This is used for inbound server load balancing, by ensuring that all socket connections from the same client/user/IP on the internet goes to the same server on your local server pool.
This works great for ensuring simplified memory management of session artefacts on the application being hosted (the servers do not have to synchronise the users session data as extra sockets from that user will always connect to the same local server)
However sticky-address does not have an equivalent for sticky destination IPs. For example when doing outbound load balancing over multiple ISP links, every single socket is load balanced randomly. This causes many websites to break (especially cookie login and single-sign-on style enterprise services), as the first outbound socket will originate randomly from one of the local ISP IPs, and the users login session/SSO (on the server side) will belong to that first random IP.
When the user then browses to or uses another part of that same website which requires additional sockets, the additional sockets will pass the SSO credentials from the first socket, but the extra socket connection will again be randomly load-balanced, and so the remote server will reject the connection as it is originating from the wrong source IP etc.
Therefore can I please propose a “sticky-address for destination IPs” as an analogue to the existing sticky-address for source IPs?
This is now such a problem that we have to use sticky-address even on outbound load-balancing connections, which causes internal user1 to always use the same ISP for _everthing_ etc. While this does stop the breakage, it does not result in evenly distributed balancing of traffic, as users are locked to one single transit, for all their web browsing for the rest of the day after being randomly balanced once first-thing in the morning, rather than all users balancing over all transits throughout the day.
Another pain; using the current source-ip sticky-address for outbound balancing, makes it hard to drain transits for maintenance. For example without source sticky-address balancing, you can just remove the transit from the Pf rule, and after some time, all traffic will eventually move over to the other transits, allowing the first to be shut down for whatever needs. But with the current source-ip sticky-address, that first transit will take months to drain in a real-world situations..
lastly just as a nice-to-have, how feasible would a deterministic load balancing algorithm be? So that balancing selection is done based on the “least utilised” path?
Thanks for your time and consideration,
Kindest regards Andy
Sent from a teeny tiny keyboard, so please excuse typos.