What is your health check settings for elastic load balancer? I am not really well into this as my goal is to get the good settings to put where the ELB immediately failover the traffic when my 1st ec2 instance is down to the 2nd ec2 instance. Can anyone mind to share their configuration and knowledge?
Thanks. James
Health check settings in ELB are important, but usually not that important.
1) ELB doesn't support active/passive application instances - only active/active. 2) If an application stops accepting connections or slows dramatically, load will automatically shift to the available / faster instances. This happens without the help of health checks. 3) Health checks prevent ELB from having to try to send a request to an instance in order to find out it is not well. This is good because a request to an unhealthy back end can sacrifice the request (an error will be sent to the client). 4) If your health check settings are too sensitive (such as using a 1 second timeout when some percent of your requests take longer than that) then it can pull instances out of service too easily. Too much of this and your site will appear to be down from time to time.
If you are trying a scenario with multiple availability zones and only one back-end in each zone, then the health checks are more important. If there are NO healthy back-ends in a zone, ELB will try to forward requests to another zone that has at least one healthy instance. In this case, the frequency of health checks determines the failover time, so you'll want faster checks.
