High-Availability Cluster with Linux-

HAMatt Varnell Cameron Adkins Jeremy Landes

Computer Cluster

A group of linked computers, working together as a single computer.

Computers connected to each other through fast local area networks.

Used to improve performance and reliability over that of a single computer.

High-Availability Cluster

Implemented to improve the availability of services that clusters provide.

Redundant nodes are used to provide replacement services when system components fail. Redundant nodes means same OS, data, system clocks,

etc.

Most commonly consist of two nodes (minimum requirements)

This system eliminates single points of failure from bringing down the entire cluster.

Running a single server setup after crashing

This leads to any tasks needing to go through the server or use software from it to be put on hold until the problem is solved.

A system administrator would have to fix the issue before the server could be used again.

Solution: A High-availability Cluster setup.

If the main node crashes, there is a secondary node available with redundant data that will immediately start running in the case of a primary crash.

No outside assistance needed to bring the system back up in case of a crash.

Node Configuration

Active/Active (traffic is load balanced across available nodes)

Active/Passive (all nodes are fully redundant – hardware heavy setup)

N+1 (single extra node brought online in the case of a node failure)

Also N+M, N-to-1, N-to-N (variations on the N+1 model depending on system setup)

Heartbeat Architecture

Two systems share a heartbeat over a private closed loop. Consists of a sequence of simple messages using checksums to

ensure normal activity.

If heartbeat is lost, the secondary node acquires resources from the primary node.

Uses redundant physical loops to monitor heartbeat between the systems: Serial ports: Two node monitoring using a serial cable plugged

into both devices. Ethernet ports: Uses a crossover cable and private IP network

between both hosts.

Linux-HA

The Linux HA working group (Linux.org) has developed a heartbeat architecture that supports a wide array of HA internode communications mechanisms and media.

Linux-HA

Works to provide a high availability clustering solution for Linux, Solaris and Mac OS X.

Main software product of this project is Heartbeat, a cluster management program for HA clustering.

Features: No fixed maximum number of nodes (from very small

to large clusters) Resource monitoring (automatic resource allocation) Fencing mechanisms (failed node removal)

Work Citied

http://www.tech-faq.com/high-availability-clusters.html

http://gw5kw3uf8g.search.serialssolutions.com.lib-proxy.radford.edu/?genre=article&isbn=&issn=01921541&title=Electronic+Engineering+Times+%2801921541%29&volume=&issue=1112&date=20000508&atitle=Building+Linux+high-availability+systems.&aulast=Ramsey%2c+Brian&spage=92&pages=92-95&sid=EBSCO:Academic+Search+Complete&pid=

http://www.linux-ha.org/wiki/Main_Page

http://www.centos.org/docs/5/html/Cluster_Suite_Overview/s1-clstr-basics-CSO.html