Web Caching and Replication

Presented by Bhushan Sonawane

Outline

Introduction Distributed System Relationships Replica Selection Inter-Replica Communication User Agent to Proxy Configuration Inter-Proxy Communication Network Element Communication Security Considerations

Introduction Caching is useful tool in reducing end user latency in the

Web.

Web cache

Monitors object request and stores object as it retrieved from server.

On subsequent request, it will return object request from local storage.

Need to deal with “content freshness” of data. Replication

"Creating and maintaining a duplicate copy of a database or file system on a different computer, typically a server." (From RFC 3040)

Basic Architecture

Distributed System Relationships Replication relationship

Client to Replica Inter-Replica

Proxy relationship

Client to Non-Interception proxy Client to Surrogate to Origin Server(Just like Gateway) Inter-Proxy

Proxy meshes Proxy Arrays

Network Element to Caching Proxy(Switch or Gateway)

Replica Selection Goal

Select optimal replica origin sever Optimality – policy based decision

Network proximity Load

Navigation Hyperlink – Manual selection

Replica HTTP Redirection - “307 Temporary redirect”

DNS redirection – Sort resolved IP addresses based on quality of service policy

Inter-Replica Communication Communication between master-origin and replica-origin

servers for replicating data sets between origin servers.

Batch Driven Replication

Demand Driven Replication

Synchronized Replication

User Agent to Proxy Configuration Manual Proxy Configuration

Proxy Auto Configuration(PAC)

Netscape Navigator, Microsoft Internet Explorer Cache Array Routing Protocol(CARP)

Microsoft Proxy Server, Squid Web Proxy Auto Discovery Protocol(WPAD)

Locate PAC URL Resource Discovery Mechanism

DHCP, SLP, A records

Inter-Proxy Communication Loosely coupled Inter-Proxy Communication

Internet Cache Protocol(ICP) Hyper Text Caching Protocol Cache Digest Cache Pre-filling

Tightly Coupled Inter-Cache Communication

Cache Array Routing Protocol

Network Element Communication

Web Cache Control Protocol(WCCP)

Network Element Control Protocol (NECP)

SOCKS

Security Considerations

Authentication

Man in the middle attacks Trusted third party Authentication based on IP number

Privacy

Trusted third party Logs and legal implications

Security Considerations(Cont..)

Service security

Denial of service Replay attack Stupid configuration of proxies Copyrighted transient copies Application level access

References

HTTP RFC 3040

http://www.ietf.org/rfc/rfc3040.txt http://www.cs.wustl.edu/~jain/cis788-99/ftp/

web_caching.pdf

Thank you!