At the moment, this Docker guide focuses on tips that can help while working on the Code Self Study website. To learn the basics of Docker, it might be a good idea to start with the official Docker guides.
A Docker container is something like a virtual computer that runs inside of your computer. Instead of installing software (like a database) on your computer directly, you can put it in its own container and run it from there. Multiple containers can be networked with each other to communicate. An end result of using Docker is that all the programmers on a project have the same development environment, including the same versions of all the required software.
A Docker image is a kind of blueprint for a container.
Docker containers are created from the images. You can have multiple docker containers that are based on the same image.
A Docker network connects multiple containers. If you use Docker Compose to manage your containers, it will automatically create the network for you.
A Docker volume mounts files and persists data after a Docker container is destroyed.
The base Docker command is
docker. Other parts of Docker have sub-commands. For example, the commands for managing containers are behind
docker container, the commands for managing images are behind
docker image, and the commands for managing volumes are behind
To list your Docker images, you would use:
$ docker image ls
To list your Docker containers, you would use:
$ docker container ps
The built-in help is good -- just type
docker container to see the options for that sub-command.
You can download pre-made Docker images with the
docker pull command, but the Code Self Study website creates custom images by using Docker Compose and Dockerfiles. If you look inside the
Dockerfile.dev files in the project, you can see the commands that are run.
For example, the
Dockerfile.dev file for the Express.js server looks something like this:
FROM node:12-alpine WORKDIR /app COPY package*.json ./ RUN npm install COPY . . EXPOSE 5000 CMD ["npm", "start"]
- Start with a preexisting Node.js image from Docker Hub (like Github for Docker images), using Node version 12 and Alpine Linux (a very small Linux distro).
- Set the working directory inside the images to
- Copy the
package.jsonfile(s) to the working directory.
- Install the dependencies.
- Copy the Express.js code into the working directory.
- Suggest exposing port 5000 for the Express server.
- Start the Express server with
Dockerfile can be built manually, but in the case of Code Self Study, all the containers are built with the
docker-compose.yml file. Take a look in that file to see how the
Dockerfiles are used.
# The API for the puzzle server express_api: # wait for other containers to start first depends_on: - mongo - redis # build from the ./containers/express_api/Dockerfile.dev file build: dockerfile: Dockerfile.dev context: ./containers/express_api # mount the project files inside the container volumes: - /app/node_modules - ./containers/express_api:/app # set some environment variables environment: - REDIS_HOST=redis - REDIS_PORT=6379 - SESSION_SECRET="this is only for development"
Rebuilding the entire application can take a while, and sometimes you will just want to restart one container (like the Gatsby container).
Here's how to restart a Docker container.
First, get a list of running containers:
$ docker container ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES f9466971430a codeselfstudy_nginx "nginx -g 'daemon of…" 6 minutes ago Up 6 minutes 0.0.0.0:4444->80/tcp codeselfstudy_nginx_1 b9b10f71037f codeselfstudy_gatsby "docker-entrypoint.s…" 6 minutes ago Up 6 minutes codeselfstudy_gatsby_1 18febd3d8b84 codeselfstudy_express_api "docker-entrypoint.s…" 6 minutes ago Up 6 minutes 5000/tcp codeselfstudy_express_api_1 d2d54e20f529 mongo "docker-entrypoint.s…" 6 minutes ago Up 6 minutes 27017/tcp codeselfstudy_mongo_1 75df2bbce79f redis:latest "docker-entrypoint.s…" 6 minutes ago Up 6 minutes 6379/tcp codeselfstudy_redis_1
If the container that you want to restart is
codeselfstudy_gatsby_1, then copy the container ID and restart it like this:
$ docker container restart b9b10f71037f
You can also refer to it by the full name, if that's easier:
$ docker container restart codeselfstudy_gatsby_1
After a while, it's possible that Docker images will take up a lot of hard drive space. It's easy to clean them.
To list the images use this command:
$ docker image ls REPOSITORY TAG IMAGE ID CREATED SIZE <none> <none> 7d3aa3d696c0 2 minutes ago 307MB codeselfstudy_express_api latest c7a0d49e0ade 2 minutes ago 140MB
To remove an image, for example the unnamed image above, refer to it by the
$ docker image rm 7d3aa3d696c0
You can list the dangling images (untagged as
<none>) with this command:
$ docker image ls -f "dangling=true" -q
And delete them with this command:
$ docker image rm $(docker image ls -f "dangling=true" -q)
Or just use this command to remove the dangling images, stopped containers, and reclaim other space:
$ docker system prune
To see how much space Docker is using type this:
$ docker system df TYPE TOTAL ACTIVE SIZE RECLAIMABLE Images 28 5 14.27GB 13.53GB (94%) Containers 5 5 263B 0B (0%) Local Volumes 58 5 784.7MB 428.7MB (54%) Build Cache 0 0 0B 0B
Here are some quick tips for common tasks.
Get the ID of the stopped container:
docker container ps -a
docker container commit <container_id> tmp_container
tmp_container is arbitrary. Name it whatever you want.
Then run it like this:
docker container run -it --entrypoint=sh tmp_container
More info is here.
Here are some examples of how to run commands inside of containers by name when using
# start up the docker containers docker-compose -f docker-compose.dev.yml up --build # run commands inside of containers docker-compose -f docker-compose.dev.yml exec django python manage.py makemigrations docker-compose -f docker-compose.dev.yml exec django python manage.py migrate docker-compose -f docker-compose.dev.yml exec django python manage.py createsuperuser # restart containers docker-compose -f docker-compose.dev.yml exec django restart # load seed data docker-compose -f docker-compose.dev.yml exec django python manage.py loaddata apps/app_name/fixtures/my_data.fixtures.json docker-compose -f docker-compose.dev.yml exec django python manage.py loaddata apps/app_name/fixtures/other_data.yaml # shut down docker containers docker-compose -f docker-compose.dev.yml down