Accept InstanceDistribution with only one instance type.

[ryotarai]

Description

Currently, InstanceDistribution must have more than or equal to 2 instance types but AWS auto scaling API accepts configuration with only one instance type too. This PR makes InstanceDistribution accept that case.

Q. Why we do not use just instanceType of nodegroup?

We want to launch spot instances with one instance type.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, and examples directory)
• Manually tested
  • To run tests, Remove impossible condition: nil != nil #1771 is needed
• Added labels for change area (e.g. area/nodegroup) and target version (e.g. version/0.12.0)
• Added note in docs/release_notes/draft.md (or relevant release note)

[ryotarai]

@martina-if Hi, would you please review this PR?

[martina-if]

Hi @ryotarai , last time I checked this wasn't supported with MixedInstances, do you have a link to some docs where it says now this is supported? (it was supported through another mechanism though https://github.com/weaveworks/eksctl/pull/781/files)

[ryotarai]

Thank you for reviewing.

last time I checked this wasn't supported with MixedInstances, do you have a link to some docs where it says now this is supported?

https://docs.aws.amazon.com/autoscaling/ec2/APIReference/API_LaunchTemplate.html
(MixedInstancesPolicy.LaunchTemplate of CreateAutoScalingGroup request)

This page says You can specify between 1 and 20 instance types. and the following config worked in my environment.

  instancesDistribution:
    instanceTypes: ["c5.large"]
    spotInstancePools: 1
    onDemandBaseCapacity: 0
    onDemandPercentageAboveBaseCapacity: 0

it was supported through another mechanism though https://github.com/weaveworks/eksctl/pull/781/files

I didn't notice that. Thank you.
However, to set onDemandBaseCapacity, we need instancesDistribution.

[martina-if]

This is great! Apparently they changed that in October.

Ok, two tiny details to complete the PR:

• https://github.com/weaveworks/eksctl/blob/master/examples/08-spot-instances.yaml#L16
• https://github.com/weaveworks/eksctl/blob/master/site/content/usage/08-spot-instances.md

Can you please fix the comment in those two files^? It says minimum 2 instance types. Then if you rebase I'll approve and merge it :)

Thanks a lot!

[ryotarai]

I've updated the example and doc and rebased this to master branch: 5d9436d
(Should I squash commits into one commit?)

[martina-if]

Hi @ryotarai , yes it would be great if you could squash them :)

[ryotarai]

I've squashed commits into 2cc4936

[martina-if]

Thank you @ryotarai !