XF 2.2 ECS Container not connecting to RDS database.

I'm launching a new site / forum, and thought this time around instead of using a EC2 instance I would try to containerize xenForo and run it through ECS.

My container is running locally and I have a fully functioning forum. And I have been able to get the ECS Task Definition to run Docker with the exact same config.

Only difference is I have set the environment variables to point to my RDS database, and not my local project.

I'm running into an issue which appears to me like the DB Host is not recognized.

The forum is showing the following error message:
An unexpected database error occurred. Please try again later.

And if you view the source / inspect you see the following comment:
<!-- php_network_getaddresses: getaddrinfo for fallback_host failed: Name or service not known -->

The ECS is on the same VPC as my RDS database. The correct security group is in place and the ECS Task Definition has "networkMode" set as "awsvpc" which should be correct for using AWS's internal DNS.

I have been stuck here for a few days, and not sure what else to try.

Was hoping someone here had any thoughts or has setup xenForo via Docker / ECS on AWS before and might be able to shed some light.
 
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