Application Load Balancer (v2)

Layer 7

• Application load balancers is Layer 7 (HTTP)

• Load balancing to multiple HTTP applications across machines (target groups)

• Load balancing to multiple applications on the same machine (ex: containers)

• Support for HTTP/2 and WebSocket

• Support redirects (from HTTP to HTTPS for example)

• Routing tables to different target groups:

  • Routing based on path in URL (example.com/users & example.com/posts)

  • Routing based on hostname in URL (one.example.com & 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 application (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 Balancer per application.

Possible Target Groups of ALB

• 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)

HTTP Based Traffic

Query Strings/Parameters Routing