title: cron expression in AWS CloudWatch: How to run once a week
body: <p>In Amazon AWS CloudWatch it is possible to run a rule according to a schedule that is defined in a cron expression.</p>
  
  <p>The rules for this are outlined <a href="https://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/ScheduledEvents.html" rel="noreferrer">here</a>.</p>
  
  <p>After some trying around, I wasn't able to compose an expression that will run <strong>once a week</strong> (e.g. at 4 pm on Sunday). The following attempts were rejected by CloudWatch with the message <code>Parameter ScheduleExpression is not valid..</code>.</p>
  
  <pre><code>0 16 * * SUN *
  0 16 * * 6 *
  0 16 * * SUN-SUN *
  0 16 * * 6-6 *
  </code></pre>