AE: use stale requests when performing full sync #5873
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Read requests performed during anti antropy full sync currently target the leader only. This generates a non-negligible load on the leader when the DC is large enough and can be offloaded to the followers following the "eventually consistent" policy for the agent state. We switch the AE read calls to use stale requests with a small (2s) MaxStaleDuration value and make sure we do not read too fast after a write.
pierresouchay
approved these changes
May 28, 2019
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This reduces a bit the amount of leader-only RPC and is failry easy to integrate.
On a large cluster, ie: 8000 nodes, this accounts for 8000 / (7 * 60) ~ 20 qps only for anti-entropy when nothing happens (I am not talking about restart of agents).
Using it with stale would allow all reads to scale reads across all consul servers followers more easily. Since MaxStaleDuration is used, we are sure that a late follower will not break registration globally anyway.
hanshasselberg
approved these changes
Jun 17, 2019
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Read requests performed during anti antropy full sync currently target
the leader only. This generates a non-negligible load on the leader when
the DC is large enough and can be offloaded to the followers following
the "eventually consistent" policy for the agent state.
We switch the AE read calls to use stale requests with a small (2s)
MaxStaleDuration value and make sure we do not read too fast after a
write.