How To Install and Use Docker Compose on Ubuntu 20.04

Publicada el por Stack Over Cloud

Introduction

Docker simplifies the process of managing application processes in containers. While containers are similar to virtual machines in certain ways, they are more lightweight and resource-friendly. This allows developers to break down an application environment into multiple isolated services.

For applications depending on several services, orchestrating all the containers to start up, communicate, and shut down together can quickly become unwieldy. Docker Compose is a tool that allows you to run multi-container application environments based on definitions set in a YAML file. It uses service definitions to build fully customizable environments with multiple containers that can share networks and data volumes.

In this guide, we’ll demonstrate how to install Docker Compose on an Ubuntu 20.04 server and how to get started using this tool.

Prerequisites

To follow this article, you will need:

Step 1 — Installing Docker Compose

To make sure we obtain the most updated stable version of Docker Compose, we’ll download this software from its official Github repository.

First, confirm the latest version available in their releases page. At the time of this writing, the most current stable version is 1.26.0.

The following command will download the 1.26.0 release and save the executable file at /usr/local/bin/docker-compose, which will make this software globally accessible as docker-compose:

  • sudo curl -L "https://github.com/docker/compose/releases/download/1.26.0/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

Next, set the correct permissions so that the docker-compose command is executable:

  • sudo chmod +x /usr/local/bin/docker-compose

To verify that the installation was successful, you can run:

  • docker-compose --version

You’ll see output similar to this:

Output
docker-compose version 1.26.0, build 8a1c60f6

Docker Compose is now successfully installed on your system. In the next section, we’ll see how to set up a docker-compose.yml file and get a containerized environment up and running with this tool.

Step 2 — Setting Up a docker-compose.yml File

To demonstrate how to set up a docker-compose.yml file and work with Docker Compose, we’ll create a web server environment using the official Nginx image from Docker Hub, the public Docker registry. This containerized environment will serve a single static HTML file.

Start off by creating a new directory in your home folder, and then moving into it:

  • mkdir ~/compose-demo

  • cd ~/compose-demo

In this directory, set up an application folder to serve as the document root for your Nginx environment:

  • mkdir app

Using your preferred text editor, create a new index.html file within the app folder:

  • nano app/index.html

Place the following content into this file:

~/compose-demo/app/index.html
<!doctype html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title>Docker Compose Demo</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/gh/kognise/water.css@latest/dist/dark.min.css">
</head>
<body>

    <h1>This is a Docker Compose Demo Page.</h1>
    <p>This content is being served by an Nginx container.</p>

</body>
</html>

Save and close the file when you’re done. If you are using nano, you can do that by typing CTRL+X, then Y and ENTER to confirm.

Next, create the docker-compose.yml file:

  • nano docker-compose.yml

Insert the following content on your docker-compose.yml file:

docker-compose.yml
version: '2.0'
services:
  web:
    image: nginx:alpine
    ports:
      - "8000:80"
    volumes:
      - ./app:/usr/share/nginx/html

The docker-compose.yml file typically starts off with the version definition. This will tell Docker Compose which configuration version we’re using.

We then have the services block, where we set up the services that are part of this environment. In our case, we have a single service called web. This service uses the nginx:alpine image and sets up a port redirection with the ports directive. All requests on port 8000 of the host machine (the system from where you’re running Docker Compose) will be redirected to the web container on port 80, where Nginx will be running.

The volumes directive will create a shared volume between the host machine and the container. This will share the local app folder with the container, and the volume will be located at /usr/share/nginx/html inside the container, which will then overwrite the default document root for Nginx.

Save and close the file.

We have set up a demo page and a docker-compose.yml file to create a containerized web server environment that will serve it. In the next step, we’ll bring this environment up with Docker Compose.

Step 3 — Running Docker Compose

With the docker-compose.yml file in place, we can now execute Docker Compose to bring our environment up. The following command will download the necessary Docker images, create a container for the web service, and run the containerized environment in background mode:

  • docker-compose up -d

Docker Compose will first look for the defined image on your local system, and if it can’t locate the image it will download the image from Docker Hub. You’ll see output like this:

Output
Creating network "compose-demo_default" with the default driver
Pulling web (nginx:alpine)...
alpine: Pulling from library/nginx
cbdbe7a5bc2a: Pull complete
10c113fb0c77: Pull complete
9ba64393807b: Pull complete
c829a9c40ab2: Pull complete
61d685417b2f: Pull complete
Digest: sha256:57254039c6313fe8c53f1acbf15657ec9616a813397b74b063e32443427c5502
Status: Downloaded newer image for nginx:alpine
Creating compose-demo_web_1 ... done

Your environment is now up and running in the background. To verify that the container is active, you can run:

  • docker-compose ps

This command will show you information about the running containers and their state, as well as any port redirections currently in place:

Output
       Name                     Command               State          Ports        
----------------------------------------------------------------------------------
compose-demo_web_1   /docker-entrypoint.sh ngin ...   Up      0.0.0.0:8000->80/tcp

You can now access the demo application by pointing your browser to either localhost:8000 if you are running this demo on your local machine, or your_server_domain_or_IP:8000 if you are running this demo on a remote server.

Note: if you are running this demo on a remote server that has the UFW firewall enabled, you’ll have to allow access on port 8000 in order to be able to access the demo from a browser running on your local machine:

  • sudo ufw allow in 8000

You’ll see a page like this:

Docker Compose Demo Page

Because the shared volume you’ve set up within the docker-compose.yml file keeps your app folder files in sync with the container’s document root. If you make any changes to the index.html file, they will be automatically picked up by the container and thus reflected on your browser when you reload the page.

In the next step, you’ll see how to manage your containerized environment with Docker Compose commands.

Step 4 — Getting Familiar with Docker Compose Commands

You’ve seen how to set up a docker-compose.yml file and bring your environment up with docker-compose up. You’ll now see how to use Docker Compose commands to manage and interact with your containerized environment.

To check the logs produced by your Nginx container, you can use the logs command:

  • docker-compose logs

You’ll see output similar to this:

Output
Attaching to compose-demo_web_1
web_1  | /docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
web_1  | /docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
web_1  | /docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
web_1  | 10-listen-on-ipv6-by-default.sh: Getting the checksum of /etc/nginx/conf.d/default.conf
web_1  | 10-listen-on-ipv6-by-default.sh: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf
web_1  | /docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
web_1  | /docker-entrypoint.sh: Configuration complete; ready for start up
web_1  | 172.22.0.1 - - [02/Jun/2020:10:47:13 +0000] "GET / HTTP/1.1" 200 353 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.61 Safari/537.36" "-"

If you want to pause the environment execution without changing the current state of your containers, you can use:

  • docker-compose pause

Output
Pausing compose-demo_web_1 ... done

To resume execution after issuing a pause:

  • docker-compose unpause

Output
Unpausing compose-demo_web_1 ... done

The stop command will terminate the container execution, but it won’t destroy any data associated with your containers:

  • docker-compose stop

Output
Stopping compose-demo_web_1 ... done

If you want to remove the containers, networks, and volumes associated with this containerized environment, use the down command:

  • docker-compose down

Output
Removing compose-demo_web_1 ... done
Removing network compose-demo_default

Notice that this won’t remove the base image used by Docker Compose to spin up your environment (in our case, nginx:alpine). This way, whenever you bring your environment up again with a docker-compose up, the process will be much faster since the image is already on your system.

In case you want to also remove the base image from your system, you can use:

  • docker image rm nginx:alpine

Output
Untagged: nginx:alpine
Untagged: nginx@sha256:b89a6ccbda39576ad23fd079978c967cecc6b170db6e7ff8a769bf2259a71912
Deleted: sha256:7d0cdcc60a96a5124763fddf5d534d058ad7d0d8d4c3b8be2aefedf4267d0270
Deleted: sha256:05a0eaca15d731e0029a7604ef54f0dda3b736d4e987e6ac87b91ac7aac03ab1
Deleted: sha256:c6bbc4bdac396583641cb44cd35126b2c195be8fe1ac5e6c577c14752bbe9157
Deleted: sha256:35789b1e1a362b0da8392ca7d5759ef08b9a6b7141cc1521570f984dc7905eb6
Deleted: sha256:a3efaa65ec344c882fe5d543a392a54c4ceacd1efd91662d06964211b1be4c08
Deleted: sha256:3e207b409db364b595ba862cdc12be96dcdad8e36c59a03b7b3b61c946a5741a

Note: Please refer to our guide on How to Install and Use Docker for a more detailed reference on Docker commands.

Conclusion

In this guide, we’ve seen how to install Docker Compose and set up a containerized environment based on an Nginx web server image. We’ve also seen how to manage this environment using Compose commands.

For a complete reference of all available docker-compose commands, check the official documentation.

Originally posted on DigitalOcean Community Tutorials
Author: Erika Heidi

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