Question

I have a F5 load balancer that directs traffic to 2 web servers with one having a higher priority than the other so all traffic gets sent to it. If the higher priority server goes down this would mean all traffic would get directed to the lower priority server.

My question is if somebody is directed to the lower priority server because the high priority server is down and then the higher priority server comes back up again will the exisiting connections be maintained to the lower priority server.

I ask because I am being told that they would stay connected to the lower priority server because the TCP connection would remain open. I thought HTTP connections open and close when an object is downloaded so this would be continuously creating new connections and be directed to the high priority server when it came back up.

Answer 1

HTTP connections are not necessarily opened and closed on a per request basis anymore, in fact with HTTP/1.1 the default is to have a connection remain open, so that multiple requests done in short order (such as would happen with loading images and scripts on a webpage) could dispense with the connection setup and teardown overhead. I’ll point you to the rfcs for more info on that.

Now with the caveat that my background isn’t in configuring load balancers…

• If your load balancer is acting like an HTTP Proxy (and not just a glorified router) just because the client machine has a persistent connection with the load balancer doesn’t necessarily mean the load balancer has a persistent connection with your server (the connection header applies on a per-segment basis per the rfc.
• If your load balancer is configured to do any form of session affinity / sticky sessions, a client that connects to the lower server might have future connections stick to the lower server.