the service can be found through'/catalog/service/', but the service is still called 503

Problem Description:
After our service is started, it can be accessed in the form of ip:port, and the service can also be found from consul through'/catalog/service/', but it will last for a period of time when called by the load balancing client 503.

I would like to ask which API can accurately determine whether the service is available, or what other methods can accurately determine whether the service is already available.

No files or tests are named. Start with the /catalog/service/ request and the load-balancing client's 503 window; reproduce the timing and determine which availability signal is authoritative. Done means the reliable check or remaining limitation is identified and documented.

Written by the indexing model from the issue text.