AWS: only cache instance requirements when needed

[rrangith]

What type of PR is this?

/kind bug
/kind regression

Fixes #7102

What this PR does / why we need it:

This PR reduces the number of unneeded DescribeLaunchTemplateVersions API calls. Previously there was a PR that only looked for instance requirements when needed #5550. However this PR #6245 introduced a regression where now it looks for instance requirements all the time.

However in the original fix PR it was stated:

But retrieving InstanceRequirements should only be useful when the LT overrides don't already specify an InstanceType, as both are mutually exclusive. The api reference doc states:

If you specify InstanceRequirements, you can't specify InstanceType.

That mutual exclusion is already leveraged by getInstanceTypesForAsgs: we don't look for InstanceRequirements when we have a mixed instance policy specifying instance types overrides.

This PR makes it so we again only look for instance requirements if instance type overrides are not used.

The screenshot below shows the huge increase in DescribeLaunchTemplateVersions API calls when we upgraded our cluster autoscaler to include the bug PR at 16:00 #6245

The screenshot below is after I applied this fix at 10:30, and the DescribeLaunchTemplateVersions API calls dropped back down.

The screenshot below shows the main loop duration spiking when the bug was introduced after 15:00 and the duration returned to normal after my fix at 10:30

Does this PR introduce a user-facing change?

AWS: Only cache instance requirements when needed

[k8s-ci-robot]

Hi @rrangith. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[adrianmoisey]

/ok-to-test

[gjtempleton]

/assign @gjtempleton

[gjtempleton]

Thanks for this
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gjtempleton, rrangith

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• cluster-autoscaler/cloudprovider/aws/OWNERS [gjtempleton]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment