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Application Load Balancer (v2)

  • Application load balancers is Layer 7 (HTTP)
  • Load balancing to multiple HTTP applications applications across machines (target groups)
  • Load balancing to multiple applications on the same machine (ex: containers).
  • Support for HTTP/2 and WebSockets
  • Support redirects (from HTTP to HTTPS for example)
  • Routing tables to different target groups:
    • Routing based on path in URL (example.com/users and example.com/posts)
    • Routing based on hostname in url (one.example.com and other.example.com)
    • Routing based on Query String, Headers (Example.com/users?id=123&order=false)
  • ALB are a great fit for micro services & container-based applications (example: Docker & Amazon ECS)
  • Has a port mapping feature to redirect to a dynamic port in ECS
  • In comparison, we'd need multiple Classic Load Balancers per application.

Application Load Balancer Target Groups

  • EC2 instances (can be managed by an Auto Scaling Group) - HTTP
  • ECS tasks (managed by ECS itself) - HTTP
  • Lambda functions - HTTP request is translated into a JSON event

  • IP addresses - must be private IPs

  • ALB can route to multiple target groups

  • Health checks are at the target group level

Good to know

  • Fixed hostname (XXX.region.elb.amazonaws.com)
  • The application servers don't see the IP of the client directly
    • The true IP of the client is inserted in the header X-Forwarded-For
    • We can also get Port (X-Forwarded-Port) and proto (X-Forwarded-Proto)