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
