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docker-compose & Exposed Ports


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We need to get a database running: MySQL, Postgresql, whatever. If you already have one running, awesome! All you need to do is copy your DATABASE_URL environment variable, open or create a .env.local file, paste, then change it to match whatever your local setup is using. If you decide to do this, feel free to skip ahead to the end of chapter 4 where we configure the server_version.

Docker Just for the Database

For me, I do not have a database running locally on my system... and I'm not going to install one. Instead, I want to use Docker. And, we're going to use Docker in an interesting way. I do have PHP installed locally:

php -v

So I won't use Docker to create a container specifically for PHP. Instead I'm going to use Docker simply to help boot up any services my app needs locally. And right now, I need a database service. Thanks to some magic between Docker and the Symfony binary, this is going to be super easy.

To start, remember when the Doctrine recipe asked us if we wanted Docker configuration? Because we said yes, the recipe gave us docker-compose.yml and docker-compose.override.yml files. When Docker boots, it will read both of these... and they're split into two pieces just in case you want to also use Docker to deploy to production. But we're not going to worry about that: we just want to use Docker to make life easier for local development.

22 lines | docker-compose.yml
version: '3'
###> doctrine/doctrine-bundle ###
image: postgres:${POSTGRES_VERSION:-13}-alpine
# You should definitely change the password in production
- db-data:/var/lib/postgresql/data:rw
// ... lines 14 - 22

9 lines | docker-compose.override.yml
version: '3'
###> doctrine/doctrine-bundle ###
- "5432"
// ... lines 8 - 9

These files say that they will boot a single Postgres database container with a user called symfony and password ChangeMe:


The username changed from symfony to app in the newest recipe version.

It will also expose port 5432 of the container - that's Postgres's normal port - to our host machine on a random port. This means that we're going to be able to talk to the Postgresql Docker container as if it were running on our local machine... as long as we know the random port that Docker chose. We'll see how that works in a minute.

By the way, if you want to use MySQL instead of Postgres, you absolutely can. Feel free to update these files... or delete both of them and run:

php bin/console make:docker:database

to generate a new compose file for MySQL or MariaDB. I'm going to stick with Postgres because it's awesome.

At this point, we're going to start Docker and learn a bit about how to communicate with the database that lives inside. If you're pretty comfortable with Docker, feel free to skip to the next chapter.

Starting the Container

Anyways, let's get our container running. First, make sure you have Docker actually installed on your machine: I won't show that because it varies by operating system. Then, find your terminal and run:

docker-compose up -d

The -d means "run in the background as a daemon". The first time you run this, it'll probably download a bunch of stuff. But eventually, our container should start!

Communicating with the Container

Cool! But now what? How can we talk to the container? Run a command called:

docker-compose ps

This shows info about all the containers currently running... just one for us. The really important thing is that port 5432 in the container is connected to port 50700 on my host machine. This means that if we talk to this port, we will actually be talking to that Postgres database. Oh, and this port is random: it'll be different on your machine... and it'll even change each time we stop and start our container. More on that soon.

But now that we know about port 50700, we can use that to connect to the database. For example, because I'm using Postgres, I could run:

psql --user=symfony --port=50700 --host= --password app

That means: connect to Postgres at port 50700 using user symfony and talking to the app database. All of this is configured in the docker-compose.yml file. Copy the ChangeMe password because that last flag tells Postgres to ask for that password. Paste and... we're in!

If you're using MySQL, we can do this same thing with a mysql command.

But, this only works if we have that psql command installed on our local machine. So let's try a different command. Run:

docker-compose ps

again. The container is called database, which comes from our docker-compose.yml file. So we can change the previous command to:

docker-compose exec database psql --username symfony --password app

This time, we're executing the psql command inside the container, so we don't need to install it locally. Type ChangeMe for the password and... we're back in!

The point is: just by running docker-compose up, we have a Postgres database container that we can talk to!

Stopping the Container

Btw, when you're ready to stop the container later, you can run:

docker-compose stop

That basically turns the container off. Or you can run the more common:

docker-compose down

which turns off the containers and removes them. To start back up, it's the same:

docker-compose up -d

But notice that when we run docker-compose ps again, the port on my host machine is a different random port! So, in theory, we could configure the DATABASE_URL variable to point to our Postgres database, including using the correct port. But that random port that keeps changing is going to be annoying!

Fortunately, there's a trick for this! It turns our, our app is already configured, without us doing anything! That's next.