> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ergomake.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Your first preview using compose

> Learn how to integrate with GitHub pull requests to create your first automatic preview.

Ergomake uses `docker-compose.yml` files to set up previews.

In this page, you'll learn how to set-up your first preview using a `docker-compose.yml` file.

## Getting started

1. [Log into the Ergomake dashboard](https://app.ergomake.dev).

2. Select the desired organization and click the "Add Repository" button.

3. During the installation process, you'll be prompted to give it access to the repository for which you want to generate previews.
   **Make sure to select all the repositories you need**.

   > ⚠️ Ergomake can't generate previews if it doesn't have access to a repository.

4. Open a pull request adding a `docker-compose.yml` file to a `.ergomake` folder in the root of your repository.

   > At this point, you should already receive a preview link in this pull request.

   ```yml theme={null}
   # Here's an example docker-compose.yml file
   version: "3.8"
   services:
     # On pull-requests, Ergomake can build your own images
     web:
       build: ./frontend
       ports:
         - "8080:8080"
        labels:
          # This label will cause Ergomake to set, during build time,
          # REACT_APP_API_URL to the address of the API service (https),
          # followed by "/prefix"
          dev.ergomake.env.replace-arg.REACT_APP_API_URL: 'https://{{ services.api.url }}/api'

     # You can build a second repository by referencing a folder with
     # the desired repository name in a path *outside* your current repository.
     api:
       build: ../../my-backend-repo
       ports:
         - "3001:3001"

     database:
       image: mongo
       environment:
         MONGODB_INITDB_ROOT_USERNAME: username
         MONGODB_INITDB_ROOT_PASSWORD: password
   ```

5. Merge Ergomake's PR once you're happy with how the preview looks.

## Writing Dockerfiles

Writing Dockerfiles tends to be the most difficult part of setting up previews using `docker-compose.yml`.

To learn more about how to write them, see [*Writing Dockerfiles*](/dockerfiles).