There was nothing RESTful or well planned about this API’s interfaces, and the work to do something like that would have been nontrivial. Management never prioritized the work.

At a prior job, our API load balancers would swallow all errors and return an HTTP 200 response with no content. It was because we had one or two clients with shitty integrations that couldn’t handle anything but 200. Of course, they brought in enough money that we couldn’t ever force them to fix it on their end.

Are you able to independently confirm that the domaincheck container is listening to the right port? Eg netstat -tunlp on the host