Problem with connecting frontend and backend services through internal load balancer

Question

I'm new to deploying web applications on AWS, but my co-workers are unable to solve the problem so if anyone can help with our problem, it'd be great.

Frontend and backend service seem to be working fine separately on its own, but when I try to communicate between frontend and backend I keep getting ERR_NAME_NOT_RESOLVED error.

• Service discovery are all connected
• All security groups are open

my AWS architecture

I think our architecture is very similar to this if that helps. (https://mohamedwaelbenismail.medium.com/microservices-architecture-deployed-on-ecs-fargate-based-cluster-using-cloudformation-878cb6f90571)

• It only works if we change the internal load balancer to public load balancer allow internet traffic and allow 0.0.0.0/0.
• Status of health check are all 'healthy'

Answer 1

It sounds like the communication between the frontend and backend services is being blocked by the internal load balancer. Here are a few things you can check to troubleshoot the issue:

1. Check the DNS settings: The ERR_NAME_NOT_RESOLVED error could indicate that the frontend service is unable to resolve the DNS name of the backend service. Make sure that the DNS settings are correct and that the frontend service is configured to use the DNS name of the backend service.

2. Check the security group rules: Even though you mentioned that the security groups are open, double-check to make sure that the security group rules are configured to allow traffic between the frontend and backend services. You should also make sure that the security group associated with the internal load balancer is allowing traffic from both the frontend and backend services.

3. Check the routing configuration: Make sure that the routing configuration for the internal load balancer is set up correctly to route traffic between the frontend and backend services. Check that the target groups associated with the frontend and backend services are correctly associated with the load balancer.

4. Check the logs: Check the logs of both the frontend and backend services to see if there are any error messages or other information that could help diagnose the issue.

5. Test the communication between the services: Use tools like curl or telnet to test the communication between the frontend and backend services directly. This can help you isolate where the issue is occurring.

Hopefully, one of these suggestions will help you resolve the issue.

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