AWS ELB(ALB)

Overview

• Layer 7 (advanced)
  • Content based routing
• Evaluates listener rules
• Use cases
  • Single LB fronting different types of services (e.g. website, api)
  • Microservices in containers (integrated wih ECS)
• Improved performance over ELB (cheaper)
• Integrated with WAF
• IPv6 support

Types

• Internet facing
• Internal

Limitations

• No backend authentication (unlike CLB)

Listeners

• HTTP/HTTPS
  • Ports 1-65535
• HTTPS
  • Multiple certificates possible (SNI)
    • Smart selection if 
• WebSockets
  • HTTP (ws://) or HTTPS (wss://)
• HTTP/2
  • HTTPS listeners only
  • Server-Push not available
• Has Listener Rules (1+)

Listener Rule

• Contains
  • Priority
  • Action
    • Always forward request
  • Optional Host
    • Host-based routing
  • Optional Path
    • Path-based routing
• Default rule has no conditions (catch-all)

Target

• Type
  • EC2 instance
  • IP address
    • Inside/outside VPC (e.g. on-premise)
    • IP must be private
      • ClassicLink instances
      • Peered-VPC
      • On-premise instances (Direct Connection/VPN)
        • Use case: migrate-to-cloud/burst-to-cloud/fail-over-to-cloud
• State
  • draining
• Same target may be registered multiple times (different ports) e.g. microservices

Target Group

• Set of targets
• Listener rule forwards traffic to Target Group
• Has its own HealthCheck
  • If no healthy targets still routes traffic
• You don't need to take the whole instance out of rotation
• May be attached to Auto Scaling Group

Request Tracing

• LB injects a header X-Amzn-Trace-Id
• Supports chaining: Field={Root, Self}
• Visible in Access Logs ("trace_id")

Sticky Sessions

• Only LB cookie supported (AWSALB)
• Websockets are inherently sticky (long-lasting connection)

Healthchecks

• Ability to define "successful" HTTP status codes

Pricing

• Per-hour fee
• LCU
  • Dimenstions
    • 3000 Active Connections per minute
    • 25 new connections established per second
      • Certificate key size matters (shorter = cheaper)
    • 1000 rules evaluation
    • Data transferred 2.25 Mbps (=1 GB/per-hour)
  • Highest dimension used to evaluate number of LCUs consumed 

References

• https://docs.aws.amazon.com/elasticloadbalancing/latest/application/doc-history.html
• https://github.com/open-guides/og-aws#alb
• https://aws.amazon.com/blogs/devops/introducing-application-load-balancer-unlocking-and-optimizing-architectures/
• https://aws.amazon.com/blogs/aws/new-application-load-balancing-via-ip-address-to-aws-on-premises-resources/