Why did AWS Global Accelerator fail over to an endpoint in a different Region?

Resolution

Global Accelerator uses traffic dial settings to route traffic to endpoint groups. To determine the proportion of traffic that's directed to an endpoint, Global Accelerator uses endpoint weight. If there's no healthy endpoint with a weight greater than 0, then Global Accelerator fails over to a healthy endpoint in another endpoint group.

To prevent Global Accelerator's failover to a different endpoint group, check the traffic dial settings and the endpoint weights in the endpoint groups. Then, verify the health of the endpoints. If the endpoints don't pass a health check, then see Why is AWS Global Accelerator failing health checks with endpoints?

Example: You configure Global Accelerator with three endpoint groups, and set the following traffic dial settings:

EndpointGroup 1: Dial 100

EndpointGroup 2: Dial 0

EndpointGroup 3: Dial 0

If EndpointGroup 1 doesn't have healthy endpoints with a weight greater than 0, then Global Accelerator checks up to two additional endpoint groups. If endpoint groups 2 and 3 are closest to the client and are healthy with a weight greater than 0, then the accelerator fails over. The accelerator ignores the traffic dial settings and routes traffic to the endpoint in these endpoint groups.

An endpoint with 0 weight doesn't receive any traffic, even if the endpoint is healthy. If all the endpoints have 0 weight, then the accelerator tries to find endpoints with a weight greater than 0 in another endpoint group. If the accelerator locates a healthy endpoint with a weight greater than 0, then the accelerator routes traffic to that endpoint. If the accelerator doesn't locate a healthy endpoint, then the accelerator fails over and includes endpoints in the nearest endpoint group.

Example: You configure instance 1 as an endpoint in EndpointGroup 1 and instance 2 as an endpoint in EndpointGroup 2. If the weight of instance 1 is 0, then the accelerator fails over. If instance 2 is healthy and has a weight greater than 0, then Global Accelerator routes traffic to instance 2.

Related information

Deploying multi-Region applications in AWS using AWS Global Accelerator

Traffic management with AWS Global Accelerator