Learn more about our Clustered Hosting System with the short FAQ below. If you have further questions or need further assistance please contact our sales dept here.
What is Clustered hosting?
A cluster is a group of servers, networked together to share the work load.
Website hosting provided by such a cluster is called Clustered hosting.
How does Clustered Hosting improve
performance and reliability?
Clustered hosting divides the website load among multiple servers, optimized
to perform their role. Each website has Service Redundancy, thereby at minimum
doubling reliability and uptime over a single server setup.
What is Service Redundancy?
Service Redundancy is state wherein each service (web, email, mySQL, cPanel.
etc) of a website have multiple points of failure. The system ensures no single
failure of hardware or software can bring the website down for prolonged periods.
How does the Service Redundancy work?
Our Windows server cluster, uses network load balancing, a patented Microsoft
algorithm, that dynamically detects and manages load on each server in cluster.
In the event of a server not responding, the system switches the requests to
alternate servers seamlessly with zero down-time.
What is Load balanced?
Load Balancing is a clustering configuration to balance network traffic across
a number of hosts, helping to enhance the performance and availability of mission
critical, IP-based services, such as Web, SMTP, MySQL and POP etc. Herein the
setup is pre-configured and monitored periodically for performance/load on individual
hosts. In real-time, load configuration switching occurs if a website service
fails completely.
What is Network load
balancing?
Network Load Balancing is a clustering technology offered by Microsoft as part
of all Windows 2000 Server and Windows Server 2003 family operating systems.
NLB uses a distributed algorithm to load balance network traffic across a number
of hosts, helping to enhance the scalability and availability of mission critical,
IP-based services, such as Web, Virtual Private Networking, Streaming Media,
Terminal Services, Proxy, etc. It also provides high availability by detecting
host failures and automatically redistributing traffic to operational hosts.
How Does the
NLB Load Balancing Algorithm Work?
NLB employs a fully distributed filtering algorithm to map incoming clients
to the cluster hosts. This algorithm enables cluster hosts to independently
and quickly make a load balancing decision for each incoming packet. It is optimized
to deliver statistically even load balance for a large client population making
numerous, relatively small requests, such as those typically made to Web servers.
When the client population is small and/or the client connections produce widely
varying loads on the server, the load-balancing algorithm is less effective.
However, the simplicity and speed of NLBs algorithm allows it to deliver very
high performance, including both high throughput and low response time, in a
wide range of useful client/server applications. If No Affinity is set, NLB
load balances incoming client requests so as to direct a selected percentage
of new requests to each cluster host; The algorithm does not dynamically respond
to changes in the load on each cluster host (such as the CPU load or memory
usage). However, the load distribution is modified when the cluster membership
changes, and load percentages are renormalized accordingly.
When inspecting an arriving packet, all hosts simultaneously perform a mapping to quickly determine which host should handle the packet. The mapping uses a randomization function that calculates a host priority based on their IP address, port, and other information. The corresponding host forwards the packet up the network stack to TCP/IP, and the other cluster hosts discard it. The mapping remains unchanged unless the membership of cluster hosts changes, ensuring that a given clients IP address and port will always map to the same cluster host. However, the particular cluster host to which the clients IP address and port map cannot be predetermined since the randomization function takes into account the current and past clusters membership to minimize remappings.
How Does NLB Cluster
Convergence Work?
Convergence involves computing a new cluster membership
list and recalculating the statistical mapping of client requests to the cluster
hosts. There are two instances in which cluster traffic has to be remapped due
to a change in cluster membership: when a host leaves the cluster and when a
host joins the cluster. A convergence can also be initiated when several other
events take place on a cluster, such as changing the load balancing weight on
a host or implementing port rule changes.
Removing a Member. Two situations cause a host to leave the cluster or go offline. First, the host can fail, an event that is detected by the NLB heartbeat. Second, a system administrator can explicitly remove a host out of the load-balancing cluster or stop NLB on that host.
The NLB heartbeat. NLB uses a heartbeat mechanism to determine the state of the hosts that are load balanced. This message is an Ethernet-level broadcast that goes to every load-balanced cluster host.
NLB assumes that a host is functioning normally within a cluster as long as it participates in the normal exchange of heartbeat messages between it and the other hosts. If the other hosts do not receive a message from a host for several periods of heartbeat exchange, they initiate convergence. The number of missed messages required to initiate convergence is set to five by default (but can be changed).
During convergence, NLB reduces the heartbeat period by one-half to expedite completion of the convergence process.
Server Failure. When a cluster host fails, the client sessions associated with the host are dropped.
After convergence occurs, client connections to the failed host are remapped among the remaining cluster hosts, who are unaffected by the failure and continue to satisfy existing client requests during convergence. Convergence ends when all the hosts report a consistent view of the cluster membership and distribution map for several heartbeat periods.
