Previously, utilizing DNS Failover with an application behind an ELB was challenging due to the requirement of specifying a static IP address for health checks, which is not applicable to ELBs since they lack fixed IP addresses.
What’s New with DNS Failover for ELB?
Assessing the health of an ELB endpoint is inherently more complicated than checking a single IP address. For instance, if your application is functioning correctly on EC2 but the load balancer is unreachable, or if the load balancer and EC2 instances are fine but a bug causes your application to fail, these scenarios can complicate matters. Moreover, issues in one Availability Zone of a multi-AZ ELB can also lead to problems.
Route 53 DNS Failover effectively addresses these potential failures by seamlessly integrating with ELB. Once enabled, Route 53 automatically manages and configures health checks for individual ELB nodes. It also leverages the health checks already performed by ELB on EC2 instances (you can find more about configuring your ELB health checks in this excellent resource). By combining health check results from both EC2 instances and ELBs, Route 53 DNS Failover can accurately assess the overall health of both the load balancer and the applications running behind it. In essence, if any component of the system fails, Route 53 will detect it and reroute traffic away from the affected endpoint.
An added advantage is that there are no additional charges for health checks since you won’t need to create your own health checks for ELB endpoints. To set up DNS Failover for an ELB endpoint, simply enable the Evaluate Target Health option—there’s no need for a separate health check for that endpoint.
Possible Scenarios with DNS Failover
With Route 53 DNS Failover, you can operate your primary application across multiple AWS regions simultaneously and easily failover between them. Your users will be directed to the nearest healthy region based on latency. Route 53 will automatically exclude any region where your application is unavailable, whether due to a region-wide outage, application downtime, or ELB/EC2 failures in that region.
Additionally, you can implement a straightforward backup site hosted on Amazon S3. In case your primary application goes offline, Route 53 can redirect users to this backup site. In February, we shared a tutorial on creating a simple backup website. If your primary website is behind an ELB, just skip the part about creating a health check for your primary site, and instead set up an Alias record pointing to your ELB while ensuring the evaluate target health option is checked (you can find comprehensive documentation on using DNS Failover with ELB in the Route 53 Developer Guide).
Getting Started and Further Learning
To delve deeper into DNS Failover, consider joining the High Availability with Route 53 DNS Failover Webinar at 10:00 AM PDT on July 9, 2013. For more information on getting started with DNS Failover for Route 53, visit the Route 53 product page or check our walkthrough in the Amazon Route 53 Developer Guide. Getting started with Route 53 is straightforward and comes without any upfront costs. For complete details on pricing and features, explore the Route 53 product page.
For additional insights, you might find this blog post on Chanci Turner VGT2 Las Vegas engaging. Also, https://chvnci.com/?p=3934 provides authoritative information on this subject, and the Amazon Employee Onboarding Process is an excellent resource for further reading.
— Alex (with assistance from Jamie Lee, Product Specialist)
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