334 lines
11 KiB
Markdown
334 lines
11 KiB
Markdown
|
|
[Docker Compose](https://docs.docker.com/compose/) is a tool that was developed to help define and
|
|
share multi-container applications. With Compose, we can create a YAML file to define the services
|
|
and with a single command, can spin everything up or tear it all down.
|
|
|
|
The _big_ advantage of using Compose is you can define your application stack in a file, keep it at the root of
|
|
your project repo (it's now version controlled), and easily enable someone else to contribute to your project.
|
|
Someone would only need to clone your repo and start the compose app. In fact, you might see quite a few projects
|
|
on GitHub/GitLab doing exactly this now.
|
|
|
|
So, how do we get started?
|
|
|
|
## Installing Docker Compose
|
|
|
|
Since you installed Docker Desktop/Toolbox for either Windows or Mac, you already have Docker Compose!
|
|
Play-with-Docker instances already have Docker Compose installed as well. If you are on
|
|
a Linux machine, you will need to install Docker Compose using
|
|
[the instructions here](https://docs.docker.com/compose/install/).
|
|
|
|
After installation, you should be able to run the following and see version information.
|
|
|
|
```bash
|
|
docker-compose version
|
|
```
|
|
|
|
|
|
## Creating our Compose File
|
|
|
|
1. At the root of the app project, create a file named `docker-compose.yml`.
|
|
|
|
1. In the compose file, we'll start off by defining the schema version. In most cases, it's best to use
|
|
the latest supported version. You can look at the [Compose file reference](https://docs.docker.com/compose/compose-file/)
|
|
for the current schema versions and the compatibility matrix.
|
|
|
|
```yaml
|
|
version: "3.7"
|
|
```
|
|
|
|
1. Next, we'll define the list of services (or containers) we want to run as part of our application.
|
|
|
|
```yaml hl_lines="3"
|
|
version: "3.7"
|
|
|
|
services:
|
|
```
|
|
|
|
And now, we'll start migrating a service at a time into the compose file.
|
|
|
|
|
|
## Defining the App Service
|
|
|
|
To remember, this was the command we were using to define our app container.
|
|
|
|
```bash
|
|
docker run -dp 3000:3000 \
|
|
-w /app -v $PWD:/app \
|
|
--network todo-app \
|
|
-e MYSQL_HOST=mysql \
|
|
-e MYSQL_USER=root \
|
|
-e MYSQL_PASSWORD=secret \
|
|
-e MYSQL_DB=todos \
|
|
node:12-alpine \
|
|
sh -c "yarn install && yarn run dev"
|
|
```
|
|
|
|
1. First, let's define the service entry and the image for the container. We can pick any name for the service.
|
|
The name will automatically become a network alias, which will be useful when defining our MySQL service.
|
|
|
|
```yaml hl_lines="4 5"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
image: node:12-alpine
|
|
```
|
|
|
|
1. Typically, you will see the command close to the `image` definition, although there is no requirement on ordering.
|
|
So, let's go ahead and move that into our file.
|
|
|
|
```yaml hl_lines="6"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
image: node:12-alpine
|
|
command: sh -c "yarn install && yarn run dev"
|
|
```
|
|
|
|
|
|
1. Let's migrate the `-p 3000:3000` part of the command by defining the `ports` for the service. We will use the
|
|
[short syntax](https://docs.docker.com/compose/compose-file/#short-syntax-1) here, but there is also a more verbose
|
|
[long syntax](https://docs.docker.com/compose/compose-file/#long-syntax-1) available as well.
|
|
|
|
```yaml hl_lines="7 8"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
image: node:12-alpine
|
|
command: sh -c "yarn install && yarn run dev"
|
|
ports:
|
|
- 3000:3000
|
|
```
|
|
|
|
1. Next, we'll migrate both the working directory (`-w /app`) and the volume mapping (`-v $PWD:/app`) by using
|
|
the `working_dir` and `volumes` definitions. Volumes also has a [short](https://docs.docker.com/compose/compose-file/#short-syntax-3) and [long](https://docs.docker.com/compose/compose-file/#long-syntax-3) syntax.
|
|
|
|
One advantage of Docker Compose volume definitions is we can use relative paths from the current directory.
|
|
|
|
```yaml hl_lines="9 10 11"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
image: node:12-alpine
|
|
command: sh -c "yarn install && yarn run dev"
|
|
ports:
|
|
- 3000:3000
|
|
working_dir: /app
|
|
volumes:
|
|
- ./:/app
|
|
```
|
|
|
|
1. Finally, we need to migrate the environment variable definitions using the `environment` key.
|
|
|
|
```yaml hl_lines="12 13 14 15 16"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
image: node:12-alpine
|
|
command: sh -c "yarn install && yarn run dev"
|
|
ports:
|
|
- 3000:3000
|
|
working_dir: /app
|
|
volumes:
|
|
- ./:/app
|
|
environment:
|
|
MYSQL_HOST: mysql
|
|
MYSQL_USER: root
|
|
MYSQL_PASSWORD: secret
|
|
MYSQL_DB: todos
|
|
```
|
|
|
|
|
|
### Defining the MySQL Service
|
|
|
|
Now, it's time to define the MySQL service. The command that we used for that container was the following:
|
|
|
|
```bash
|
|
docker run -d \
|
|
--network todo-app --network-alias mysql \
|
|
-v todo-mysql-data:/var/lib/mysql \
|
|
-e MYSQL_ROOT_PASSWORD=secret \
|
|
-e MYSQL_DATABASE=todos \
|
|
mysql:5.7
|
|
```
|
|
|
|
1. We will first define the new service and name it `mysql` so it automatically gets the network alias. We'll
|
|
go ahead and specify the image to use as well.
|
|
|
|
```yaml hl_lines="6 7"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
# The app service definition
|
|
mysql:
|
|
image: mysql:5.7
|
|
```
|
|
|
|
1. Next, we'll define the volume mapping. When we ran the container with `docker run`, the named volume was created
|
|
automatically. However, that doesn't happen when running with Compose. We need to define the volume in the top-level
|
|
`volumes:` section and then specify the mountpoint in the service config. By simply providing only the volume name,
|
|
the default options are used. There are [many more options available](https://docs.docker.com/compose/compose-file/#volume-configuration-reference) though.
|
|
|
|
```yaml hl_lines="8 9 10 11 12"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
# The app service definition
|
|
mysql:
|
|
image: mysql:5.7
|
|
volumes:
|
|
- todo-mysql-data:/var/lib/mysql
|
|
|
|
volumes:
|
|
todo-mysql-data:
|
|
```
|
|
|
|
1. Finally, we only need to specify the environment variables.
|
|
|
|
```yaml hl_lines="10 11 12"
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
# The app service definition
|
|
mysql:
|
|
image: mysql:5.7
|
|
volumes:
|
|
- todo-mysql-data:/var/lib/mysql
|
|
environment:
|
|
MYSQL_ROOT_PASSWORD: secret
|
|
MYSQL_DATABASE: todos
|
|
|
|
volumes:
|
|
todo-mysql-data:
|
|
```
|
|
|
|
At this point, our complete `docker-compose.yml` should look like this:
|
|
|
|
|
|
```yaml
|
|
version: "3.7"
|
|
|
|
services:
|
|
app:
|
|
image: node:12-alpine
|
|
command: sh -c "yarn install && yarn run dev"
|
|
ports:
|
|
- 3000:3000
|
|
working_dir: /app
|
|
volumes:
|
|
- ./:/app
|
|
environment:
|
|
MYSQL_HOST: mysql
|
|
MYSQL_USER: root
|
|
MYSQL_PASSWORD: secret
|
|
MYSQL_DB: todos
|
|
|
|
mysql:
|
|
image: mysql:5.7
|
|
volumes:
|
|
- todo-mysql-data:/var/lib/mysql
|
|
environment:
|
|
MYSQL_ROOT_PASSWORD: secret
|
|
MYSQL_DATABASE: todos
|
|
|
|
volumes:
|
|
todo-mysql-data:
|
|
```
|
|
|
|
|
|
## Running our Application Stack
|
|
|
|
Now that we have our `docker-compose.yml` file, we can start it up!
|
|
|
|
1. Make sure no other copies of the app/db are running first (`docker ps` and `docker rm -f <ids>`).
|
|
|
|
1. Start up the application stack using the `docker-compose up` command. We'll add the `-d` flag to run everything in the
|
|
background.
|
|
|
|
```bash
|
|
docker-compose up -d
|
|
```
|
|
|
|
When we run this, we should see output like this:
|
|
|
|
```plaintext
|
|
Creating network "app_default" with the default driver
|
|
Creating volume "app_todo-mysql-data" with default driver
|
|
Creating app_app_1 ... done
|
|
Creating app_mysql_1 ... done
|
|
```
|
|
|
|
You'll notice that the volume was created as well as a network! By default, Docker Compose automatically creates a
|
|
network specifically for the application stack (which is why we didn't define one in the compose file).
|
|
|
|
1. Let's look at the logs using the `docker-compose logs -f` command. You'll see the logs from each of the services interleaved
|
|
into a single stream. This is incredibly useful when you want to watch for timing-related issues. The `-f` flag "follows" the
|
|
log, so will give you live output as it's generated.
|
|
|
|
If you don't already, you'll see output that looks like this...
|
|
|
|
```plaintext
|
|
mysql_1 | 2019-10-03T03:07:16.083639Z 0 [Note] mysqld: ready for connections.
|
|
mysql_1 | Version: '5.7.27' socket: '/var/run/mysqld/mysqld.sock' port: 3306 MySQL Community Server (GPL)
|
|
app_1 | Connected to mysql db at host mysql
|
|
app_1 | Listening on port 3000
|
|
```
|
|
|
|
The service name is displayed at the beginning of the line (often colored) to help distinguish messages. If you want to
|
|
view the logs for a specific service, you can add the service name to the end of the logs command (for example,
|
|
`docker-compose logs -f app`).
|
|
|
|
!!! info "Pro tip - Waiting for the DB before starting the app"
|
|
When the app is starting up, it actually sits and waits for MySQL to be up and ready before trying to connect to it.
|
|
Docker doesn't have any built-in support to wait for another container to be fully up, running, and ready
|
|
before starting another container. For Node-based projects, you can use the
|
|
[wait-port](https://github.com/dwmkerr/wait-port) dependency. Similar projects exist for other languages/frameworks.
|
|
|
|
1. At this point, you should be able to open your app and see it running. And hey! We're down to a single command!
|
|
|
|
## Seeing our App Stack in Docker Dashboard
|
|
|
|
If we look at the Docker Dashboard, we'll see that there is a group named **app**. This is the "project name" from Docker
|
|
Compose and used to group the containers together. By default, the project name is simply the name of the directory that the
|
|
`docker-compose.yml` was located in.
|
|
|
|
|
|
|
|
If you twirl down the app, you will see the two containers we defined in the compose file. The names are also a little
|
|
more descriptive, as they follow the pattern of `<project-name>_<service-name>_<replica-number>`. So, it's very easy to
|
|
quickly see what container is our app and which container is the mysql database.
|
|
|
|
|
|
|
|
|
|
## Tearing it All Down
|
|
|
|
When you're ready to tear it all down, simply run `docker-compose down` or hit the trash can on the Docker Dashboard
|
|
for the entire app. The containers will stop and the network will be removed.
|
|
|
|
!!! warning "Removing Volumes"
|
|
By default, named volumes in your compose file are NOT removed when running `docker-compose down`. If you want to
|
|
remove the volumes, you will need to add the `--volumes` flag.
|
|
|
|
The Docker Dashboard does _not_ remove volumes when delete the app stack.
|
|
|
|
Once torn down, you can switch to another project, run `docker-compose up` and be ready to contribute to that project! It really
|
|
doesn't get much simpler than that!
|
|
|
|
|
|
## Recap
|
|
|
|
In this section, we learned about Docker Compose and how it helps dramatically simply the defining and
|
|
sharing of multi-service applications. We created a Compose file by translating the commands we were
|
|
using into the appropriate compose format.
|
|
|
|
At this point, we're starting to wrap up the tutorial. However, there are a few best practices about
|
|
image building we want to cover, as there is a big issue with the Dockerfile we've been using. So,
|
|
let's take a look! |