xds-client/retry: add jitter to connection backoff#2738
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Randomize each backoff delay by a configurable factor (gRFC A6) so reconnecting clients don't retry in lockstep. Default jitter is 0.2 (±20%); `with_jitter` validates the factor is in [0.0, 1.0] and 0.0 disables it. Adds the `rand` dependency.
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Motivation
The reconnect backoff was fully deterministic: every client that lost its xDS stream at the same time (control-plane restart or a network blip) computed the identical delay schedule and retried in lockstep. That synchronized retry storm hammers the management server right when it's least able to absorb it.
Solution
Randomize each delay by a configurable factor per gRFC A6 so clients spread their reconnects across a window instead of colliding. Default jitter is 0.2 (±20%) ;
with_jittervalidates the factor is in [0.0, 1.0], and 0.0 restores the old deterministic behavior.Random
I hesitated between
randcrate andfastrand, in the end I fallback to the same dep grpc is already using for the jitter in named_resolution