Are you by any chance using Keycloak 21? Because they have removed curl from the image, so the health check fails. I had the same issue when upgrading from 19. Will update the article with the solution.

Edit: It is now updated, see the Dockerfile. You must add a bit to install curl in the image. Then the health check should succeed.

There is two potential issues. You have an extra slash behind health, I think you must strip that (only required if you use a 200 OK from /auth as health check). Using /auth would require you to set the environment variable KC_HTTP_RELATIVE_PATH to /auth (you should only do this if migrating and you do not want to update urls, not from fresh install, since /auth is stripped now). And using /health requires you to set the KC_HEALTH_ENABLED to true.