1 Distributed Systems : Server Load Balancing Dr. Sunny Jeong. Mr. Colin Zhang With Thanks to Prof. G. Coulouris, Prof. A.S. Tanenbaum

2 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 4

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 Switching Reading the cookie information to solve the Mega 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 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 10

Dynamic load balancing React based on servers status and the request from client  Least connection  Fastest response  Least loaded (SNMP agent) 11

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 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 load_balancing.html# Other references on load balancing from [2] Load Balancing Servers,Firewalls, and Caches by Chandra Kopparapu S.Mathialagan Georgia State University IBM Technical Report