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.
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.
- 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
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
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.
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