Support for environment variables

[tobiasqueck]

Is your feature request related to a problem? Please describe.

I would like to have an out of the box supported standard approach to use environment variables to configure my middlewares and tasks.

Why? As one of the maintainers of the middleware in the open-ux-tools, I have noticed a repetitive pattern: usage of environment variables. In nearly all our middlewares/tasks we support some kind of usage of environment variables as input. A quick search through other middlewares also shows that we are not the only ones but many others also have their way of allowing to provide parts of the configuration as env variables.
The problem is that everybody does their own thing leading to inconsistencies of how to use env variables.

Describe the solution you'd like

I'd prefer a very simple solution allowing me to define environment variable placeholders in my yaml e.g.

server:
  customMiddleware:
  - name: preview-middleware
    afterMiddleware: compression
    configuration:
      debug: ${DEBUG}

The UI5 CLI should resolve the environment variable before calling my middleware so that the middleware implementation does not have to bother.
Please also support dotenv out of the box as part of the same feature.

Describe alternatives you've considered

No.

Additional context

No.

[d3xter666]

Hi @tobiasqueck ,

Thank you for your proposal!

[fkolar]

I understand that every environment needs to deal with its own specifics. So for the LOCAL dev you might have to set different URLs or any kinds of constants that are different to TEST or PROD. There needs to be a way to support this.

• Some teams might use custom middleware, but that might be just to deal with rerouting one URLs to the another
• Having placeholders and storing actual values in the .env specific files

I believe this is something that should be supported by default.

For the placeholders I found this ui5-string-replacer or this one with this custom middleware , the same goes for this community string replacer.

What to use?

[RandomByte]

@tobiasqueck, @menof36go and others:

The example above shows a custom middleware configuration. Do you have specific use cases for using environment variable substitutions in other places of the ui5.yaml? We have some concerns that lead us wondering whether this feature should be restricted to custom middleware configuration for the time being.

[marianfoo]

I want to build my app for different customers. So I test this with middleware and then build and deploy with different parameters.
So Middleware and build is used for one app. Build and deploy for example to different packages and/or transports and other variables.
If you use this only for Middleware I still have one yaml for each customer.
It only reduces my mock yaml to one file.

[RandomByte]

Thanks @marianfoo. So besides custom middleware, you also need to change the configuration of custom tasks (but no standard tasks)?

I guess inheritance between ui5.yaml files would still be the better solution for your use case?

[marianfoo]

Correct, currently only parameters with custom task.
Inheritance or cli Parameter would also work.

[tobiasqueck]

When requesting the feature I was only thinking about customTasks and customMiddlewares. Now, I'd add customConfiguration. I don't have use cases for other parts of the config.

[flovogt]

We track this enhancement request SAP internally in backlog item CPOUI5FOUNDATION-919.