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Advantages of three working modes of LVS
First, Virtual Server Via Nat (VS-NAT)
??? Advantages: The physical server in the cluster can use any support TCP / IP operating system, the physical server can allocate the IP address of the Internet, only the load balancer requires a legal IP address.
??? Disadvantages: Limited expansion. When the server node (ordinary PC server) increases to 20 or more, the load balancer will become the bottleneck of the entire system, as all request packages and answering packages need to be regenerated by the load balancer. If the average length of the TCP package is 536 bytes, the average package reproduction delay time is approximately 60 su (calculated on the Pentium processor, the faster processor will make this delay time becomes short), the maximum allowable allowance of the load balancer The capability is 8.93m / s, assuming that the platform allowable capacity of each physical server is 400k / s, responsible for the calculation of 22 physical servers.
??? Solution: Even if the load balancer is a bottleneck of the entire system, there are two ways to solve it. One is a mixing process, and the other is the use of Virtual Server Via IP Tunneling or Virtual Server Via Direct Routing. If a mixed process is employed, there will be a number of separate RR DNS domains. You use Virtual Server Via IP Tunneling or Virtual Server Via Direct Routing to get better scalability. It is also possible to nested the load balancer, at the foremost, the VS-Tunneling or VS-DROUTING load balancer, and then use the load balancer of VS-NAT.
Second, Virtual Server Via IP Tunneline (VS-TUN)
??? We found that many Internet services (such as web servers) are short, and the answer package is usually large.
??? Advantages: The load balancer is only responsible for sending the request package to the physical server, and the physical server issues the answering package directly to the user. Therefore, the load balancer can handle a huge amount of request. This way, a load balancing can be more than 100 physical server services, and the load balancer is no longer the bottleneck of the system. With VS-TUN mode, if your load balancer has 100M full-duplex network card, the entire Virtual Server can reach 1G throughput.
Insufficient: However, this way requires all the servers to support the "IP Tunneling" protocol, I only implemented this on the Linux system, if you can support other operating system support, still explore.
Third, Virtual Server Via Direct Routing (VS-DR)
??? As the VS-TUN, the load balancer is only distributed, and the answering package returns to the client through a separate routing method. This implementation of VS-DR does not require tunnel structures compared to VS-TUN, so most operating systems can be used as physical servers, including: Linux 2.0.36, 2.2.9, 2.2.10, 2.2.12 Solaris 2.5.1, 2.6, 2.7; FreeBSD 3.1, 3.2, 3.3; NT4.0 No need to make patch; IRIX 6.5; HPUX11, etc.
Insufficient: NIC requests the load balancer must be on a physical segment with the physical network card.
