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Distributed Systems : Server Load Balancing
Dr. Sunny Jeong. [email protected]. Colin Zhang [email protected] Thanks to Prof. G. Coulouris, Prof. A.S. Tanenbaum
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Overview
Server load balancing
Introduction
Basic concepts
Static load balancing
Dynamic load balancing Load balancing in Java
Introduction
In computer networking, load balancing is a technique to distributed work between many computers, processes, hard disks or other resources in order to get optimal resource utilization and decrease computing time [3].
The function is performed by the load balancers.
Introduction – Understanding the Load Balancer
Server with a load balancer
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Introduction – Understanding the Load Balancer
An easy example – Router in a call center server
Load Balancer – Software & hardware
Various other functions like • Server load balancing
• Firewall load balancing • Transparent cache switching • Server protection• Fault Tolerance
Load Balancer does not works in the application level
Advanced Concepts
Session Persistence
The mega proxy problem
Delayed binding
Cookie switching
Advanced Concepts - Session Persistence
How application that runs on top of TCP/IP protocol affects the function of load balancer –
Advanced Concepts – the mega proxy problem
Situations where the source IP is not a reliable way to identify a user, due to a proxy server is known as the megaproxy problem
Advanced Concepts
Delayed Binding Delayed binding is this process of delaying the binding of a TCP connection to a server until after the application request is received.
Cookie SwitchingReading the cookie information to solve theMega proxy problem
Static load balancing
No consideration of servers and network states, conducting based on preprogrammed server manuals
Round Robin Server instances called in order Simple and cheap are the advantages If one is slow others will be affected Note: not suitable FTP server (Persistency)
Weight based load balancing Weighted in scale of 1-100 depending on the load managed by
server Load distributed accordingly
Priority Group Activation Use only active server Stand by server active in needed time only Easy to maintain
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Dynamic load balancing
React based on servers status and the request from client
Least connection Fastest response Least loaded (SNMP agent)
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Application - Global Server Load Balancing
Domain Naming Service
Positioning the GSLB• Not to affect the existing flow• Site selection
Application - GSLB
Site selection based on the following [2] Site health conditions Site response time Site Loading time
Application – Web Caching
Caches can be installed and utilized with the Load balancers in the following ways [2] Forward proxy for client acceleration Transparent proxy for client acceleration Reverse proxy for server acceleration Transparent reverse proxy for server acceleration
Application – Web Caching
Transparent reverse proxy for server acceleration
Load Balancing in Java
Load Balancing for Servlets and JSPs
Load Balancing for EJBs and RMI Objects
Load Balancing for JDBC Connections
Load balancing in Java – Servlets and JSPs
Load Balancing with a Proxy Plug-in Weblogic proxy plug-in maintains as list of web logic
servlet and JSP instances
Forwards the HTTP request to those cached instances in round-robin method
Some webservers and associated proxies Weblogic server & HTTPClusterServlet Apache with Apache proxy plug-ins Microsoft IIS with IIS plugins
Load balancing in Java – EJB’s and RMI’s
The Object instances stored in the stubs
Techniques Round Robin Load Balancing Weight-Based Load Balancing Random Load Balancing
Load balancing in Java – EJB’s and RMI’s
Round Robin Load Balancing Server instances called in order Simple and cheap are the advantages If one is slow others will be affected
Weight based load balancing Weighted in scale of 1-100 depending on the load managed by
server Load distributed accordingly
Random Load Balancing Does not discrete difference in processing and assumes
homogenous systems Overhead in generating random number simple
Load balancing in Java – JDBC Connection
Load balancing of JDBC connection requires the use of a multipool configured for load balancing. Load balancing support is an option you can choose when configuring a multipool
Multipool has an ordered lit of connection pool that routes the connection
Default the first connection pool if not run in load balancing mode
References
Load Balancing in Java
http://e-docs.bea.com/wls/docs81/cluster/load_balancing.html#1043771
Other references on load balancing from [2]
Load Balancing Servers,Firewalls, and Caches by Chandra Kopparapu
S.Mathialagan Georgia State University
IBM Technical Report