Simulate AZ failure in ECS Fargate cluster with Application Load Balancer
I have a ECS cluster running Fargate profile and ECS service associated to public ALB (2 AZs), running one task. I´m trying to simulate an AZ failure blocking all traffic in one AZ using Network ACL.
As expected, the application fails but the ALB target group health check keeps "healthy" status, I´d expect the health check to fail and start another ECS task in a different subnet. Am I missing something here? Thanks a lot
ECS Service Health status with all subnet traffic blocked by NAC
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Update: trying to block subnet traffic using NACL in this scenario is not recommended because the ALB deploys ENIs directly to the subnets and the health check traffic ends up not passing through the NACL. The ideal in this case is to block using SGRP and that worked fine. After SGRP "not allowing rules", the ALB health check failed as expected. Thank you
Is there an ALB interface and ECS task on the same Subnet where your trying to block the traffic? If so, the Health check on the Same AZ will succeed because the ACL will not block the traffic and you may be connecting to ALB via a different AZ thus getting the 504
It only has to pass one health check to be considered healthy
I´m testing using one task, all subnet traffic is blocked by NACL, application is failing (as expected) but ALB status keeps as "healthy". I´ve tested with several subnets and got same behaviour: no health check failures, thank you
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Just what I said. The ecs task is in the same subnet as your alb.