4.x [docs] MP does not handle built-in services (e.g. health) if user has resource with path /

[tjquinno]

Environment Details

• Helidon Version: 4.x
• Helidon MP
• JDK version:
• OS:
• Docker version (if applicable):

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Problem Description

In 3.x, a user could have an MP resource with path / and Helidon-provided services such as /metrics would still work.

In 4.x , if the user has a resource with / Helidon incorrectly routes requests for the Helidon-provided services to the user's / resource.

This is a major breaking change.

Steps to reproduce

1. In the 3.x MP QuickStart example, change the path on GreetResource from /greet to /, rebuild, run, and access curl http://localhost:8080/metrics. It works. curl http://localhost:8080/ and /Joe acts as they should: greetings to "World" and "Joe" respectively.
2. In the 4.x MP QuickStart example, change the path the same way, build, and run. The greeting requests work but accessing /metrics gives you "Hello metrics" instead of the actual metrics response.

[tjquinno]

See also #8550

There should be a nice way to resolve this by setting the following config in microprofile-config.properties:

server.features.observe.weight = 120

or, equivalently, in SE config:

server:
  features:
    observe:
      weight: 120

There is a bug (see above link) currently preventing this from working in 4.x but it is being actively worked.

[tjquinno]

Keeping this issue open for adding doc describing the weighting technique.

Also, the MP doc does not have an observability page and should. That'll be part of this issue as well.