GCP - Application Load Balancing

            
 

            

        

          

          

              

                  
              

          










    
This guide provides a beginner-friendly walkthrough for setting up a Global External Application Load Balancer (HTTP/HTTPS) on Google Cloud Platform to distribute traffic across a set of virtual machines.


    

        
Phase 1: Prepare Your Backend (Instance Groups)

        
Before balancing traffic, you must define the servers that will handle the requests.

        
    
            
  • Create an Instance Template: 
                Go to Compute Engine > Instance templates. Define your machine type and ensure you check Allow HTTP traffic. In the networking tags, add allow-health-check.
            
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  • Create a Managed Instance Group (MIG): 
                Go to Instance groups and create a new group. Link it to your template. Set your autoscaling policy (e.g., minimum 2 instances) to ensure high availability.
            
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Phase 2: Configure the Load Balancer

        
This stage connects the internet-facing IP address to your backend servers.

        
    
            
  1. Initialize: Navigate to Network services > Load balancing. Select Create Load Balancer and choose the Application Load Balancer (HTTP/HTTPS).
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  2. Backend Configuration: 
                Create a Backend Service. Select your Instance Group as the backend. 
                
    Crucial: Create a Health Check (Protocol: HTTP, Port: 80). This allows GCP to stop sending traffic to any server that crashes.
            
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  3. Frontend Configuration: 
                Specify the protocol (HTTP or HTTPS). Reserve a Static IP Address rather than using an Ephemeral one so your website's address doesn't change unexpectedly.
            
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Phase 3: Firewall Rules & Verification

        
Traffic must be allowed to flow from the Google Cloud Load Balancer to your instances.

        
    
            
  • Allow Health Checks: In VPC Network > Firewall, create a rule allowing tcp:80 from the source ranges 130.211.0.0/22 and 35.191.0.0/16.
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  • Final Test: Copy the Frontend IP from your Load Balancer dashboard. Paste it into a browser. It may take several minutes for the initial health checks to pass before the page loads.
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