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fix: unavailable stable RS was not scaled down to make room for canary #739

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merged 2 commits into from Sep 28, 2020
Merged

fix: unavailable stable RS was not scaled down to make room for canary #739

merged 2 commits into from Sep 28, 2020

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jessesuen
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@jessesuen jessesuen commented Sep 27, 2020 •
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This is an alternative fix for the issue described in #735

Scenario:

  1. Apply a "bad" rollout (with or without steps) with an image which will crashloopbackoff, and the following surge/unavailable:
spec:
  replicas: 4
  strategy:
    canary:
      maxSurge: 1
      maxUnavailable: 0
  1. Update rollout with a new spec which will not crash
  2. Rollout will surge up, such that there are 5 total replicas (1 new, 4 old)
  3. Currently, rollout will now be stuck forever never being able to reach the second revision, because the controller decides it cannot scale down the stableRS (even when it should).

The correct behavior should be that the Rollout scales down one stableRS pod, in order to make room for another canary

The fix is that when calculating the replica counts when scaling down the stableRS, it should consider the Spec.Replicas when it is higher than Status.AvailableReplicas.

This also adds many e2e tests to verify scaling behavior

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codecov-commenter commented Sep 27, 2020 •
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Codecov Report

Merging #739 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

Impacted file tree graph

@@           Coverage Diff           @@
##           master     #739   +/-   ##
=======================================
  Coverage   82.57%   82.57%           
=======================================
  Files          95       95           
  Lines        8012     8013    +1     
=======================================
+ Hits         6616     6617    +1     
  Misses        994      994           
  Partials      402      402
Impacted Files Coverage Δ
utils/replicaset/canary.go 78.04% <100.00%> (+0.13%) ⬆️

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@jessesuen jessesuen mentioned this pull request Sep 27, 2020
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jessesuen
jessesuen commented Sep 28, 2020
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utils/replicaset/canary.go
@@ -160,23 +160,23 @@ func CalculateReplicaCountsForCanary(rollout *v1alpha1.Rollout, newRS *appsv1.Re
}
}

minAvailableReplicaCount := rolloutSpecReplica - MaxUnavailable(rollout)
if GetReplicaCountForReplicaSets(oldRSs) > 0 {
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Note this was changed from GetAvailableReplicaCountForReplicaSets to GetReplicaCountForReplicaSets to avoid the same problem with older RSs.

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Also to simplify logic, i move the check to return early if there are older RSs up here, so all the logic below only has to deal with new and stable RS, and not have to factor in number of older RSs.

jessesuen
jessesuen commented Sep 28, 2020
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utils/replicaset/canary.go

if newRS != nil && *newRS.Spec.Replicas > desiredNewRSReplicaCount && scaleDownCount > 0 {
if newRS != nil && *newRS.Spec.Replicas > desiredNewRSReplicaCount {
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&& scaleDownCount > 0 check is/was unnecessary because replicasToScaleDown <= minAvailableReplicaCount covers that.

danny-stytch
danny-stytch approved these changes Sep 28, 2020
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I can't really comment on the e2e tests, but the actual code change LGMT.

khhirani
khhirani approved these changes Sep 28, 2020
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LGTM

dthomson25
dthomson25 approved these changes Sep 28, 2020
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What @danny-stytch said.

@jessesuen jessesuen merged commit b221be0 into argoproj:master Sep 28, 2020
jessesuen added a commit that referenced this pull request Sep 28, 2020
@jessesuen
fix: unavailable stable RS was not scaled down to make room for canary (
8239dd7 
#739)
This was referenced Oct 15, 2020
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@dthomson25 dthomson25 dthomson25 approved these changes

@khhirani khhirani khhirani approved these changes

@danny-stytch danny-stytch danny-stytch approved these changes

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