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I currently have an AWS load balancer and it has a target group, containing an instance per AZ: 2 of these are unhealthy and I have configured the attributes of the target group so DNS failover requires at least 2 healthy targets. I now get an error triangle but am not sure what change I am meant to see? Should it remove the load balancer A record for an AZ? How does it actually work? If an AZ went down when would traffic stop being sent there?

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AWS does not directly offer DNS failover for individual instances within a target group associated with a load balancer. However, AWS does provide health checks and the ability to route traffic conditionally based on the health of targets within a target group. Here's how it generally works:

  • Health Checks: Load balancers only send traffic to healthy instances, as determined by health checks.

  • Routing Traffic: Traffic is not routed to instances that fail health checks.

  • DNS Failover: Handled by Route 53, not the load balancer. Route 53 can reroute traffic based on health check results.

  • Error Indicator: The error triangle in the AWS Console indicates a health check failure. It does not directly affect DNS.

  • Target Group Attributes: If healthy instances fall below the configured threshold, the load balancer may stop routing traffic to all instances in the target group.

  • Load Balancer A Record: The A record remains pointed at the load balancer. It does not change with instance health.

  • Availability Zone Outage: Traffic is automatically rerouted away from an unavailable AZ to other healthy AZs.

If your target group falls below the required number of healthy instances, the load balancer will stop routing traffic to the entire group. DNS changes occur only if configured in Route 53.

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