What are the differences between Windows Clustering, Network Load Balancing and Round Robin, and scenarios for each use?

Cluster technologies are becoming increasingly important to ensure service offerings meet the requirements of the enterprise. Windows2000 and Windows Server2003 support three cluster technologies to provide high availability, reliability and scalability. These technologies are: NLB, CLB and Server cluster. These technologies have a specific purpose and are designed to meet different requirements. Server cluster provides failover support for applications and services that require high availability, scalability and reliability, and is ideally suited for back-end applications and services, such as database servers. Server cluster can use various combinations of active and passive nodes to provide failover support for mission critical applications and services. NLB provides failover support for IP-based applications and services that require high scalability and availability, and is ideally suited for Web tier and front-end services. NLB clusters can use multiple adapters and different broadcast methods to assist in the load balancing of TCP, UDP and GRE traffic requests. Component Load Balancing provides dynamic load balancing of middle-tier application components that use COM+ and is ideally suited for application servers. CLB clusters use two clusters. The routing cluster can be configured as a routing list on the front-end Web servers or as separate servers that run Server cluster. Cluster technologies by themselves are not enough to ensure that high availability goals can be met. Multiple physical locations may be necessary to guard against natural disasters and other events that may cause complete service outage. Effective processes and procedures, in addition to good architecture, are the keys to high availability. Round robin is a local balancing mechanism used by DNS servers to share and distribute network resource loads. You can use it to rotate all resource record (RR) types contained in a query answer if multiple RRs are found. By default, DNS uses round robin to rotate the order of RR data returned in query answers where multiple RRs of the same type exist for a queried DNS domain name. This feature provides a simple method for load balancing client use of Web servers and other frequently ueried multihomed computers. If round robin is disabled for a DNS server, the order of the response for these queries is based on a static ordering of RRs in the answer list as they are stored in the zone (either its zone file or Active Directory).

If I had to give a simple answer; I'd say;  Windows Clustering is a method of using2 or more Servers to provide a higher level of availability, reliability, and scalability.

Where in NLB (Network Load Balancing) is another clustering technology that combines the multiple clustered Servers (called hosts) to get a high availability for web-based services like FTP Servers, Proxy Servers, Terminal Services, virtual private networking, and streaming media servers.

Round-robin is another load-balancing technique which utilizes a DNS server instead of having the actual dedicated server hardware.

Windows Clustering can be used in Application servers, ERP severs, database Servers. Exchange Server Clustering is also based in Windows Clustering.

As I mentioned above, NLB can be used in web based services to get uninterrupted service uptime.

If you have a multiple webservers hosted in different part of the world, the Round-robin technique is used.

Hi,

All of the three features are different and they used in different scenarios as the following:

Failover Clustering: this is a high availability feature, it allows multiple server to work together to keep the service or application high available in a system, FC is used with roles and applications that are stateful like: file servers, print server, DHCP and server have databases like mail, the failover clustering requires SAN because the data that you want to keep it high available (like DBs) should not be on servers but should be on redundant SAN.

NLB: feature is responsible in distributing traffic across multiple server configured in one NLB cluster, NLB is used with stateless applications like Web Server, VPN, Terminal Server, CAS Server (in Exchange), so NLB provide load balancing which means all the requests send to a website (for example) will be distributed to the servers which reduce the load on the servers, increase performance, and provide availability in case one server is down.

Round Robin: A DNS feature enabled by default in Microsoft DNS servers, this service used if you have a specific name for example: mail.domain.com and you have more than one mail server, in this case we go to DNS and create2 or3 A records based on the number of mail servers, all these records should have the name: mail.domain.com but the IP in every record is the IP of your server, se bellow:

Host (A) Record1: Name: mail.domain.com ---IP:10.10.10.10

Host (A) Record2: Name: mail.domain.com ---IP:10.10.10.11

Host (A) Record3: Name: mail.domain.com ---IP:10.10.10.12

Now if a query comes to your DNS asking about mail.domain.com, the round robin feature will respond and say it is10.10.10.10, if another query comes and asks about mail.domai.com the round robin feature will respond and say it is10.10.10.11 and so on.

It is important to know that the best practice is to separate the NLB and Failover clustering servers, also if you will use NLB do not use round robin and if you will use round robin do not use NLB.

Also some IT professionals use Hardware load balancers instead of Microsoft NLB and DNS round robin.

HTH

Best Regards,