GEP: Configurable Retries in HTTPRoute

[robscott]

What would you like to be added:
I would like to be able to configure the following in HTTPRoute:

1. The max number of times to retry a request
2. The reason(s) and/or status codes a request should be retried
3. The timeout for each retry attempt

I believe all 3 of these would be implementable for Envoy based implementations, the first 2 would be implementable for HAProxy based implementations, unclear what would be implementable for NGINX or others (cc @pleshakov @shaneutt).

Why this is needed:
This is a common feature request and represents a concept that would likely get tied to a variety of custom policies if we did not include it in the main API.

[Xunzhuo]

/assign
/remove-help

[kflynn]

@robscott, on the mesh front, Linkerd actually doesn't support the fixed-number-of-retries concept. Instead there's a retry budget: if your retry budget is e.g. 20%, then as long as not more than 20% of your request volume is retries, Linkerd can continue retrying.

It would be lovely to be able to configure that form of retry, too, without having to resort to crazy custom stuff. Just to complicate your life. 😉

[bowei]

That's a very interesting approach. Is the 20% calculated "globally" or on a-per proxy basis? This may be difficult for more distributed proxy systems to do for a global percentage.

[dprotaso]

@kflynn does setting 0% disable retries?