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ELB SOA

Links: 114 AWS SOA Index

Target group settings

  • deregisteration_delay.timeout_seconds: time the load balancer waits before deregistering a target
  • slow_start.duration_seconds: duration of cold start
  • load_balancing.algorithm.type: how the load balancer selects targets when routing requests (Round Robin, Least Outstanding Requests)
  • stickiness.enabled
  • stickiness.type: application-based or duration-based cookie
  • stickiness.app_cookie.cookie_name: name of the application cookie
  • stickiness.app_cookie.duration_seconds: application-based cookie expiration period
  • stickiness.lb_cookie.duration_seconds: duration-based cookie expiration period

Slow start mode

  • By default, a target receives its full share of requests once it's registered with the target group.
  • Slow Start Mode gives healthy targets time to warm-up before the load balancer sends them a full share of requests.
  • The load balancer linearly increases the number of requests that it sends to the target
  • A target exits Slow Start Mode when:
    • The duration period elapses
    • The target becomes unhealthy
  • To disable, set Slow start duration value to O

Request routing algorithms

  • Least Outstanding requests:
    • The next instance to receive the request is the instance that has the lowest number of pending/unfinished requests.
    • Works with Application Load Balancer and Classic Load Balancer (HTTP/HTTPS)
    • CANNOT be combined with slow start.
  • Round Robin:
    • Equally choose the targets from the target group.
    • Works with Application Load Balancer and Classic Load Balancer (TCP)
  • Flow Hash:
    • Only for NLB.
    • Selects a target based on the protocol, source/destination IP address, source/destination port, and TCP sequence number.
      • attachments/Pasted image 20230303082635.jpg
    • Each TCP/UDP connection is routed to a single target for the life of the connection.

Rules

  • Rules are setup on the load balancer and we can have many rules.
  • Rules are processed in order and default rule is processed at the last.
  • Supported Actions (forward, redirect, fixed-response)
  • Rule conditions (same as different types of routing in ALB): host-header, http-request-method, path-pattern, source-ip, http-header, query-string
  • For a single rule we can have multiple target groups and we can specify the weighting of each group.
    • Example: multiple versions of your app, blue/green deployment

Miscellaneous

  • In certain scenarios, such as when flash traffic is expected, or in the case where a load test cannot be configured to gradually increase traffic, AWS recommends that you contact AWS to have your load balancer "pre-warmed".
    • AWS will then configure the load balancer to have the appropriate level of capacity based on the traffic that you expect.

Last updated: 2023-03-22