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Heartbeat: free, open source software for Linux high availability

Many organizations are finding that the savings they achieve by migrating servers to Linux can more than pay for the added high availability guarantee of redundant systems. The additional cost in adding a redundant server with failover is not likely to be much more than the additional hardware cost.

Failover is defined as activating redundant servers to replace servers that have become unavailable. The grouping is typically one primary server and one secondary server. This process can be configured to happen automatically, and it most typically used for web servers, mail servers, database servers, firewalls, file servers, DNS servers, or any server for which high availability is a priority.

In order for a secondary server to take over for a primary server that has become disabled, it needs to be aware of the primary server's condition. A message is continuously sent between the servers to notify each other of their existence, usually via a special hardware cable. A signal goes over the cable continuously, at a regular rapid intervals. If messages are not received from the primary server, it is considered to have gone off line, and all resources that it owned are failed over to the secondary server.

Heartbeat (linux-ha.org) is a free, open source product widely used to configure failover redundancy. The project got its start in 1998, and has been in production status since 2000. The lead developer, Alan Robertson, is a full time employee of IBM. Intel is also a sponsor, contributing developers on their payroll. Heartbeat is included free with every distribution except Red Hat, and Red Hat users can simply download it. A major goal of the Heartbeat project is to provide flexibility, so users are able to configure the software in a variety of ways. Security is also important, so all packets are digitally signed.

Heartbeat Features

  • Free open source failover software
  • Allows server redundancy at very low cost
  • Flexible - variety of configurations possible
  • Can also achieve data replication with DRBD project in conjunction with Heartbeat
  • Secure - packets are digitally signed
  • Webmin module available
The project is planning to expand to support larger clusters, and will add additional monitoring features. In the future, they would also like to monitor hardware temperature to detect imminent failure. The project is currently adding full time developers to achieve these goals.

Commercial support is provided by Tummy.com (http://tummy.com). Most Linux consulting groups also deploy and support redundancy with Heartbeat. The project mailing lists (http://www.linux-ha.org/contact/) are known for being especially helpful to those new to the product. The November 2003 issue of Linux Magazine (http://linux-mag.com) ran an article by the lead developer on using Heartbeat in a typical configuration.

The DRBD (Distributed Replicated Block Device) project allows for a software RAID on Linux at a very low cost. DRBD is an open source project (http://sourceforge.net/projects/drbd/) dedicated to data replication, and is frequently being used in conjunction with Heartbeat.

 

Last month's featured project

phpWebsite is a free, open source content management system developed by Appalachian State University in Boone, NC. A modular design and the use of PHP make it easy to create custom functionality through drop-in modules, making it a platform for rapid web development. Several modules are included in the core installation, such as calendaring, email, a photo album, form generators, polling, and the facility for website visitor interaction such as posting notes.

 

Read more on website.technology.


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