What is SG Cluster?
There are mainly three types of clusters: scientific clusters, load
balancing clusters and high availability clusters.
Scientific clusters are often used to develop parallel programming applications
for a cluster to solve complex scientific problem. They use commodity
systems such as a group of single-or-dual processor PCs linked via high-speed
connections and communicating over a common messaging layer instead of
expansive supercomputers.
Load balancing clusters share the processing load or network traffic
load as evenly as possible across a cluster of computers. Such system
is perfectly suited for large number of users running the same set of
applications.
High availability clusters keep the overall service of the cluster available
as much as possible by taking into account the fallibility of computing
hardware and software.
The SG cluster is a mixture of load balancing cluster and high availability
cluster. It enables you to create load balancing, fault tolerant and high
availability cluster for most existing applications, especially for the
Internet services. A typical SG Cluster contains one or two load balancers
and several back-end servers. It has the following features:
Manageable - It is very simple to install and a friendly web user interface
is available to ease the administration.
Single Image - It transparently clusters back-end servers running different
platforms into a single system that appears as a single server to the
client
Scalable - The system service capacity can be increased by adding
new servers to the cluster
Load Balancing - It automatically routes incoming requests to the least
loaded servers for optimal performance.
Fault Tolerant - SG load balancer monitors the availability of back-end
servers and only routes client's requests to those alive ones. More
than one load balancers can be setup to avoid the single point of failure
in the whole system.
High Availability - SG cluster can mask the faults on load balancer
or back-end servers if there are sufficient redundancies. It also keeps
service available when doing system upgrade.
ps: the SG cluster is based on the FreeBSD
NAT implementation and the SG floppy distribution is created with the
PicoBSD toolkit.
Hardware Requirement
- CPU 80386 or above (Pentium133 recommended)
- RAM 12 MB or more (64MB recommended)
- one 1.44 floppy drive
- two Ethernet LAN cards
ed - NE2000, 3com 3C503 (ed0 port 0x300 irq10, ed1 port 0x320 irq11)
Download
- fdimage
A dos tool to dump SG image to floppy disk.
It could be executed under dos/win95/98/2k/xp
- SG utilities
These are SG utilies executed either on backend server or remotely.
Binaries for the following platforms are available:
FreeBSD - static linked
Linux - static linked
Solaris- dynamic linked on solaris 8 x86
Trouble Shooting
- login on the SG console and type 'ifconfig -a' to see if the interfaces
have been correctly detected.
- telnet to a host on the public Internet from SG load balancer to check
if the setting of public interface is correct or not.
- telnet to a server in the private subnet from SG load balancer to
check if the setting of private interface is correct or not.
- type 'ps' on SG console, check if all SG related process are there,
including bidd, natd, mrouted, sgctrld and sgmon.
- if bidd is missing, there may be error in network address setting
- if only bidd exists, maybe there is another primary SG load balancer
or natd_parameter error in sg.conf
Todo
- stateful recovery of SG load balancer
- better port test for sgmon
- distributed authentication gateway on SG load balancer
- distributed load balancer through DNS
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