To fully understand our messaging infrastructure, we should also be looking at the SNS service. The CloudWatch overview console gives us a good glimpse into the operation of our SNS service. With the SNS, we will also be getting information about our messages rather than performance, but there are two crucial metrics to monitor when operating an SNS topic:

• Number of Notifications Delivered
• Number of Notifications Failed

These two metrics will help us get an overview of whether the topics are actually working and if the messages being published are being delivered or failed. In any scenario, there are bound to be failed messages, and we need to maintain a low number of failed messages versus a high number of delivered ones. Both of these metrics can be fed into a query result to create an alarm when the percentage of failed messages goes above a certain threshold. An overview console example is displayed in the following screenshot: