Elastic Load Balancing provides three different types of load balancers:

  • Application Load Balancers operate at layer 7 and are capable of host- and path-based routing. They have HTTP/2, WebSockets and IPv6 support. ECS dynamic port mapping is supported.
  • Network Load Balancers L4?
  • Classic Load Balancers operate at layer 4, with layer 7 awareness. They support EC2-Classic, non-HTTP TCP and SSL listeners and have support for sticky sessions using application-generated cookies.


All ELB instances are given a randomly generated hostname under <region>.elb.amazonaws.com, providing a stable name for CNAMEs that can be used across AZs.

Cross-zone load balancing

Cross-zone load balancing allows you to define the traffic split across AZs.

load balancer nodes scale relative to demand, but we only see a single logical resource


Once enabled, access logs are written to objects named:

s3://<bucket>[/<prefix>]/AWSLogs/<account id>/elasticloadbalancing/<region>/<yyyy>/<mm>/<dd>/<account id>_elasticloadbalancing_<region>_<alb id>_<end time>_<ip address>_<random>.log.gz

The log entries include information about both the request and response action.


Timing information is split across three metrics:

  • request_processing_time contains the total elapsed time, to ms precision, from receipt of the request until dispatch to a target.
  • target_processing_time contains the total elapsed time, to ms precision, from dispatch to a target until the target began sending response headers.
  • response_processing_time contains the total elapsed time, to ms precision, from the target's delivery of headers to the load balancer beginning delivery to the client.

  1. ALB
  2. Classic
  3. NLB