Pseudocode for Security Group User Pattern

security-group-pattern.tf

resource "aws_rds_cluster" "db" {
    ...
    security_group = ""
    ...
}

resource "aws_security_group" "airflow-db" {
    ...
}

resource "aws_security_group" "airflow-db-user {
    ...
}

resource "aws_security_group_rule" "db-user" {
    security_group = aws_security_group.airflow-db
    source_security_group = aws_security_group.airflow_db_user
    port = 5432
}

resource "aws_ecs_service" "api" {
    ...
    security_groups = [ 
        aws_security_group.airflow_db_user.id,
        ...
        ...
    ]
    ...
}

This was super helpful. I think I successfully implemented this paradigm in just-city/jc-pipeline-cluster-terraform repo in security_groups.tf if you want to check it out.