DNS caching

Unless you use a smart database driver, you depend on DNS record updates and DNS propagation for failovers, instance scaling, and load balancing across Aurora Replicas. Currently, Aurora DNS zones use a short Time-To-Live (TTL) of five seconds. Ensure that your network and client configurations don’t further increase the DNS cache TTL.

Remember that DNS caching can occur anywhere from your network layer, through the operating system, to the application container. For example, Java virtual machines (JVMs) are notorious for caching DNS indefinitely unless configured otherwise. Here are some examples of issues that can occur if you don’t follow DNS caching best practices:

• After a new primary instance is promoted during a failover, applications continue to send write traffic to the old instance. Data-modifying statements will fail because that instance is no longer the primary instance.

• After a DB instance is scaled up or down, applications are unable to connect to it. Due to DNS caching, applications continue to use the old IP address of that instance, which is no longer valid.

• Aurora Replicas can experience unequal utilization, for example, one DB instance receiving significantly more traffic than the others.