Posted on by cipherify

Docker – compose

Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration.

Using Compose is basically a three-step process:

  1. Define your app’s environment with a Dockerfile so it can be reproduced anywhere.
  2. Define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.
  3. Run docker-compose up and Compose starts and runs your entire app.

Install Compose on Linux systems

On Linux, you can download the Docker Compose binary from the Compose repository release page on GitHub. Follow the instructions from the link, which involve running the curl command in your terminal to download the binaries. These step-by-step instructions are also included below.

For alpine, the following dependency packages are needed: py-pip, python-dev, libffi-dev, openssl-dev, gcc, libc-dev, and make.

  1. Run this command to download the current stable release of Docker Compose:
sudo curl -L "https://github.com/docker/compose/releases/download/1.27.4/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

To install a different version of Compose, substitute 1.27.4 with the version of Compose you want to use.

  • Apply executable permissions to the binary:
sudo chmod +x /usr/local/bin/docker-compose

Note: If the command docker-compose fails after installation, check your path. You can also create a symbolic link to /usr/bin or any other directory in your path.

For example:

sudo ln -s /usr/local/bin/docker-compose /usr/bin/docker-compose
  1. Optionally, install command completion for the bash and zsh shell.
  2. Test the installation.
$ docker-compose --version
docker-compose version 1.27.4, build 1110ad01

Uninstallation

To uninstall Docker Compose if you installed using curl:

$ sudo rm /usr/local/bin/docker-compose

To uninstall Docker Compose if you installed using pip:

$ pip uninstall docker-compose

How to Deploy Application using Docker-Compose

Step: 1

Create application folder and place the code in that Folder.

Step: 2

Create Dockerfile to create Docker Image for mentioned Source code in Step 1.

e.g.:

Dockerfile

FROM python:3.7-alpine

WORKDIR /app

ENV FLASK_APP=app.py

ENV FLASK_RUN_HOST=127.0.0.1

COPY requirements.txt requirements.txt

RUN pip3 install -r requirements.txt

EXPOSE 5000

COPY . .

CMD [“flask”, “run”]

Step 3: Define services in a Compose file

Create a file called docker-compose.yml in your project directory and paste the following:

version: "3.8"
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: "redis:alpine"

This Compose file defines two services: web and redis.

Web service

The web service uses an image that’s built from the Dockerfile in the current directory. It then binds the container and the host machine to the exposed port, 5000. This example service uses the default port for the Flask web server, 5000.

Redis service

The redis service uses a public Redis image pulled from the Docker Hub registry.

From your project directory, start up your application by running docker-compose up.

$ docker-compose up

Creating network “composetest_default” with the default driver

Creating composetest_web_1 …

Creating composetest_redis_1 …

Creating composetest_web_1

Creating composetest_redis_1 … done

Attaching to composetest_web_1, composetest_redis_1

web_1    |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

redis_1  | 1:C 17 Aug 22:11:10.480 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo

redis_1  | 1:C 17 Aug 22:11:10.480 # Redis version=4.0.1, bits=64, commit=00000000, modified=0, pid=1, just started

redis_1  | 1:C 17 Aug 22:11:10.480 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf

web_1    |  * Restarting with stat

redis_1  | 1:M 17 Aug 22:11:10.483 * Running mode=standalone, port=6379.

web_1    |  * Debugger is active!

redis_1  | 1:M 17 Aug 22:11:10.483 # Server initialized

web_1    |  * Debugger PIN: 330-787-903

redis_1  | 1:M 17 Aug 22:11:10.483 * Ready to accept connections

Compose pulls a Redis image, builds an image for your code, and starts the services you defined. In this case, the code is statically copied into the image at build time.

  • Enter http://localhost:5000/ in a browser to see the application running.

If you’re using Docker natively on Linux, Docker Desktop for Mac, or Docker Desktop for Windows, then the web app should now be listening on port 5000 on your Docker daemon host. Point your web browser to http://localhost:5000 to find the Hello World message. If this doesn’t resolve, you can also try http://127.0.0.1:5000.

If you want to run your services in the background, you can pass the -d flag (for “detached” mode) to docker-compose up and use docker-compose ps to see what is currently running:

$ docker-compose up -d
Starting composetest_redis_1...
Starting composetest_web_1...
$ docker-compose ps
Name                 Command            State       Ports
composetest_redis_1   /usr/local/bin/run         Up
composetest_web_1     /bin/sh -c python app.py   Up      5000->5000/tcp

The docker-compose run command allows you to run one-off commands for your services. For example, to see what environment variables are available to the web service:

$ docker-compose run web env

See docker-compose --help to see other available commands. You can also install command completion for the bash and zsh shell, which also shows you available commands.

If you started Compose with docker-compose up -d, stop your services once you’ve finished with them:

$ docker-compose stop

You can bring everything down, removing the containers entirely, with the down command. Pass --volumes to also remove the data volume used by the Redis container:

$ docker-compose down --volumes

Control startup and shutdown order in Compose

You can control the order of service startup and shutdown with the depends on option. Compose always starts and stops containers in dependency order, where dependencies are determined by depends_on, links, volumes_from, and network_mode: "service:...".

However, for startup Compose does not wait until a container is “ready” 

For example, to use wait-for-it.sh or wait-for to wrap your service’s command:

version: “2”

services:

  web:

    build: .

    ports:

      – “80:8000”

    depends_on:

      – “db”

    command: [“./wait-for-it.sh”, “db:5432”, “–“, “python”, “app.py”]

  db:

    image: postgres

Above compose file create web service post db service creation.

References:

  1. https://docs.docker.com
  2. from Miscellaneous technical websites.