weboptimized        latest              e6163879bd04        48 minutes ago      103MB
web3                latest              145f2ff1de1d        About an hour ago   110MB
<none>              <none>              a069e54648e9        10 hours ago        110MB
web2                latest              52e0ea46548b        11 hours ago        110MB
web1                latest              ec34627d584b        14 hours ago        73.1MB
<none>              <none>              69688ef2c78a        14 hours ago        73.1MB
...

We can remove unused resources:

docker system prune -f

Or remove everything we have locally:

docker system prune -f -a

Report your system configuration

docker system info

Stopping all running containers at once

docker container stop $(docker container ls -aq)