August 10, 2010

Red Hat Cluster Suite

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The Red Hat Cluster Suite includes software to create a high availability and load balancing cluster, it currently does not contain functionality for distributed computing (see below).

High Availability Cluster
A Red Hat cluster suite when configured for high availability attempts to ensure service availability by monitoring other nodes of the cluster. All nodes of the cluster must agree on their configuration and shared services state before the cluster is considered Quorate and services are able to be started.

The primary form of communicating node status is via a network device (commonly Ethernet), although in the case of possible network failure, quorum can be decided through secondary methods such as shared storage or multicast.

Software services, filesystems and network status can be monitored and controlled by the cluster suite, services and resources can be failed over to other network nodes in case of failure.

The Cluster suite forcibly terminates a cluster node's access to services or resources to ensure the node and data is in a known state. The node is terminated by removing power or access to the shared storage.

Service locking and control is guaranteed through fencing and STONITH, more recent versions of Red Hat use a distributed lock manager (DLM), to allow fine grained locking and no single point of failure. Earlier versions of the cluster suite relied on GULM (Grand Unified Lock Manager) which could be clustered, but still presented a point of failure) if the nodes acting as gulm servers were to fail. GULM as a locking manager is available but deprecated in Red Hat Cluster Suite 5.

Technical Details

  • Support for up to 128 nodes ( 16 on Red Hat Enterprise Linux 3 and 4)

  • NFS (Unix) /CIFS (Windows)/GFS (Multiple Operating systems) File system failover support

  • Service failover support

  • Fully shared storage subsystem

  • Comprehensive Data Integrity

  • SCSI and Fibre Channel support
Load balancing Cluster
Red Hat adapted the Piranha load balancing software to allow for transparent load balancing and failover between servers. The application being balanced does not require special configuration to be balanced, instead a Red Hat Enterprise Linux server with the load balancer configured, intercepts and routes traffic based on metrics/rules set on the load balancer.

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