Enable spot instance draining when it's required

[Lawstorant]

what

instance_market_options are optional and not needed to launch spot instances. Current behavior can lead to sudden breaks in service and uncontrolled loss of capacity.

why

Using this module, one can create spot capacity but without the proper draining management. Fixing this will lead to more stable service when market options are not defined (because they don't have to be). There aren't any requirements to enable this setting though still omitting it with pure on-demand capacity providers doesn't hurt.

references

(this has already happened to me in testing environment)
#18
https://docs.aws.amazon.com/AmazonECS/latest/developerguide/managed-instance-draining.html

[Gowiem]

/terratest

[jamengual]

Mmm, I think we are trying to apply logic to something that might not be entirely related to the intent of spot draining.
maybe we can add to var.capacity_providers_ec2 a enable_spot_instance_draining = optional(bool, false) instead?

[Lawstorant]

Honestly, I don't see a reason why anybody would NOT want this option if using spot instances.

If we went the variable route, my only suggestion (from experience) would be to make it enabled by default. It just doesn't really make sense not to properly drain tasks from an instance that will be yanked in two minutes.