Terraform RDS database credentials

Question

I am trying to use AWS secrets manager to declare RDS admin credentials.

1. Declared credentials in rds.tf in variable RdsAdminCred as key/value pair
2. Declared secret as well in the same tf file

variable "RdsAminCred" {
    default = {
        username = "dbadmin"
        password = "dbadmin#02avia"
    }
    type = map(string)
}

resource "aws_secretsmanager_secret" "RdsAminCred" {
  name = "RdsAminCred"
}
resource "aws_secretsmanager_secret_version" "RdsAminCred" {
  secret_id     = aws_secretsmanager_secret.RdsAminCred.id
  secret_string = jsonencode(var.RdsAminCred)
}

3. I am not sure how to use the secret string in the declaration below, to replace the hardcoded value for username and password.

resource "aws_db_instance" "default" {
  identifier            = "testdb"
  allocated_storage    = 20
  storage_type         = "gp2"
  engine               = "mysql"
  engine_version       = "5.7"
  instance_class       = "db.t2.medium"
  name                 = "mydb"
 
  username             = "dbadmin"
  password             = "dbadmin#01avia"

Any help is appreciated..

Answer 1

I'd recommend using the random_password resource instead. Then you can reference that in the cluster configuration and secrets manager.

Example:

resource "random_password" "master_password" {
  length  = 16
  special = false
}

resource "aws_rds_cluster" "default" {
  cluster_identifier = "my-cluster"
  
  master_username = "admin"
  master_password = random_password.default_master_password.result

  # other configurations
  # .
  # .
  # .
}

resource "aws_secretsmanager_secret" "rds_credentials" {
  name = "credentials"
}

resource "aws_secretsmanager_secret_version" "rds_credentials" {
  secret_id     = aws_secretsmanager_secret.rds_credentials.id
  secret_string = <<EOF
{
  "username": "${aws_rds_cluster.default.master_username}",
  "password": "${random_password.master_password.result}",
  "engine": "mysql",
  "host": "${aws_rds_cluster.default.endpoint}",
  "port": ${aws_rds_cluster.default.port},
  "dbClusterIdentifier": "${aws_rds_cluster.default.cluster_identifier}"
}
EOF
}