Create a Cloud Armor security policy, and associate the policy with the load balancer. Configure the security policy's settings as follows: action: throttle; conform action: allow; exceed action: deny-429.

Configure the load balancer to accept only the defined amount of requests per client IP address, increase the backend servers to support more traffic, and redirect traffic to a different backend to burst traffic.

Create a Cloud Armor security policy, and apply the predefined Open Worldwide Security Application Project (OWASP) rules to automatically implement the rate limit per client IP address.

Configure a VM with Linux, implement the rate limit through iptables, and use a firewall rule to send an HTTP 429 response to the client application.