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Prepare to Use Release
In order to use Release, you must meet the prerequisites mentioned in Release overview.
Release supports building and running complex applications. Release requires a docker-compose.yml , package.json , or .release.yaml file to be in the root of your application's Git repository. Release uses these files to generate the Application Template that is used as a blueprint to build your environments.
If your application has nested directories where your docker-compose.yaml or package.json files reside, you can add a .release.yaml file to the root of your repository to tell Release where these files are located. See The .release.yaml file reference guide for more information.
We recommend using a monorepo and a directory-per-service at the project root when your application requires two or more services. Here is an example directory structure for three services that require docker builds:
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├── README.md
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├── docker-compose.yml
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├── result
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│ └── Dockerfile
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├── vote
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│ └── Dockerfile
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└── worker
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└── Dockerfile
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If you're not using a monorepo, you can create an application for each repository and connect them using environment variables in each of those applications. See Microservices architecture for more information.

Testing Docker Compose for Release

The best way to test if your application will run in Release is to get Docker Compose to run your application locally. See Overview of Docker Compose for more details.
Release allows you to quickly spin up containerized services without the traditional wait times involved with cloud-native services.
When running an application locally or in a Release ephemeral environment, we recommend that you isolate your application's external dependencies. Consider using off-the-shelf Docker images to represent the cloud-native services that your application depends on, such as Postgres, Redis, etc. Visit Docker Hub to find many off-the-shelf Docker images.
You can use environment variables to connect ephemeral environments to AWS-native services such as RDS, however, we recommend using these off-the-shelf Docker images to speed up deployment and simplify set up.
This is an example of a docker-compose.yml file that builds three Docker images and leverages two off-the-shelf containers for Redis and Postgres:
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version: "3"
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services:
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vote:
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build: ./vote
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command: python app.py
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volumes:
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- ./vote:/app
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ports:
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- "5000:80"
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depends_on:
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- "worker"
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result:
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build: ./result
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command: nodemon server.js
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volumes:
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- ./result:/app
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ports:
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- "5001:80"
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depends_on:
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- "worker"
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worker:
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build:
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context: ./worker
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depends_on:
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- "redis"
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- "db"
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redis:
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image: redis:alpine
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container_name: redis
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db:
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image: postgres:9.4
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container_name: db
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volumes:
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- "db-data:/var/lib/postgresql/data"
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volumes:
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db-data:
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Release detects many popular services such as Redis, MySQL, Postgres, RabbitMQ, and many more, and will handle opening standard ports for these services.
Here's an example of adding Redis, RabbitMQ, and Memcached with minimal configuration in Docker Compose:
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version: "3"
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services:
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redis:
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image: "redis:5-alpine"
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rabbitmq:
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image: "rabbitmq:3.7-alpine"
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memcached:
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image: "memcached:1.5-alpine"
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Building your application

Release supports most options from docker-compose build. Release looks for all services with a build stanza, and executes a docker build for each service found.

Specify the current working directory:

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version: "3"
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services:
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app:
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build: .
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Specify a different directory to build:

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version: "3"
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services:
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vote:
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build: ./vote
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Specify the Dockerfile and pass in build arguments:

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version: "3"
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services:
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mysql:
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build:
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context: .
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dockerfile: Dockerfile-mysql
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args:
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S3_BUCKET: "data.example.com"
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MYSQL_VERSION: "5.7"
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Release ports and DNS hostnames

Release uses the docker-compose ports (HOST:CONTAINER) definition to determine when a service should be exposed to the internet. When Release encounters a service with a HOST:CONTAINER definition, it creates a NodePort, load balancer rule, and DNS hostname entry for the service.
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version: "3"
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services:
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frontend:
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build:
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context: .
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dockerfile: Dockerfile-frontend
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ports:
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- "8080:8080"
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command: ["npm", "run", "dev-server-docker"]
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In this example, Release creates a hostname for the frontend service that exposes port 8080.
Internal services, like your data stores, caches, and background workers, should not be exposed to the internet, and should only be available internally to other services defined in your docker-compose.
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version: "3"
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services:
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db:
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image: postgres:9.4
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ports:
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- "5432"
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This example shows Postgres opening a container port on 5432 that another service can consume.

Environment variables

Most applications use environment variables to define how services talk to each other and/or change the behavior of an application in a given environment. Release uses the environment variables provided in your docker-compose as a starting point. All of the environment variables for each service defined in your docker-compose are loaded into Release when you initially create an application. Release supports all of the standard docker-compose mechanisms for defining environment variables.
You can use env file to specify an external env file:
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version: "3"
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services:
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api:
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build:
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context: ./api
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dockerfile: Dockerfile.django
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ports:
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- "8000:8000"
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env_file: .env
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You can also set environment variables directly in your docker-compose file:
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version: "3"
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services:
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nginx:
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build: .
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ports:
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- "5000:5000"
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environment:
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- AWS_REGION=us-west-2
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- AWS_SECRET_ACCESS_KEY=XXX
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- RESOLVER=8.8.8.8
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If you have dynamic or secret environment variables, you can read more about environment-specific environment variables in our reference guide.