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