AWS Cloud Architecture•Part 2: Networking, VPC & Traffic Routing (6 - 20)
ALB target health checks and Connection Draining (Deregistration Delay).
In Simple Words: When an EC2 or container is de-registered or updated, connection draining keeps active in-flight requests alive for a configured time (e.g., 300 seconds) while stopping new requests from reaching it. This guarantees zero dropped requests during rolling deployments.
hcl
resource "aws_lb_target_group" "app_tg" {
name = "app-target-group"
port = 80
protocol = "HTTP"
vpc_id = aws_vpc.main.id
deregistration_delay = 30 # Connection draining timeout in seconds
health_check {
path = "/health"
healthy_threshold = 2
unhealthy_threshold = 3
timeout = 5
interval = 15
}
}