[Bug] placement group should be optional for capacity reservations

[vsoch]

When we create a cluster with a capacity reservation (e.g., with GPUs) it's often the case that EFA comes with the set. However, setting a placement group can actually limit the instances you get in the reservation. We had a reservation for 16, but because eksctl sneakily added a default placement group, we only were able to get 11. I was unable to set the groupName to null and had to comment out this block

eksctl/pkg/cfn/builder/managed_launch_template.go

Lines 80 to 87 in fc24e94

	if mng.Placement == nil {
	groupName := m.newResource("NodeGroupPlacementGroup", &gfnec2.PlacementGroup{
	Strategy: gfnt.NewString("cluster"),
	})
	launchTemplateData.Placement = &gfnec2.LaunchTemplate_Placement{
	GroupName: groupName,
	}
	}

with a custom build of eksctl to create our cluster with a full 16. My suggestion would be to either add an explicit flag that says "don't make a placement group with efa" or allow the user to create a cluster with efa, but give red warnings about needing the group.

Thanks for fixing this - ping @bollig and @milroy to stay in the loop, this is the issue we faced yesterday / today (which is fixed now with our custom build).

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[vsoch]

Please don't go stale! Others could definitely run into this issue.