title: AWS SNS not registering successfully executed action from AWS Cloudwatch
body: <p>I have created AWS Cloudwatch Alarm on a Target group for my Elastic Load Balancer.</p>
  
  <p>Once the alarm state goes from OK to Alarm it is should send notification to an AWS SNS Topic with a Lambda function as subscriber.</p>
  
  <p>What I have tested:</p>
  
  <ul>
  <li>The lambda function works with a dummy SNS event</li>
  <li>Publishing a test message to the SNS Topic results in all subscribers being notified</li>
  <li>The CloudWatch Alarm successfully goes into state Alarm.</li>
  <li>The CloudWatch Alarm History says "2019-08-04 13:18:00   Action  Successfully executed action arn:arn:aws:sns:eu-west-1:something"</li>
  </ul>
  
  <p>It seems like there is something wrong in the link between the CloudWatch Alarm and the SNS Topic. The SNS topic Access Policy has been configured to "Everyone" and still no luck.</p>
  
  <p>The exact settings on my CloudWatch Alarm</p>
  
  <pre><code>Threshold
  UnHealthyHostCount &gt; 0 for 1 datapoints within 1 minute
  
  ARN
  arn:aws:cloudwatch:eu-west-1:xxxxx:alarm:awsapplicationelb-targetgroup-API-Workers-xxxxxx-High-Unhealthy-Hosts
  
  Namespace
  AWS/ApplicationELB
  
  Metric name
  UnHealthyHostCount
  
  LoadBalancer
  app/Backend-API-HTTPS/xxxxxx
  
  TargetGroup
  targetgroup/API-Workers/xxxxx
  
  Statistic
  Sum
  
  Period
  1 minute
  
  Datapoints to alarm
  1 out of 1
  
  Missing data treatment
  Treat missing data as bad (breaching threshold)
  
  Percentiles with low samples
  evaluate
  </code></pre>
  
  <p>The actions configured for this were selected from a list of "Select an existing SNS topic". I also tried configuring the topic ARN directly. In both cases the configuration of the actions are marked as <code>valid</code> by the AWS console.</p>