When moving the reservation of a claim for a pod into the PreBind phase in a
future commit, multiple different update attempts will be executed
concurrently. We want an attempt to succeed if and only if adding the entry
passes validation. Without patch strategy and key, strategic-merge-patch
replaces the entire ReservedFor instead of adding new entries.
Server-side-apply cannot be used because each attempt may start with a stale
ResourceClaim (thus cannot send the entire ReservedFor) and SSA doesn't support
merging when using the same manager string. Using different managers (one for
each entry) would work, but sounds like a bad hack.
This assumes that any such field is atomic, except:
* OwnerReferences: because it has a `+patchStrategy=merge`, but it
probably needs a `+listMapKey=...` ?
* Finalizers: because it hs a `+patchStrategy=merge`, but is a
primitive type (string).
* []byte fields, which should not be failing this anyway (fixed
subsequently).
An alternative approach could be just to turn off the API warnings for
these fields, but it felt more correct to declare the semantics.
The "set" list type was chosen because it seemed appropriate (no duplicates!)
but that made tracking of managed fields more expensive (each entry in the list
is tracked, not the entire field) and for no good reason (one client is
responsible for the entire list).
Therefore the type gets changed to "atomic". Server-side-apply has not been
used in the past and PodSchedulingContext objects are short-lived and still in
alpha, so the any potential compatibility issues should be minor.
The scheduling throughput in scheduler_perf increases:
name old SchedulingThroughput/Average new SchedulingThroughput/Average
PerfScheduling/SchedulingWithResourceClaimTemplate/2000pods_100nodes-36 18.8 ± 8% 24.0 ±37%
PerfScheduling/SchedulingWithMultipleResourceClaims/2000pods_100nodes-36 13.7 ±81% 18.5 ±40%
