AWS - Target Group Load Balancer - amazon-web-services

Question

I have a load balancer and an Nginx that sits behind the LB.
Below is the nginx config.
upstream app {
server service_discovery_name.local:5005;
}
server { // Reverse proxy for VPC ES to be available on public
listen 80;
location / {
proxy_pass vpc-es-domain-url;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
server { // reverse proxy for django app
listen 8005;
location / {
proxy_pass http://app;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_redirect off;
}
}
I've a listener attached to the ALB, listening at port 80, that forwards the traffic to the target IP. The target group has the private IP of the Nginx container. I use Fargate-ECS container.
Now when I route to ALB_url:80, it opens up the elasticsearch. However, when I route to ALB_url:8005, it fails to load anything. The django_app is running at port 5005, check by explicitly browsing to the IP=:5005.
I believe the nginx config is right. I want my traffic to be routed via ALB -> Nginx -> apps. What exactly am I missing?

Answer 1

When you configure an ALB you must create a listener, specify the port and the action(forward the request to Target Group or make redirects), you can create a multiples listener using different ports, for example, you can have a listener listening in 80 port and doing redirects to HTTPs and another listener with 443 port forwarding the request to Target Group.
According to that, I understand that your configuration is:
- ALB listening in 80 port and sending the request to Target Group.
- Target Group listening in 80 port and sending the request to Fargate Task(nginx server)
When you route to ALB_URL:80 the request is forwarded to Target Group by 80 port and the request is sending to Fargate task. But when you route to ALB_URL:8005 that will no work because the ALB doesn't have a listener for that port.
You can create a listener with 8005 port that forwards the request to a Target Group listening in the 8005. with this configuration when you route ALB_url:8005 the request will be sent to TG created and then will send to the Fargate task and will take the configuration into the Nginx config.
ALB---> listener 80 ----> Target Groupt port 80 ----> ECS Task Nginx
ALB---> listener 8005 ---> Target Groupt port 8005 ----> ECS Task Nginx
Don't forget to validate the Security groups to allow 8005 port
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#target-group-routing-configuration