Load balancing and high-availability clusters with iptables
STRENGTH IN NUMBERS
Iptables gives admins the ability to set up clusters and distribute the load. But what about failover?
Load sharing technologies often rely on a central system or application that distributes the work evenly over the members of the cluster. The Linux Virtual Server project implements this on Linux. To avoid a single point of failure, the central instances should be highly available and continuously monitored by a routine that checks the systems and responds to errors or lost signals. If you prefer to avoid a central load sharing instance entirely, the iptables CLUSTERIP target is an alternative. CLUSTERIP is a simple and inexpensive technique for load sharing that is already part of the Netfilter code, and although this feature is not entirely stable, the technology is quite impressive.
In CLUSTERIP, the cluster nodes share a common address, and each node uses a hash algorithm to decide whether it is responsible for a connection. Admins can assign responsibilities to a node via /proc/net/ipt_CLUSTERIP, influencing load sharing, or switching interactively or by means of dynamic scripting. Stonesoft products have had this functionality for a while, and it works well.
Iptables clusters do not have a built-in heartbeat mechanism to check the health state of the nodes, remove broken systems from the cluster, or tell other nodes to take over the load of the failed system. Many failures are heralded by tell-tale signs, however, that give the ailing node the ability to voluntarily leave the cluster in good time. In this article, I show the possibilities of combining the CLUSTERIP target of iptables with a script controlling the cluster.
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Fedora Asahi 40 Remix Available for Macs with Apple Silicon
If you've been anticipating KDE's Plasma 6 for your Apple Silicon-powered Mac, then you're in luck.
-
Red Hat Adds New Deployment Option for Enterprise Linux Platforms
Red Hat has re-imagined enterprise Linux for an AI future with Image Mode.
-
OSJH and LPI Release 2024 Open Source Pros Job Survey Results
See what open source professionals look for in a new role.
-
Proton 9.0-1 Released to Improve Gaming with Steam
The latest release of Proton 9 adds several improvements and fixes an issue that has been problematic for Linux users.
-
So Long Neofetch and Thanks for the Info
Today is a day that every Linux user who enjoys bragging about their system(s) will mourn, as Neofetch has come to an end.
-
Ubuntu 24.04 Comes with a “Flaw"
If you're thinking you might want to upgrade from your current Ubuntu release to the latest, there's something you might want to consider before doing so.
-
Canonical Releases Ubuntu 24.04
After a brief pause because of the XZ vulnerability, Ubuntu 24.04 is now available for install.
-
Linux Servers Targeted by Akira Ransomware
A group of bad actors who have already extorted $42 million have their sights set on the Linux platform.
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.
-
XZ Gets the All-Clear
The back door xz vulnerability has been officially reverted for Fedora 40 and versions 38 and 39 were never affected.