Hands-On Docker Compose Guide

In a world where it is not uncommon for companies to have millions of containers, simply managing them through the docker CLI will not suffice. We need a tool that can help us manage chunks of containers and define them in a human-readable format. That is exactly what docker compose does.

Basics

At the most basic level, docker compose uses code to manage your infrastructure. This code is written in yaml format. The file that the code is written in is called docker-compose.yaml. Here is a basic docker-compose.yaml file:

version: '3.8'

services:
  service1:
    image: nginx:alpine
    ports:
      - "80:80"
  service2:
    image: alpine

networks:
  mynetwork:

As you can see, the structure of the file is quite basic. Let's go through everything 1 by 1.

  • version: This specifies the version of docker compose in use by the file.
  • services: This specifies the services that the file defines. Each service is, essentially, just the definition for a container. When the file is deployed, 1 container is made out of each service.
    • <service_name>: A single docker-compose.yaml file can have several services. Each service has it's own name. This is how you define the name.
      • image: This is the image that will be used for the container that will be created when this is deployed. Does the same thing as
      • ports: This works the same way as the ports option in the docker run command.
    • ...: There can be many services
  • networks: This is the definition for docker networks.

As you can see, most things work the same way in docker compose as they do in docker. They are just written in yaml format.

Hands-On exercises

Docker compose is a very unique concept. Most things can be explained through theory. Practical experience just reinforces that theory. Docker compose, on the other hand, is very simple to understand the basics of. While I can explain the more complicated concepts through theory, it will be the most dry, dull, and boring thing you have ever heard. This is why I will teach you through making you do hands-on exercises.

In these hands-on exercises, you will need to write docker-compose.yaml files on your own. For your reference, I will give you the docker compose documentation. I will provide you with the solution, but I encourage you to try on your own first.

Basic Web Server

We are going to start with something very simple. You have an HTML file. You need to host a web server on docker with it.

<!DOCTYPE html>
<html>
<head>
    <title>The best website ever!</title>
</head>
<body>
    <h1>Welcome to the website!</h1>
</body>
</html>

Make sure you follow best practices. Since you do not expect this data to change and this is quite a small file, you should not use volumes. Instead, you should create an image the file in it.

Also make sure you do not build the image in advance. You need to make it so the image is built on deployment.

After you come up with a solutions, do not check it immediately. Test it with the following command. Before you run this, make sure you have docker compose installed. Here is a guide.

docker-compose up -d --force-recreate

After you make changes, execute the same command and the updates will be carried out automatically.

If there is something wrong, try to figure it out. Looking at my answer should only be done once you have tried everything.

Solution

There are several solutions, but this is what I used.

docker-compose.yaml:

version: '3.8'
services:
 service1:
  build: .
  ports:
  - "80:80"

Dockerfile:

FROM httpd
COPY ./index.html /usr/local/apache2/htdocs/

This assumes that all these files are in a single directory, and the HTML file is named index.html. You can adapt this to your specific case.

If you got this right first try, you are doing great! You will be a docker compose wizard in no time.

If you struggled on this, that if fine. It's expected. You will only get better with practice.

Multi-Container App

The previous exercise was great to get your feet wet with docker compose, but that wasn't really something useful. All you did is deploy a web server on a container. Now, it's time to take it up a notch. You will be using containers for what they are best for, modularized application components. In short, microservices.

zip.zip

This zip file has all the files you will need to do this. This time, I have given you all the dockerfiles so you do not have the hassle of writing that.

Here are some requirements for this. Because of how important network isolation is, you need to make sure you create a seperate network specifically for this. No ports should be exposed except for the ones that are required. Also make sure that the name of the API container is api. Don't just name the service api. That will not work.

Solution

Here is the docker compose file that works. There are other ways to do it.:

version: '3.8'

services:
 api:
 build:
 context: .
 dockerfile: dockerfile_api
 container_name: api
 networks:
 - app

 web:
 build:
 context: .
 dockerfile: dockerfile_web
 ports:
 - "80:80"
 networks:
 - app

networks:
 app:

Conclusion

Docker compose is a very complicated subject. I haven't even scratched the surface. This was my attempt to teach you docker compose in the most fun way possible. If you have another topic to discuss, you think I could have done something better, or you just want to ask me a question, just drop a comment. I will try my best to help. Before you leave, here is something that will help you.

reference.md

Not only does it have all the things that we covered here, I also added a couple things I thought you might find useful when using docker compose in the real world. Thank you for reading.

Comments

Post a Comment

Popular posts from this blog

Persistent Data in Docker: Explanation + Hands-On Demo

Docker containers, by nature, are ephemeral. They are not designed to stay without being deleted for long periods of time. While you could, theoretically never delete the image, most of the benefits of docker are realized when containers are temporary. There is something wrong with this approach, though. Almost all the data in the world is designed to be persistent. This poses a problem that docker volumes can solve. What are docker volumes? Docker volumes are a method of ensuring data persistence in a containerized environment. To comply with best practices, you need to make sure that spontaneously losing a container or 2 does not have an impact on anything but the performance of your infrastructure. To do this, all the important data in your containers needs to be put somewhere. Somewhere which is not liked to the life-cycle of the container itself. That somewhere is a volume. A docker volume is little more than a place to store data. From the point of view of the container, nothing
Read more

Pods to Deployments | Kubernetes Architecture Evolution

Image
When I was learning the basic kubernetes concepts, I was confused between pods, replicasets, and deployments. Each one seemed to have the other inside of it. I remained confused for a long time. I kept trying to avoid the topic. When I actually understood, it felt great. I do not want you to have that confusion when you are learning these concepts. That is why I created this post. Manifest files As we talked about in our previous post, to access your cluster, you use a tool called kubectl . While you can execute commands to deploy and manage resources, there is a better way of doing it. As you must know if you have read my posts about docker compose , Infrastructure As Code is often more efficient and easier to manage when compared to traditional CLI tools. This is why kubernetes also supports infrastructure as code. It is written in yaml. Those files are called kubernetes manifest files. It is best practice to use them. That is why we are going to be using them here. Step 1: Deploying
Read more

Docker Compose Explained: Simplifying Multi-Container Deployments

Docker compose and other IaC (Infrastructure as Code) tools are very important to learn. Today, they are almost essential knowledge to manage any sort of infrastructure, anywhere. Docker Compose is one of the most prominent tools in this space. According to Stackshare, at the time of writing, there are about 2108 companies using docker compose in their tech stack. This includes giant companies like Udemy. The knowledge of this relatively simple tool is very important. That is why I am going to break it down for you here. What is Docker Compose As mentioned before, Docker Compose is an IaC tool for Docker containers. It makes it significantly easier to deploy and manage containers in an environment with several containers. Why Docker Compose Now that you know what docker compose is, let's talk about why somebody would need such a tool. What benefits does it provide? Simplifies Deployment: Docker compose simplifies deployment. Once you have the IaC template in place, you can deploy a
Read more