Docker References

This document provides bare minimum references to Docker and Docker Compose to get started in working environment. If extra information is required then it is recommended to check the official Docker documentations.

Docker Basic Commands

1. Pulling image from Docker Hub

Usage

$ docker pull image:tag

Example

$ docker pull ruby:2.7-alpine
2.7-alpine: Pulling from library/ruby
4c0d98bf9879: Pull complete 
e5fcc264663b: Pull complete 
1c151e279a03: Pull complete 
ff2cf7ba9ddf: Pull complete 
773be079cf77: Pull complete 
Digest: sha256:7524541d03ceacaccc8da4721681de0e246c2c3cc63b362e00785657cafebeb1
Status: Downloaded newer image for ruby:2.7-alpine
docker.io/library/ruby:2.7-alpine

Note

If no tag is specified, it will default to latest tag.

2. Pulling image from private docker registry

To pull image from private docker registry like Gitlab registry, AWS ECR etc. full path of the image needs to be provided.

Usage

$ docker pull registry.example.com/mynamespace/myproject/my/image:rc1

Example

$ docker pull registry.gitlab.com/project/image:tag

Note

Authentication to private registry might be required prior to pulling the image.

3. Starting a container in daemon mode

Usage

$ docker run -dit --name container_name image:tag

Example

$ docker run -dit --name ruby_container ruby:2.7-alpine
e2ee5f8f33c7852d9660cb3b3b6fa11fd43deeb711b5fbb49040095d5641517e

Note

If no name is provided in the --name flag, then Docker will provde some random names to the container. It is recommended to provide a name so that the running containers can be identified easily.

4. Listing out containers

To list running container

Usage

$ docker ps

Example

$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
e2ee5f8f33c7        ruby:2.7-alpine     "irb"               3 seconds ago       Up 1 second                             ruby_container

To list all the containers including stopped ones

Usage

$ docker ps -a

The status of the container can be seen in the STATUS column in the result.

Example

$ docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS                     PORTS               NAMES
c3a599e12c9f        ruby:2.7-alpine     "ip a"              4 seconds ago        Exited (0) 3 seconds ago                       ruby_test
e2ee5f8f33c7        ruby:2.7-alpine     "irb"               About a minute ago   Up About a minute                              ruby_container

In this example we can see that the container ruby_test is not running and ruby_container is still running.

5. Stopping a running container

$ docker stop container_name

OR

$ docker stop container_id

6. Deleting a container

Only stopped containers can be deleted, so it is required to stop the container before deleting.

$ docker rm container_name

OR

$ docker rm container_id

Note

container_id can be obtained from the docker ps -a command.

Verify if the container has been deleted with

$ docker ps -a

7. Listing docker images

$ docker images

8. Removing docker images

$ docker rmi image_name:tag

OR

$ docker rmi image_id

Note

All the containers created from the image needs to be deleted before removing the image itself.
image_id can be obtained from the docker images command.

9. Passing Environment variables to Docker during runtime

Environment variables are passed with -e flag during creation of container from a Docker image.

docker run -dit --name project-x-backend -e BUCKET_NAME=x-bucket -e USERNAME=superadmin -e DB_URI=postgresql://admin:superDBpassword@db.server.net:5432/project-x-prod-db project-x:latest

Note

If multiple parameters are required to be passed in a docker run command such as multiple environment varialbes, ports etc. then it is recommended to use Docker Compose to manage all those with a single file.

Dockerfile References

1. Dockerfile Sample

FROM ruby:2.7-alpine

RUN apk update \
    && apk add --quiet gcc make

RUN gem update --system --quiet
RUN gem install bundler --quiet

WORKDIR /opt
COPY Gemfile Gemfile.lock /opt/
ENV BUNDLER_VERSION 2.0.1
RUN export BUNDLER_VERSION=2.0.1 && bundle install --quiet

COPY ./ /opt
RUN ln -sf /dev/stdout /opt/log/production.log

ENV ENVIRONMENT production

CMD sh -c "puma -e production"

2. Build Docker Image with Dockerfile

Usage

$ docker build -t registry.gitlab.com/project/image:tag .

OR

$ docker build -t registry.gitlab.com/project/image:tag -f /path/to/Dockerfile

3. Pushing Docker Image to Registry

Usage

docker push registry/scope/project/image:tag

Example

docker push registry.gitlab.com/project-x/backend:2.1

Contributors: Avash Mulmi ↩