Return 400 for invalid instance registration payloads

[amacharla15]

Summary:

Map invalid /instances registration payloads to 400 BAD_REQUEST instead of surfacing as 500.

Add integration tests covering invalid JSON, missing name, and missing healthUrl.

How to run:

./mvnw -pl spring-boot-admin-server -Dtest=InstancesControllerIntegrationTest test

Evidence:

Before: invalid registration could surface as 500.

Now: tests fail if invalid payloads don’t return 400.

[SteKoe]

Hi @amacharla15,

thanks for your PR! I very much like that you have provided backend tests. I have got some questions, though:

• What is the purpose of test frontend test?
• What is the purpose of mapping.json?
• What is your reason for not using spring-boot-starter-validation alongside @Valid in Controller as well as @NotBlank on targeted fields in Registration.java and get rid of ControllerAdvice?

[SteKoe]

See comment above.

[amacharla15]

Hi @SteKoe — Apologies and thanks for the review and the questions.

Purpose of the frontend test
There is no intended purpose for a frontend test in this PR. That file was an accidental artifact from my local exploration when I was reproducing the behavior and verifying UI impact. I agree it should not be part of this backend-focused change. I will remove it from the PR so the scope stays strictly server-side.

Purpose of mappings.json
Same situation: mappings.json was not meant to be included. It is related to local mock/test setup (WireMock/MSW-style mapping artifacts) and is not required for the server fix or the integration tests validating /instances. I will remove it from the PR.

Why I didn’t use spring-boot-starter-validation + @Valid/@notblank
My initial goal was to keep the production change minimal and explicitly map the observed failure mode (invalid registration surfacing as 500) to a 400 via a controller advice, while locking it in with integration tests.
That said, I agree your suggestion is cleaner and more idiomatic: using spring-boot-starter-validation with @Valid on the controller input + @notblank on the relevant fields should enforce request validation at the right layer and avoid the need for custom ControllerAdvice. I will update the PR to use standard bean validation and remove the advice if it becomes unnecessary, while keeping the same integration tests to guarantee the 400 contract.

Additionally, I will rebase the branch onto the current codecentric:master so the PR is no longer out-of-date and CI can run cleanly.