Coverage for server / utilities / redis_url.py: 100%

1"""Resolve ``REDIS_URL``, and make a fallback to localhost audible. 

2 

3A SILENT fallback is how the platform lost a response cache for three months and 

4left two Celery workers consuming from a local broker from March to September: an 

5unset ``REDIS_URL`` connected SUCCESSFULLY to a local Redis, so every health check 

6passed while the service was pointed at the wrong thing. 

7 

8Every host is now consolidated onto ``redis.mathmattersqa.com`` and no server runs 

9a local Redis, so reaching this fallback on a deployed host means "misconfigured" 

10-- never "local dev". 

11 

12Deliberately a warning and not a hard failure: local development legitimately uses 

13localhost, and turning a missing variable into an import-time crash would trade a 

14quiet problem for a loud outage. 

15 

16Developer: Allan Ninal 

17""" 

18 

19import logging 

20import os 

21 

22logger = logging.getLogger(__name__) 

23 

24_warned = False 

25 

26 

27def redis_url_or_default(default: str) -> str: 

28 """Return ``REDIS_URL``; warn once if falling back to ``default``.""" 

29 global _warned 

30 

31 url = os.getenv("REDIS_URL") 

32 if url: 

33 return url 

34 

35 if not _warned: 

36 _warned = True 

37 logger.warning( 

38 "REDIS_URL is not set; falling back to %s. That is correct for LOCAL " 

39 "DEVELOPMENT only -- no server runs a local Redis, so on a deployed host " 

40 "this means the service is misconfigured and is NOT talking to the shared " 

41 "instance.", 

42 default, 

43 ) 

44 return default