balance: Specialize the balancer for P2C #288
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As described in tower-rs#286, `Balance` had a few problems: - it is responsible for driving all inner services to readiness, making its `poll_ready` O(n) and not O(1); - the `choose` abstraction was a hinderance. If a round-robin balancer is needed it can be implemented separately without much duplicate code; and - endpoint errors were considered fatal to the balancer. This changes replaces `Balance` with `P2CBalance` and removes the `choose` module. Endpoint service failures now cause the service to be removed from the balancer gracefully. Endpoint selection is now effectively constant time, though it biases for availability in the case when random selection does not yield an available endpoint. `tower-test` had to be updated so that a mocked service could fail after advertising readiness.
olix0r
commented
May 30, 2019
The balance layer now operates over MakeP2CBalance, which composes over layers that produce Discover instances.
hawkw
approved these changes
May 30, 2019
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Per offline discussion, @carllerche suggested some potential improvements that I have written up in #292. We're going to merge this for the time being and revisit #292 before balance is released to crates. |
olix0r
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Jun 5, 2019
tower-rs/tower#288 changed the Balance implementation substantially so that it is no longer responsible for driving services to readiness. Instead, a new layer, `spawn_ready` is inserted around endpoint stack to ensure that readiness is driven on a background task. In support of this change, the `pending` layer was removed from the enpdoint stack and, instead, the discovery system is now responsible for driving pending services to be materialized.
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I just realized that this does introduce a requirement for inner services to implement |
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@jonhoo yeah, that is a notable change... I think it would be pretty easy to introduce a |
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@jonhoo though, note the |
olix0r
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Jul 11, 2019
tower-rs/tower#288 and tower-rs/tower#293 changed the Balance implementation substantially. Now, a new layer, `spawn_ready` is inserted around endpoint stack to ensure that readiness is driven on a background task. In support of this change, the `pending` layer was removed from the endpoint stack and, instead, the discovery system is now responsible for driving pending services to be materialized.
panthervis
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Oct 8, 2021
tower-rs/tower#288 and tower-rs/tower#293 changed the Balance implementation substantially. Now, a new layer, `spawn_ready` is inserted around endpoint stack to ensure that readiness is driven on a background task. In support of this change, the `pending` layer was removed from the endpoint stack and, instead, the discovery system is now responsible for driving pending services to be materialized.
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As described in #286,
Balancehad a few problems:its
poll_readyO(n) and not O(1);chooseabstraction was a hinderance. If a round-robin balanceris needed it can be implemented separately without much duplicate
code; and
This changes replaces
Balancewithp2c::Balanceand removes thechoosemodule.Endpoint service failures now cause the service to be removed from the
balancer gracefully.
Endpoint selection is now effectively constant time, though it biases
for availability in the case when random selection does not yield an
available endpoint.
tower-testhad to be updated so that a mocked service could fail afteradvertising readiness.