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Before diving into Docker’s tricks, it’s vital to understand what Docker is and why it has become such a critical tool in the world of development and system administration. Docker is a container platform that allows developers and system administrators to efficiently and securely package, distribute, and manage applications. At the heart of Docker are containers, isolated environments where applications run, bypassing the issues of “it works on my machine”.
But now let’s get to what really matters, those Docker tricks that will make your life much easier.
Leveraging the Dockerfile
The Dockerfile is the document that defines how your Docker image, which will give life to your container, is built. You can see it as a recipe, where each line is an instruction to add ingredients (layers) to your image.
Don’t forget about .dockerignore: Just like with git, Docker has a system to ignore files. Any file or folder specified in .dockerignore will not be copied into the Docker image. This is useful for ignoring unnecessary files, like logs, node_modules files, or any others not needed to run your application.
Use of cache layers: Docker caches the image layers every time you build one. If you haven’t made changes to that specific layer, Docker will reuse it, speeding up the building process. If you place the instructions that change the least at the beginning of the Dockerfile, you’ll be able to take full advantage of this feature.
Playing with Containers
Containers are the essence of Docker, but they can also be tricky to handle if you don’t know some tricks.
Efficient container management: Docker offers several commands to manage containers. For example, you can use
docker ps -a to see all your containers (even the ones that are stopped),
docker stop $(docker ps -aq) to stop all running containers, and
docker rm $(docker ps -aq) to remove all containers.
Docker logs for debugging: If something goes wrong with your application, you can check your container logs with
docker logs CONTAINER_ID. You can even follow the logs in real-time with
docker logs -f CONTAINER_ID.
Docker Images: Less is More
Docker images can be huge if not handled correctly. Here are a few tricks to keep them as light as possible.
Use minimalist base images: There are many Docker base images available, but not all are created equal. Some are very heavy and contain a lot of things you probably don’t need. Try using minimalist base images like Alpine, which only have the essentials.
Remove cache after installations: When you install something with apt, yum, or any other package manager, it generates a cache that is not necessary to run your application. You can delete it on the same line where you install the package, so you don’t generate a new layer: for instance, you can use
RUN apt-get update && apt-get install -y my-package && rm -rf /var/lib/apt/lists/*.
Orchestrating Containers with Docker Compose
Docker Compose is an incredible tool that allows you to define and manage multiple containers at once. And, of course, it also has its own tricks.
Use environment variables: Docker Compose lets you define environment variables in a
.env file, which you can then use in your
docker-compose.yml file. This is very handy to avoid writing the same things over and over again.
Dependencies between containers: With Docker Compose, you can define dependencies between containers using the
depends_on option. This ensures that Docker Compose starts the containers in the correct order.
Creating Networks with Docker
Docker allows you to create networks to connect your containers so that they can communicate with each other.
Creating and managing networks: You can create a network with the
docker network create command. Once the network is created, you can connect a container to it with
docker network connect.
Inspecting networks: If you want to see what containers are connected to a network, you can use
docker network inspect.
Optimizing Docker Use
Finally, there are some general tricks that will help you make the most of Docker.
Docker system prune: Over time, you are likely to accumulate a bunch of images, containers, and networks that you no longer use. You can remove them all with
docker system prune.
Using Docker with CI/CD: Docker fits perfectly into any continuous integration and continuous deployment process. You can build your Docker image as part of your CI/CD pipeline, test it, and then deploy it to production.
I hope these tricks will help you master Docker and make your life a little easier. Remember, Docker is a powerful tool, but it can also be complicated. With these tips and tricks, you’ll be able to get the most out of Docker and avoid some of the most common issues.