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/Weird loadbalancing behavior from Classic ELB/

Weird loadbalancing behavior from Classic ELB


We have 4x EC2 instances with httpd web server scattered across B and D zones. In random times of the day, one of the instances in Zone B would get none of the traffic and have its traffic rerouted the other EC2 instance in that zone.

The user-traffic would be like this:

  1. Zone B, Instance 1 - 50%
  2. Zone B, Instance 2 - 0%
  3. Zone D, Instance 3 - 25%
  4. Zone D, Instance 4 - 25%

I mentioned user-traffic above because the traffic from health checks during this period are equal across all machines and all of them are fine.

After 5 minutes it would return back to normal.

Any help would be appreciated.