Get PHP Composer to Run On Docker Container [A How To Guide]

I have a php docker container, that runs my app, and I need to start using Composer to install a php package. What is the best way to approach it?

Source files can be found here:

https://github.com/ikknd/docker-study in folder recipe-05

1. Not the best approach, but the most straightforward one: not to use "php:7.2-fpm" image, but to build a custom image with both php and composer.

Technically this works, I get composer installed in my php image, and whenever I need to update or install dependencies I simply execute calls in my custom php container.

Problems:

need to use composer in several different containers - results in custom images for each container, where composer is needed
if I run docker in swarm mode and scale container to more than 1 copy - results in each container executing "composer install"

2. A much better approach: use a dedicated composer docker image, map my project inside, and execute composer commands.

I will use ideas from recipe 02 - simple php page, and recipe 04 - redis setup.

Create docker-compose.yml file in "docker" folder:

Here I do several things:

/var/www/docker-study.loc/recipe-05/php:/app - composer image by default executes commands from /app folder, that's why I map project like this
I map /var/www/docker-study.loc/recipe-05/php to both, php container and composer container, this way composer container can execute "composer install", and php container will have the updated code
"depends_on" - prevents container to start before other container, on which it depends

3. Create composer.json in "php" folder:

4. Create index.php in "php" folder:

The goal here is to use composer library - "predis/predis" (just as an example). This library needs to get installed once "composer" container gets started.

I can go to /var/www/docker-study.loc/recipe-05/docker/ and execute:

docker-compose up -d

Now go to myapp.loc/ and see "works!"

5. Final Thoughts.

When composer container started, it executed "composer install" command and then exited. I can confirm this by running: "docker container ls -a" - this will show that container "docker_composer_1" has exited.

If I do - "docker logs docker_composer_1" - I can see information on what happened when container started, and how "composer install" process went.

What if I change composer.json file, and need to install additional library?

docker-compose restart composer

This will start this container again, execute install and exit.

What if I need to run "composer update" instead of "composer install"?

I can change "install" -> "update" in docker-compose.yml, and run "docker-compose restart composer"