Cfn-python-lint: Validate UpdatePolicy for AutoScalingRollingUpdate

[adamchainz]

cfn-lint version: (cfn-lint --version) 0.7.2

Description of issue.

Using a template like:

Resources:
  AutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      # ...
      MinSize: "1"
      MaxSize: "1"
      # ...
    UpdatePolicy:
      AutoScalingRollingUpdate:
        MinInstancesInService: 1

will fail at deployment time with an error from CloudFormation like:

AWS::AutoScaling::AutoScalingGroup AutoScalingGroup UPDATE_FAILED: MinInstancesInService must be less than the autoscaling group's MaxSize

It would be nice to have protection against this. I guess there are other constraints, some are in the docs. I submitted a docs PR for this one.

[cmmeyer]

Agreed. This would be a good business logic addition to compare values. I'll label this as an enhancement.

[kddejong]

Started with rule E3016 to check the basic configuration of the UpdatePolicy (attributes, values are of the correct type), etc.

Moving down the chain to this one next.

[kalpik]

I have an issue with UpdatePolicy validation. I am using a different update policy for spot instances (replacingupdate) and regular instances (rolling update)

So something like:

UpdatePolicy:
            !If
                - spotInstances
                - AutoScalingReplacingUpdate:
                      WillReplace: true
                - AutoScalingRollingUpdate:
                      MinInstancesInService: !Ref DedicatedIngestNodeCount
                      MinSuccessfulInstancesPercent: 100
                      MaxBatchSize: 1
                      PauseTime: PT15M
                      WaitOnResourceSignals: true
                      SuspendProcesses:
                          - HealthCheck
                          - ReplaceUnhealthy
                          - AZRebalance
                          - AlarmNotification
                          - ScheduledActions

But this gives the following linting error:

E3016 UpdatePolicy doesn't support type Fn::If

This code actually works in CFN, so can the linting be fixed for this?

Thanks!

[kddejong]

Sorry @kalpik I lost track of this. I have created pull request #468 totally rewritten to handle conditions on each level. Used your example for adding to tests. Thanks for reporting this.

[digash]

I am getting error E3016 UpdatePolicy doesn't support type AutoScalingRollingUpdate from this AWS example:
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/quickref-autoscaling.html#scenario-as-updatepolicy