Debian

A cluster is a group of systems that work together in such a way that the whole functions as a single unit. Such clusters can be loosely coupled or tightly coupled. A loosely coupled environment, each system is complete in itself, and can handle all of the tasks any of the other systems can handle. The environment provides mechanisms for redundancy, load sharing, and fail-over between systems, and is often called a High Availability (HA) cluster.

There are other packages that can be used to manage a distributed environment, such as Chef and BCFG2. While simpler than Puppet or FAI, they support similar functions and have been used in some distributed and clustered environments.

The use of FAI, Puppet, and others in cluster management warrants a brief look at clustering next, and what packages in Debian support clustering.

Probably the best known application for distributed management is Puppet, developed by Puppet Labs. Unlike FAI, only the Open Source edition is free, the Enterprise edition, which has many additional features, is not. Puppet does include support for environments other than Linux. The desired configuration is described in a custom, high-level definition language, and distributed to systems with installed clients. Unlike FAI, Puppet does not provide its own bare metal remote installation method, but does use existing methods (such as kickstart) to provide this function.

Fully Automated Installation (FAI) focuses on managing Linux installations, and is developed using Debian, although it works with many different distributions, not just Debian. FAI uses a class concept for categorizing similar systems, and provides a good deal of flexibility and customization via hooks. F AI provides for unattended, automatic installation as well as tools for monitoring and updating groups of systems. FAI is frequently used for creating and maintaining clusters. More information is available at http://fai-project . org/.

One of the issues frequently faced by administrators is that of having multiple, remote systems all with similar software for the most part, but with minor differences in what is installed or running. Debian provides several packages that can help manage such an environment in a unified manner. Two of the more popular packages, both available in Debian, are FAI and Puppet. While we don't have the space to go into details, both applications are described briefly here.

Of course, backups are not the only issue with managing multiple, remote systems. In particular, managing such multiple configurations using a centralized application is often desirable.

Of course, Debian offers other backup packages as well. They are less complex than Amanda or Bacula, but more suited to smaller environments. Most use standard file archiving utilities, and offer remote storage options (either via standard remote file specification or by using a client and server approach). Some offer backup cycle management utilities, backup encryption, communications encryption, and even deduplication when using special backup storage formats. Synaptic or apt-cache can be used to search for these packages using the search term backup.

Bacula is another popular free backup package. Itis designed to be more modular than Amanda. Like Amanda, itrequires a client on the system to be backed up. In addition to the client, however, there is an administrative console service, a status monitor service, a backup director which controls the actual backup operations, a storage service that keeps the actual backup data, and a database service where the backup information and catalogs are mamtained.

For many years, the University of Maryland (UoM) Computer Science department was the source of quality, free software that rivaled or even surpassed proprietary solutions. The Advanced Maryland Automatic Network Disk Archiver (AMANDA), is one such solution. Although no longer supported by UoM, it is now hosted on SourceForge, where it remains in active development. In addition to the free Community edition, there is a paid Enterprise edition that includes additional features, such as a graphical configuration utility.

If you're in charge of one or more systems that are installed at a distant location, backing them up individually can be a large chore. Fortunately, there are a number of packages that can help. Most backup packages, even those intended to create a backup of a single machine, have options to send the data to a remote location for actual storage. Ofcourse, any of the packages with this capability can be used on multiple machines.