I am tasked with ensuring 99.99% availability for our global application. I need to understand the nuances of setting up a Global HTTP(S) Load Balancer with backends in both US-Central and Europe-West. How does GCP handle traffic steering if one region goes down, and what are the common pitfalls when syncing Cloud SQL databases across these disparate geographic locations to avoid latency?
3 answers
Achieving 99.99% availability is a significant undertaking. GCP’s Global Load Balancer is unique because it uses a single anycast IP address, automatically routing users to the closest healthy backend. For the database layer, you should use Cloud SQL Cross-Region Replicas. In the event of a regional failure, you must manually promote the replica to a standalone instance, as automatic failover across regions is not a native feature like it is for multi-zone setups. We successfully tested this by simulating a region outage, and our traffic redirected within seconds, though the DB promotion took a few minutes.
Have you looked into using Cloud Armor in front of that load balancer to prevent DDoS attacks from triggering a "failover" that isn't actually needed due to traffic spikes?
The biggest pitfall is data consistency. Remember that cross-region replication is asynchronous, so there is always a slight RPO (Recovery Point Objective) lag you must account for.
Exactly, Melissa. Testing your RTO and RPO regularly is the only way to be sure that your 99.99% target is actually achievable during a real-world regional disaster.
Brian, that is a sophisticated point. Without Cloud Armor, a botnet could saturate one region, making it appear "unhealthy" to the load balancer's health checks. By filtering traffic at the edge, you ensure that the failover logic only triggers for actual infrastructure issues rather than malicious traffic surges. It’s an essential layer for any global deployment.