The hidden weakness of AWS Global Accelerator.

AWS Global Accelerator (GA) is a service that routes incoming traffic to healthy targets across multiple AWS regions. It provides a single entry point for global traffic, which is then distributed to the optimal target endpoint based on health checks and traffic routing policies. The problem with the GA's health checking process is that it only inherits the health status of the target, such as Application Load Balancer (ALB), Elastic Load Balancer (ELB), or EC2 instances, instead of performing its own health check.

As a result, if there are any network or security issues that prevent traffic from reaching the target listener, the GA will not be able to detect this, and will continue to send traffic there, potentially causing downtime and poor user experience. For example, if a security group rule blocks incoming traffic from the GA to the target, or if a routing issue prevents traffic from reaching the target, the GA will not know about it, and will consider the target to be healthy, even though the target is not accessible.

To work around this issue, it is important to implement additional health checks that specifically test the connectivity and accessibility of the target from the GA. One approach is to use a health checker tool, such as Amazon CloudWatch Synthetics, to perform a custom health check on the target. CloudWatch Synthetics can simulate a user's request to the target and verify that the target is responding correctly. If the target fails the custom health check, CloudWatch Synthetics can mark the target as unhealthy, and the GA will stop sending traffic to it.

It is also important to monitor the network and security configuration of the GA and the target to ensure that traffic can flow freely between them. This can be achieved by monitoring the network logs, such as AWS VPC Flow Logs, and security logs, such as AWS CloudTrail logs, to detect any potential issues that may block incoming traffic.

In conclusion, the problem with the Global Accelerator health check is a serious issue that can result in poor performance, slow response times, and dropped connections. To work around this problem, it is important to properly configure the security groups and ACLs for the target listeners, to configure the health checks for the target listeners, and to closely monitor any security or routing changes that affect the target listeners. By taking these steps, you can ensure that the Global Accelerator is functioning optimally, and that your applications are delivering the best possible performance for your users.