04 7 / 2017
If you use Google cloud with Docker and are suddenly seeing an invalid_grant error, restart docker first!
May be this helps someone from hours of frustration and pointless debugging! A working piece of code suddenly started throwing ‘invalid_grant’ errors and after debugging for hours (IAM permissions, matching secret keys, extreme logging, and what not!) I finally realized that the time in docker container was behind my system time, and that was causing the errors. Looks like it is some docker bug which people are talking about here:
https://forums.docker.com/t/time-in-container-is-out-of-sync/16566
Restarting docker fixed it instantaneously. So if you ever find yourself in the above situation (or similar situation where a third party API call suddenly starts failing withing a docker container), restart docker before doing anything else.