Why are my Google AppEngine instances crashing with 'error code 121'?

Question

I have been running a java high-replication web application on Google AppEngine for some time now. About two days ago - basically out of nowhere - a lot of requests began to fai

Answer 1

I don't have enough points to reply but I have a specific use case that seems interesting:

• python27
• hrd
• dynamic backed configured with 8 instances

Everything works as expected, except for one instance, instance=2, which basically cycles

• '/_ah/start'
• (Error code 121)
• '/_ah/stop'

Backends allows you to address a specific instance such as 2.backendname.appname.appspot.com and apparently something is wrong with that instance.

I suppose it's reassuring to know that there's one bad instance that's repeatedly failing due to a vague error code, instead of many instances failing randomly due to a vague error code. It'd be more reassuring if that instance were dropped, etc particularly if it's cycling this pattern.