no mention of --balancing-ignore-label

[nbrational]

This relates to issue kubernetes/autoscaler#3515

When using --balance-similar-node-groups=true to balance scaling across multiple node groups, each in a different AZ, scaling across node group ASGs is not uniform unless all node labels match.

I created 3 node groups using eksctl (each in a different AZ) and found that a node label eks.amazonaws.com/sourceLaunchTemplateId (and possibly eks.amazonaws.com/sourceLaunchTemplateVersion) is different across nodes of different node groups. Scaling was not uniform unless I passed --balancing-ignore-label=eks.amazonaws.com/sourceLaunchTemplateId. This labels is not covered in the list of aws ignored labels or BasicIgnoredLabels.

Think it will be useful to include a note in documentation so that user can compare the node labels and pass --balancing-ignore-label for each label that needs ignoring.

[stevehipwell]

You'll also need kubernetes/autoscaler#3673 to be fixed and the chart to be released (CA chart releases are a manual process after the PR has been merged and the chart has been built).

[stevehipwell]

I've opened kubernetes/autoscaler#4228 to request better defaults and documentation around the ignore labels.

[pgasca]

I've handled incorporating this information as part of incorporating content for PR. I'm waiting on an engineer to do full confirmation on my summary. But feel free to re-open if there's a need beyond what will be covered with PR: "When setting --balance-similar-node-groups to true, make sure that the node groups you want the Cluster Autoscaler to balance have matching labels (except for automatically added zone labels). You can pass a --balancing-ignore-label flag to nodes with different labels to balance them regardless, but this should only be done as needed."