SUBMITTED BYLATIKA WADHWANIVIII SEM , CS –A2

ROLL NO –58

SUBMITTED TO : MS. NEHA AGRAWAL

MS. RIMJHIM JAIN

Load Balancing on Internet

Introduction Server load balancing Types of load balancing Load balancing algorithms Linux virtual server Methods of load balancing

Table Of Contents

Load balancing is a computer networking methodology to distribute workload across multiple computers or a computer cluster, network links, central processing units, disk drives, or other resources, to achieve optimal resource utilization, maximize throughput, minimize response time, and avoid overload

What Is Load Balancing

Load balancing in internet is done to provide a single Internet service from multiple servers, sometimes known as a server farm.

A client sends a request to the virtual server, which in turn selects a physical server in the server farm and directs this request to the selected physical server.

Server load balancing

When multiple web servers are present in a server group, the HTTP traffic needs to be evenly distributed among the servers. In the process, these servers must appear as one web server to the web client, for example an internet browser. The load balancing mechanism used for spreading HTTP requests is known as IP Spraying.

The equipment used for IP spraying is called, the 'load balancer'

Load Balancing Mechanism

Round robin dns : multiple IP addresses are associated with a single domain name.

Hardware load balancing : Hardware load balancers can route TCP/IP packets to various servers in a cluster.

Software load balancing :  listening on the port where external clients connect to access services. The load balancer forwards requests to one of the "backend" servers, which usually replies to the load balancer.

Ways of load balancing

Random allocation Round robin allocation Weighted round robin allocation Least connections

Load Balancing Algorithms

In a random allocation, the HTTP requests are assigned to any server picked randomly among the group of servers. In such a case, one of the servers may be assigned many more requests to process, while the other servers are sitting idle. However, on average, each server gets its share of the load due to the random selection.

Pros: Simple to implement. 

Cons: Can lead to overloading of one server while under-utilization of others

Random Allocation

In a round-robin algorithm, the IP sprayer assigns the requests to a list of the servers on a rotating basis. The first request is allocated to a server picked randomly from the group. For the subsequent requests, the IP sprayer follows the circular order to redirect the request. Once a server is assigned a request, the server is moved to the end of the list. This keeps the servers equally assigned.

Pros: Better than random allocation because the requests are equally divided among the available servers in an orderly fashion.

Cons: Round robin algorithm is not enough for load balancing based on processing overhead required and if the server specifications are not identical to each other in the server group.

Round-Robin Allocation

Weighted Round-Robin is an advanced version of the round-robin that eliminates the deficiencies of the plain round robin algorithm. In case of a weighted round-robin, one can assign a weight to each server in the group so that if one server is capable of handling twice as much load as the other, the powerful server gets a weight of 2. In such cases, the IP sprayer will assign two requests to the powerful server for each request assigned to the weaker one. 

Pros: Takes care of the capacity of the servers in the group.

Cons: Does not consider the advanced load balancing requirements such as processing times for each individual request.

Weighted Round-Robin Allocation

 With this method, the system passes a new connection to the server that has the least number of current connections.

Least Connections methods work best in environments where the servers or other equipment you are load balancing have similar capabilities. 

Least Connections

The Linux Virtual Server is a highly scalable and highly available server built on a cluster of real servers, with the load balancer running on the Linux operating system. The architecture of the server cluster is fully transparent to end users, and the users interact as if it were a single high-performance virtual server. 

Linux Virtual Server

Started in 1998, the Linux Virtual Server (LVS) project combines multiple physical servers into one virtual server, eliminating single points of failure (SPOF).

Built with off-the-shelf components, LVS is already in use in some of the highest-trafficked sites on the Web.

The load balancer, servers, and shared storage are usually connected by a high-speed network to prevent intranet work of the system as cluster grows.

ARCHITECTURE

LVS uses three ways to balance loads :

Virtual Server via NAT (VS/NAT) Virtual Server via Tunneling (VS/TUN) Virtual Server via Direct Routing (VS/DR)

Three Ways To Balance Loads

1. A request packet destined for the virtual IP address arrives at the load balancer.

2. load balancer examines the packet's destination address and port number if match select a real server from the cluster by scheduling algorithm.

3. Request is processed.4. the load balancer rewrites the source address

and port of the packets to those of the virtual service and after termination of connection ,record is removed from hash table.

5. A reply is sent back to the user.

Virtual Server Via NAT (VS/NAT)

VS/NAT Architecture

IP tunneling is a technique to encapsulate IP datagrams with in IP datagrams, which allows datagrams to be wrapped and redirected to another IP address.

This technique can also be used to build a virtual server: the load balancer tunnels the request packets to the different servers, process the requests, and return the results to the clients directly. Thus, the service appears as a VS on a single IP address.

Virtual Server via IP Tunneling (VS/TUN)

VS/TUN Architecture

The load balancer and the real servers must have one of their interfaces.

The virtual IP address is shared by real servers and the load balancer.

In VS/DR, the load balancer directly routes a packet to the selected server.

Receiving of forwarded packet by server it’s address on interface and processes the request, and finally returns the result directly to the user.

Virtual Server Via Direct Routing (VS/DR)

VS/DR Architecture

Wikipediahttp://www.linux-vs.orghttp://www.loadbalancer.orghttp://www.websitegear.com/

REFERENCES

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