LVS has a simple IP based persistence built-in that can be used to keep the users on the same real servers for a configurable amount of time. This has been explained in my previous post, and it works fine, but in real life users will come from various dynamic connections or even using some ISP proxy servers to browse the internet. For such situations LVS supports the configurable netmask for persistence, allowing us to increase the network mask used in the persistence match (normally we will use /24 for this) sending a bigger range of ips to the same server. This approach works fine for most cases where users will have the same class C ips allocated or the isp proxies will be on the same network range. Unfortunately this doesn’t work for AOL, because the AOL clients will always be proxied by the huge AOL proxy cluster that will send each request from a different real ip. These IPs are not even from the same range and tend to be completely different. This post will show how we can keep these AOL users on the same real server in a LVS-DR setup.

Normally if this would have been a small ISP I am sure people would have ignored their users and the users would have complained back to the ISP that they can’t reach some big sites, and in the end the ISP would have found a friendlier solution for this. Since this is AOL and they have a huge base of clients, we can’t really ignore them and we have to find a solution ourselves.

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LVS has a built-in simple IP based persistence mechanism that can be used to keep users on the same real servers for a configurable amount of time. If your web application requires that each user request to be processed by the same real server then you will probably want to enable this mechanism and ensure that requests coming from the same IP will be directed to the same real server. This article will show how you can achieve this by using regular ipvsadm commands but also by using ldirectord configurations.

IPVS is an advanced IP based load balancing application implemented inside the linux kernel. Working at IP level LVS can’t make a decisions based on the content of the packet. Still, it can perform a basic IP affinity, by keeping all connections from the same source IP directed to the same real server for a configurable amount of time. This is achieved with the -p ipvsadm command parameter and takes as a parameter the time in seconds to keep the connections in the persistence table. Read the rest of this entry »