closes AE-494
[skip-stages=Flakey]
[skip-crystalball]
several things going on here. in general, many of our monkeypatches
have been implemented in upstream, but in a vastly different way, so
we need to enable/configure those things
* `servers` is no longer accepted as a backwards compatible
configuration option; use `url`
* `database` is no longer accepted as a backwards compatible
configuration option; you _can_ use `db`, but preferable to
just use `url`
* no longer merge together redis.yml and cache_store.yml; if one
references the other, simply use the config from the other
* `nil_store` is no longer accepted as a backwards compatible
configuration option; use `null_store` (almost no one should
be explicitly using this anyway, so nbd)
* automatically not-even-trying when redis has previously failed
is now handled by redis-client's circuit breaker. be sure to
configure it in redis.yml/cache_store.yml/dynamic settings
* ignoring redis failures completely is already done by
RedisCacheStore; just rely on that, except for the few cases
where we use redis directly. some of these now take advantage
of a new `failsafe` kwarg (and often in combination with
pipelining), and some just handle it directly
* move logging to a RedisClient middleware
* move Twemproxy disallowed commands to a RedisClient middleware
* simplify Canvas.lookup_cache_store to have far less special casing
(in particular, patching is done automatically now)
* add ability to use Redis::Cluster (configure with `nodes` instead
of `url`)
* still override Redis::Distributed's HashRing, so that we don't
change our ring layout with the new MD5 hashing for servers. but
we got to vastly simplify the new class, due to upstream
refactorings allowing us to simply override a single method rather
than having to re-implement the entire class
* statsd reporting of redis errors is now simply passed as a callback
to RedisCacheStore, breaking CanvasCache's dependency on InstStatsd
Change-Id: I787672677a21994d40ae304dbac0fbf3a960a779
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/325641
Reviewed-by: Jacob Burroughs <jburroughs@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
Build-Review: Cody Cutrer <cody@instructure.com>
88a5803982