A Deep Dive into Docker

The advent of Docker has revolutionized the way we run, deploy, and maintain our applications. With the rise of containerization, we’ve been able to abstract away much of the underlying infrastructure and dependencies that applications rely on, making it easier than ever to deploy and manage them across different environments. However, with great power comes great responsibility, and we must understand the internals of Docker and establish good practices to ensure that our applications are secure, reliable, and performant.

In this chapter, we’ll delve into the nitty-gritty of Docker, exploring its architecture, components, and key features. We’ll also examine some of the helper projects that have emerged on top of Docker, such as Docker Compose and Kubernetes, and learn how to use them to build more complex and scalable applications. Throughout, we’ll emphasize best practices for working with Docker, such as creating efficient...

Docker advanced use cases

While using Docker and its CLI, there are a lot of things we will need to take care of in terms of the life cycle of the container, build process, volumes, and networking. Some of those things you can automate by using other tools, but it’s still useful to know what’s going on underneath.

Running public images

A lot of public images you can find on Docker Hub (https://hub.docker.com) have initialization scripts available that take configuration from environment variables or the mounted files to a predefined directory.

The most commonly used image that uses both techniques is images with databases. Let’s look for an official Docker PostgreSQL image. You can find the one we’ll be using here: https://hub.docker.com/_/postgres.

To run the official PostgreSQL Docker image, you can use the following command:

admin@myhome:~$ docker run --name some-postgres -e POSTGRES_PASSWORD=mysecretpassword -d postgres

In this command...

Docker Compose

Docker Compose is a console tool for running multiple containers using one command. It provides an easy way to manage and coordinate multiple containers, making it easier to build, test, and deploy complex applications. With Docker Compose, you can define your application’s services, networks, and volumes in a single YAML file, and then start and stop all services from the command line.

To use Docker Compose, you first need to define your application’s services in a docker-compose.yml file. This file should include information about the services you want to run, their configuration, and how they are connected. The file should also specify which Docker images to use for each service.

The docker-compose.yaml file is a central configuration file that’s used by Docker Compose to manage the deployment and running of applications. It is written in YAML syntax.

The structure of the docker-compose.yaml file is divided into several sections, each...

Advanced Dockerfile techniques

Dockerfiles are used to define how an application should be built inside a Docker container. We covered most of the available commands in Chapter 8. Here, we will introduce more advanced techniques, such as multi-stage builds or not-so-common ADD command uses.

Multi-stage build

Multi-stage builds are a feature of Docker that allows you to use multiple Docker images to create a single final image. By creating multiple stages, you can separate the build process into distinct steps and reduce the size of the final image. Multi-stage builds are particularly useful when building complex applications that require multiple dependencies as they allow developers to keep the necessary dependencies in one stage and the application in another.

One example of using multi-stage builds with a Golang application involves creating two stages: one for building the application and one for running it. In the first stage, the Dockerfile pulls in the necessary dependencies...

Docker orchestration

In the world of containerization, orchestration is the process of automating deployment and managing and scaling your applications across multiple hosts. Orchestration solutions help simplify the management of containerized applications, increase availability, and improve scalability by providing a layer of abstraction that allows you to manage containers at a higher level, instead of manually managing individual containers.

Docker Swarm is a Docker-native clustering and orchestration tool that allows you to create and manage a cluster of Docker nodes, allowing users to deploy and manage Docker containers across a large number of hosts. Docker Swarm is an easy-to-use solution that comes built-in with Docker, making it a popular choice for those who are already familiar with Docker.

Kubernetes is an open source container orchestration platform that was originally developed by Google. Kubernetes allows you to deploy, scale, and manage containerized applications...

Summary

In this chapter, we covered more advanced topics around Docker, only touching topics around orchestration. Kubernetes, OpenShift, and SaaS solutions provided by cloud operators are driving the creation of new tools that will further ease Docker’s use in modern applications.

Docker has had a profound impact on the world of software development and deployment, enabling us to build, ship, and run applications more efficiently and reliably than ever before. By understanding the internals of Docker and following best practices for working with it, we can ensure that our applications are secure, performant, and scalable across a wide range of environments.

In the next chapter, we will look into challenges on how to monitor and gather logs in a distributed environment built on top of Docker containers.