Untitled

  # elasticache
  ElastiCacheCluster:
    Type: 'AWS::ElastiCache::CacheCluster'
    Properties:    
      CacheSubnetGroupName: !Ref ElastiCacheSubnetGroup # was missing <------
      Engine: memcached
      CacheNodeType: cache.t2.micro
      NumCacheNodes: 1
      VpcSecurityGroupIds: 
        - !Ref ElasticacheSecurityGroup

  ElastiCacheSubnetGroup:
    Type: 'AWS::ElastiCache::SubnetGroup'
    Properties:
      Description: "Subnet group for WP ElastiCache"
      SubnetIds:
        - !Ref DataSubnetA
        - !Ref DataSubnetB