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  /ftp/web_caching.pdf

Thank you!