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

# Dependencies and service discovery

> Order cooperating applications and connect them inside a workspace.

## Declare relationships

In a multi-app manifest, set `dependsOn` to app map keys. Dependencies are deployed before dependents. Unknown dependencies and cycles are configuration errors.

```yaml theme={null}
apps:
  api:
    path: ./api
    port: 5100
    install: npm ci
    start: npm start
    env: { PORT: "5100" }
  web:
    path: ./web
    port: 5101
    install: npm ci
    start: npm start
    env: { PORT: "5101" }
    dependsOn: [api]
    visibility: public
```

For the incremental release path, declare the backend URL explicitly in the dependent app's environment:

```yaml theme={null}
env:
  PORT: "5101"
  RIGBOX_API_URL: http://127.0.0.1:5100
```

`dependsOn` orders applications; the reviewed incremental implementation does not automatically inject the catalog/image flow's service-discovery environment variables. Set the variable name your server code reads and keep the URL aligned with the backend port.

## Connect from the server

Read the declared variable in the frontend's server process and proxy requests to the API. Do not send a loopback URL to browser JavaScript: there it points to the visitor's computer. Keep the backend route private when only sibling services need it.

## Verify

Deploy from the root directory, inspect both app outcomes, and exercise a frontend operation that calls the backend. If it fails, check the dependency name, listening port, and server environment, then read the failing app's logs. The [todo example](https://github.com/rigbox-dev/rigbox-examples/tree/2612ffc9138d3b2f8169b10e3a54abd5495db8b8/todo-app) demonstrates this pattern.

Dependencies between apps differ from [dependency cache inputs and outputs](/deploy/build-cache), which describe installed files.