A company runs an application behind Application Load Balancers in two AWS Regions and wants clients to fail over to the healthy Region within seconds of an outage, without depending on DNS TTL expiry or client-side DNS caching to pick up a change. Which AWS service is purpose-built for this, and how does it avoid the DNS-caching delay?
- AWS Global Accelerator, because it gives the application a small set of static anycast IP addresses that clients connect to directly; Global Accelerator then routes each connection to a healthy endpoint over the AWS global network, so failover doesn't depend on clients re-resolving DNS at all
- Amazon Route 53 with a simple routing policy, because Route 53 always propagates DNS record changes to every resolver worldwide within one second regardless of the record's configured TTL
- AWS Global Accelerator, because it works by rewriting the DNS response's TTL to zero, forcing every client and resolver to bypass caching entirely
- Amazon CloudFront, because CloudFront edge locations independently re-run health checks against the origin and silently update the client's own cached DNS records without any client action needed
Why A? And why not the others?
Correct answer: A. AWS Global Accelerator, because it gives the application a small set of static anycast IP addresses that clients connect to directly; Global Accelerator then routes each connection to a healthy endpoint over the AWS global network, so failover doesn't depend on clients re-resolving DNS at all
AWS Global Accelerator provides an application with a small, fixed set of static anycast IP addresses that clients connect to directly; because clients target these unchanging IP addresses rather than a hostname whose DNS record has to be re-resolved, Global Accelerator can continuously health-check the regional endpoints and redirect traffic at the network routing layer, giving failover in seconds without ever requiring a client or resolver to notice a DNS change. The Route 53 option is wrong because DNS-based failover fundamentally depends on resolvers eventually re-querying and respecting the record's TTL, and real-world resolver and client-side caching frequently ignores or overshoots configured TTLs, which is precisely the delay Global Accelerator is designed to avoid. The 'rewrites TTL to zero' option is wrong because Global Accelerator's failover mechanism isn't a DNS trick at all; it works by routing already-established anycast IP traffic to a different backend, with no DNS response or TTL involved. The CloudFront option is wrong because CloudFront is a content delivery network for caching and accelerating content delivery from origins, not a mechanism for sub-DNS-TTL regional failover of an application's compute endpoints.
Source: AWS Global Accelerator Developer Guide: How AWS Global Accelerator works — static anycast IP addresses as fixed entry points, continuous health checks, and instant redirection to healthy endpoints without DNS involvement.