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Redis – Fn::Equals throwing error when CommaDelimitedList parameter is used

I am writing a CF template to create an Elasticache Replication group. In that, I have a parameter called Snapshots of CommaDelimitedList type, which is used to pass RDB snapshot files stored in s3 as a list of ARNs –

Snapshots:
    Description: >-
      List of ARNs of Redis RDB snapshot files to populate the Elasticache
      cluster (optional)
    Type: CommaDelimitedList

I’m trying to have a Condition like below, which is going to check if Snapshots is empty or not –

Conditions:
  HasSnapshots: !Not 
    - !Equals 
      - !Ref Snapshots
      - ''

When I try to validate my template in CloudFormation Designer, it throws an error –

29/07/2020, 22:50:33 - Template contains errors.: Template error: every Fn::Equals object requires a list of 2 string parameters.

What would be the correct way to do this? Do I have to use String type for Snapshots instead of CommaDelimitedList? Or any other better approach?

I need this parameter for a Resource of type AWS::ElastiCache::ReplicationGroup as shown below, to populate the ElastiCache cluster with snapshot files given as a list of ARNs in Snapshots parameter, if provided so –

RedisReplicationGroup:
  Type: 'AWS::ElastiCache::ReplicationGroup'
  Properties:
    ...
    ...
    SnapshotArns: !If 
      - HasSnapshots
      - !Ref Snapshots
      - !Ref 'AWS::NoValue'
Tags:

2

Answers


  1. 0

    You can do the following using Join:

    Conditions:

  HasSnapshots: !Not 
    - !Equals 
      - !Join ["", !Ref Snapshots]
      - ''
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  2. 0

    Not sure if you were able to figure this out, but this might work

    !Not [!Equals [!Ref Snapshots, '']]
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