Network Firewall firewall is deployed across multiple AZs

# Terraform: Add a second subnet_mapping to deploy the firewall across multiple AZs
resource "aws_networkfirewall_firewall" "<example_resource_name>" {
  name                = "<example_resource_name>"
  firewall_policy_arn = "<example_firewall_policy_arn>"
  vpc_id              = "<example_vpc_id>"

  subnet_mapping {
    subnet_id = "<subnet-id-1>"
  }

  subnet_mapping {
    subnet_id = "<subnet-id-2>"  # CRITICAL: second subnet in a different AZ for multi-AZ
  }
}

# CloudFormation: Ensure the firewall spans multiple AZs by adding a second subnet mapping
Resources:
  <example_resource_name>:
    Type: AWS::NetworkFirewall::Firewall
    Properties:
      FirewallName: <example_resource_name>
      FirewallPolicyArn: <example_firewall_policy_arn>
      VpcId: <example_vpc_id>
      SubnetMappings:
        - SubnetId: <subnet-id-1>
        - SubnetId: <subnet-id-2>  # CRITICAL: second subnet in a different AZ to achieve multi-AZ