Add documentation around `backend.startup` configuration

[awanlin]

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🗃️ Project Area

Documentation

🔗 External Integration

N/A

📝 Description

There are currently no docs on the backend.startup configuration. The code for this is well documented but it would be nice to have proper docs with some basic examples

Config code:

backstage/packages/backend-app-api/config.d.ts

Line 27 in 1a8de99

startup?: {

These docs should be added here, somewhere at the bottom for now: https://backstage.io/docs/backend-system/building-backends/index

Have you read the Code of Conduct?

• I have read the Code of Conduct

Are you willing to submit PR?

No, but I'm happy to collaborate on a PR with someone else

[SatyamKumarCS]

Hi! I'd love to work on this.

I've read through the config code at packages/backend-app-api/config.d.ts and the existing backend system docs at https://backstage.io/docs/backend-system/building-backends/index — I have a clear picture of what's missing.

My plan:

1. Document the startup configuration block with a description of each field
2. Add a basic example showing how to configure it in app-config.yaml
3. Place it at the bottom of the linked docs page as suggested

Since you mentioned you're happy to collaborate, would you be open to reviewing a draft before I open the PR? Happy to keep the scope tight and focused.

Could you assign this to me, or let me know if it's still available?