AWS Application Load Balancer (ALB) Rules Overview

• Rules Configuration:
  • Rules are set up on your ALB.
  • You can have multiple rules, with the last one being the default rule.
  • Each rule directs traffic to a specific target or action.
• Rules Processing:
  • Rules are processed in the order they are set.
  • The default rule is processed last.
• Supported Actions:
  • Forwarding to a target group.
  • Redirecting to a different URL.
  • Sending a fixed response.
• Rule Conditions:
  • Host header: Based on the client request's host.
  • HTTP request method: Identifies if the request is GET, POST, PUT, etc.
  • Path pattern: Directs requests to specific paths like /myapp1 or /myapp2.
  • Source IP: Filters requests based on the originating IP address. https://repost.aws/knowledge-center/elb-route-requests-with-source-ip-alb
  • HTTP headers: Uses specific headers to route requests.
  • Query string parameters: Utilizes the request's query parameters.
• Multiple Target Groups:
  • A single rule can forward to multiple target groups.
  • Weights can be assigned to each target group within a rule.
• Weighted Target Groups:
  • Allows for controlled traffic distribution between different versions of a service.
  • Facilitates blue-green deployments.
  • Example: 80% of traffic to target group one (blue), 20% to target group two (green).

• Monitoring and Evaluation:
  • Enables monitoring of target groups to ensure they handle traffic correctly.
  • Allows assessment of new application versions based on performance metrics.

Example Scenario

• Historical Setup:
  • Users communicate with the ALB.
  • ALB is configured to route traffic to target group one (blue).
• New Setup:
  • A second target group (green) is introduced for a new version of the application.
  • Rule weights are configured: 8 for target group one, 2 for target group two.
  • ALB now routes 80% of traffic to the first group and 20% to the second group.
  • This setup allows for performance monitoring and validation of the new application version.

Conclusion

• The lecture covered the importance of ALB rules for directing traffic and facilitating service updates through blue-green deployments. The ability to assign weights to target groups within a rule is a powerful feature for gradually introducing new versions of an application while monitoring their performance.