[RFC] Fallback mechanism for SingleFlight about athens HOT 2 OPEN

I am not sure this will work. Consider You have 3 nodes behind an LB. If redis fails and then you have in-memory singleflight request, you may still get 3 single flight requests overwriting each other. I am not sure if there is a good way to guarantee uniqueness.

the easiest way is to probably write a new singleflight type backed by a managed by a cloud provider just like storage.

from athens.

Consider You have 3 nodes behind an LB. If redis fails and then you have in-memory singleflight request, you may still get 3 single flight requests overwriting each other.

Yes if the fallback is configured to use in-memory then that's the expected behaviour after this implementation. The idea is to let it work even after redis is down, currently it doesn't work at all.

you may still get 3 single flight requests overwriting each other. I am not sure if there is a good way to guarantee uniqueness.

Also, like I described above - another distributed store (redis/ etcd etc.) can also be used as fallback so it can still guarantee uniqueness, it would just depend on your config.

Basically there're 3 possible scenarios:

• Fallback configured to "none": Don't use any fallback and return an error like the current behavior.
  • Mainly for backwards compatibility or if you'd like to keep things simple and are okay with handling these situations manually.
• Fallback configured to "memory": Fallback to memory until the distributed store is up. Athens will continue working but distributed singleflight won't work.
  • Use this If you'd want Athens to continue working without distributed locking.
• Fallback configured to "etcd/redis/etc.": Fallback to another distributed cache until the primary one is up. Athens will continue working and distributed singleflight will also work.
  • Use this If you'd want Athens to continue working with distributed locking and are okay with maintaining a secondary distributed store.

So based on the resiliency requirements of the users they will be able to configure Athens accordingly.

from athens.