Readiness API responds with HTML

Summary

The /-/readiness endpoint returns a Something went wrong (500) error.

What is the current bug behavior?

During errors that disrupt Gitlab normal operations, a 500 error HTML page is displayed instead of a JSON document. From documentation, it seems this is as expected - https://docs.gitlab.com/ce/user/admin_area/monitoring/health_check.html. It seems illogical to display a 500 error instead of continuing to display a JSON document with the related checks.

What is the expected correct behavior?

• Add logging to continue reporting the readiness checks when an 500 error occurs.
• Continue to display the /-/readiness JSON payload, ignoring the 500 error page.