Cannot load anything other than root request -- ECS + ECR + ALB 503s

Question

Greetings,  
  
I have a simple static site behind NGINX in a container. I have pushed the image to ECR, and can pull and run the container without any issues.  
  
However, when I put an Application Load Balancer in front of the ECS Service with Fargate, I am unable to load any assets. For that matter, anything beyond the root does not load: i.e. subdomain.example.com loads, and subdomain.example.com/* throws a 503.  
  
As mentioned, I can run the container locally without issue by pulling the :latest tag, so I am confident it's not an issue with the container, and the issue lies somewhere in the configuration of the ALB and ECS Service.  
  
Any guidance would be greatly appreciated.

Answer

This turned out to be a misconfigured Listener that was pointed at an incorrect target group. I don't see any way to delete my question, so I figured I'd share the "solution."

Cannot load anything other than root request -- ECS + ECR + ALB 503s

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