Structure

Every application you deploy on Platform.sh is built as a virtual cluster, containing a series of containers. The master branch of your Git repository is always deployed as a production cluster. Any other branch can be deployed as a development cluster. By default you can have up to three live development clusters at once but you can buy more on a per-project basis.

There are three types of containers within your cluster: One Router, one or more Applications, and zero or more Services. When deployed, they conceptually look like this:

All of those containers are managed by three special files in your Git repository: .platform/routes.yaml, .platform/services.yaml, and .platform.app.yaml.

In most cases, that means your repository will look like this:

yourproject/
  .git/
  .platform/
    services.yaml
    routes.yaml
  .platform.app.yaml
  <your files here>

Router

There is always exactly one Router per cluster. The Router of a cluster is a single nginx process. It is configured by the routes.yaml file. Its purpose is to map incoming requests to an Application container, and to provide basic caching of responses if so configured. It has no persistent storage.

Service

Service containers are configured by the services.yaml file. There may be zero or more service containers in a cluster, depending on the services.yaml file. The code for a Service is provided by Platform.sh in a pre-built container image, along with default configuration. Depending on the service it may also have user-provided configuration in the services.yaml file. Examples of services include MySQL/MariaDB, Elasticsearch, Redis, and RabbitMQ.

Application

There is always at least one Application container per cluster, but there may be more. Each application container corresponds to a .platform.app.yaml file in the repository. If there are 3 .platform.app.yaml files, there will be three Application containers. Application containers hold the code you provide via your Git repository. Application containers are always built off of one of the Platform.sh-provided language-specific images, such as “PHP 5.6”, “PHP 7.2”, or “Python 3.6”. And different application containers can be running different languages or versions.

For most typical applications there is only one .platform.app.yaml file, which is generally placed at the repository root.