Implementing a Load-balanced Web Server System

Architecture of A Cluster-based Web System

Courtesy: IBM Research Report, The state of the art in the locally distributed Web Server systems.

Architecture of Our Web Server Cluster

Web Server 1

File Service

Database Service

Web Server 2

File Service

Video-On-Demand

Load Distributor

(grid1.cs.ucr.edu)

http requests

http

req

uest

s

Our Web Server Cluster

The whole web server only provides one visible web address to the outside world.

Each Web Server is able to provide two kinds of web services.

The load distributor distributes the incoming requests among the servers according to either content-aware or content-unaware load balancing strategies.

Tasks to do to set up the system

Building up the web services on the servers File Services Video-on-demand Services Database Services

Implementing the load distributor on the frond-end node Content aware request distribution Content unaware request distribution

Building Up the Web Services

File service Built on top of Apache server. File set is generated by SPECWEB99.

Video-On-Demand Real MPEG2 movies are stored in a specific directory

on the Apache server. Client video streaming software (VideoLan) is installed

and automatically launched by the Apache server.

Database service Built on top of Apache and MySQL.

Video On Demand Service

VideoLAN project (Open Source Media Streaming Solution)

Targeting multimedia streaming of MPEG-1, MPEG-2, MPEG-4 and DivX files, DVDs, digital satellite channels, digital terrestial television channels and live videos on a high-bandwidth IPv4 or IPv6 network in unicast or multicast.

Client-server Architecture Server streams MPEG-1, MPEG-2 and MPEG-4 / DivX

files, DVDs and live videos on the network in unicast or multicast.

Client receives, decodes and displays MPEG stream.

VideoLan System

Building Up Video-On-Demand Service in Our Web Server

VideoLan client-server software is installed

Server can stream movies to the client in realtime through UDP/RTP or HTTP/TCP

For video-on-demand service using HTTP/TCP, only the client is needed. The client software (vlc) is automatically launched once the Apache server detects that it is a video file.

Load Balancing Schemes

Content Unaware Scheme Choose a server before receiving the URL

request Round Robin

Content Aware Schemes Choose a server to dispatch a request after

receiving and looking at the URL request Balance load according to different URL

request For database service — Database Server For video-on-demand service — Multimedia Server For file service — Round Robin

Implementing the Load Distributor

Install the TCPSP The tcp splicing is a technique to splice two connections

inside the kernel, so that data relaying between the two connections can be run at near router speeds.

Write the Distributor program in C language Two load balancing strategies are implemented The installed kernel module TCPSP is invoked to

perform TCP splicing

Run the distributor program in the application level

Flow Chart of the Load Distributor(content aware)

Establish a TCP connection with the

chosen serverSplice two TCP connections

End

Write the URL request to the second TCP connection

Monitor the two TCP connections and close them when no more activities are

going on

Distributor

Child Process

Listen for incoming connections on port

8888

Accept the connection

Choose a server according to the request type and load balancing

scheme

Create a child process to do further processing

Read the URL request

Flow Chart of the Load Distributor(content unaware)

Establish a TCP connection with the

chosen server

Listen for incoming connections on port

8888

Accept the connection

Choose a server according to the load

balancing scheme

Create a child process to do further processing

End

Splice two TCP connections

Read the URL request

Write the URL request to the second TCP connection

Monitor the two TCP connections and close them when no more activities are

going on

Distributor

Child Process

Comparison with Gage

Gage : A QoS Aware Web Server System “Performance Guarantees for Cluster-Based

Internet Services”, Chang Li, State University of New York at Stony Brook.

The load distributor is implemented as a kernel module. It is faster but can only implement content-unaware load balancing.

Gage doesn’t provide a variety of web services.

Planned Performance Measurement

Let all servers provide file service, use SPECWEB99 to test the performance of the cluster-based file server.

Compare the time taken to service a Database request through the load distributor with that without the load distributor.

Compare the time taken to service a Database request through the load distributor with that without the load distributor.

SPECWEB99

Let’s go to the lab to see DEMO!