ELB health check fail AWS

Question

My ELB health check fails all the time but cannot figure it why (502 bad gateway).

I have a cluster (ECS) with a service that runs at least one task (Fargate) which is a Node API listening on port 3000 & 3001 (3000 for http & 3001 for https since I cannot use port below 1024).

I have an Elastic Load Balancer (application) that is listening on port 80. It forwards the trafic on a target group with protocol port 3000.

This target group has as target type: ip address since I use fargate and not EC2 for my tasks. So when a task is turning on, I correctly see the private IP of the task registering into the target group.

My health route is server_ip_address/health and it returns a classic 200 status code. This route works well because I tried it directly from the public ip address of the task (quickly before it stopped because of the health check failing) and it returns a 200. I also tried it through the ELB dns name (so my-elb.eu-west-1.elb.amazonaws.com/health) and it worked well as well so I don't understand why the health check fail.

Anyone know what I missed?

Answer 1

In the screenshot of your targets in the target group it is showing the port as 80, this means that the load balancer (and health check) will be attempting to connect to the Fargate container on port 80.

You mentioned that it should be served from port 3000, therefore you will need to ensure that the target group is listening on port 3000 instead. Once this is in place, assuming that the security group of the host allows inbound access the 502 error should go away.

To be clear the listener port is what port the client connects to, whereas the target port is the port the load balancer connects to your target on.