feat: support scaleDownDelaySeconds in canary w/ traffic routing

[jessesuen]

Resolves #478

This change introduces scaleDownDelaySeconds and scaleDownDelayRevisionLimit to the canary strategy when used with traffic routing:

  strategy:
    canary:
      scaleDownDelaySeconds: 30        # default 30s
      scaleDownDelayRevisionLimit: 1
      trafficRouting:
...

The purpose of a scaleDownDelaySeconds for canary with traffic routing, is the same reason for blue-green scaleDownDelaySeconds. We want to avoid scaling down the stable stack prematurely in order to give some time for service selectors to propagate to mesh providers and ingress controllers, and avoid 500 errors. This change will introduce a default 30s delay before scaling down stable stack just like in blue-green.

[codecov]

Codecov Report

Merging #1056 (506a6af) into master (1fa63d7) will decrease coverage by 0.00%.
The diff coverage is 82.58%.

@@            Coverage Diff             @@
##           master    #1056      +/-   ##
==========================================
- Coverage   81.24%   81.23%   -0.01%     
==========================================
  Files         103      103              
  Lines        9192     9243      +51     
==========================================
+ Hits         7468     7509      +41     
- Misses       1229     1233       +4     
- Partials      495      501       +6     

Impacted Files	Coverage Δ
rollout/replicaset.go	63.33% <71.42%> (+3.63%)	⬆️
rollout/canary.go	78.87% <74.07%> (-4.61%)	⬇️
rollout/bluegreen.go	70.91% <85.18%> (+0.35%)	⬆️
utils/defaults/defaults.go	87.03% <88.88%> (-0.72%)	⬇️
rollout/sync.go	74.78% <90.47%> (+2.41%)	⬆️
pkg/apis/rollouts/validation/validation.go	90.25% <100.00%> (+0.12%)	⬆️
pkg/kubectl-argo-rollouts/info/rollout_info.go	79.04% <100.00%> (+0.12%)	⬆️
rollout/trafficrouting/istio/istio.go	79.91% <100.00%> (+0.26%)	⬆️
utils/replicaset/replicaset.go	89.70% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1fa63d7...506a6af. Read the comment docs.

[khhirani]

LGTM

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
2 Code Smells

No Coverage information
2.6% Duplication