Caching Solutions:Varnish

with Bogdan Hadadea

1. General Description: Varnish

• HTTP Accelerator• Caching reverse proxy

o Sits in front of any HTTP server

• Load Balancer• Fail Over System• Perfect Browser caching solution

o Prevents hard refresh calls

• Typical speedup: 300x-1000x• VCL – compiled to C• ESI

1. General Description: Varnish

ESI – Edge Side Includes• Allows page fragmentation• Fragments with different TTL• ESI are serialized• Configurable depth of ESI calls• Doesn’t support alt and noerror attributes• ESI calls can’t set cookies

2. Usage: Varnish

• Originally built for Norwegian newspaper• Current users:

o Facebooko Twittero Huluo BBCo Wired

3. Architecture: Varnish - Overview

3. Architecture: Varnish

Main methods:

• vcl_recv – beginning of request• vcl_fetch – after response from backend• vcl_hash – how to create a hash key• vcl_deliver – before a cached object is delivered• vcl_error – when there is an error

3. Architecture: Varnish

VCL_RECV:

• Manipulate/remove cookies• Manipulate/add/remove headers• Request standardization• Cache bypassing

3. Architecture: Varnish

VCL_FETCH

• Enable ESI• Manipulate headers• Manipulate cookies• Vary• Set/manipulate cache times

4. Comparison: Squid

Advantages of Squid over Varnish:• Built in SSL support• Better support for streaming delivery of objects• Support for antivirus plugins

Advantages of Varnish over Squid:• Amazing configuration system – VCL• Better performance and scalability• Better invalidation support• Better module support

5. Conclusion

• Simple and great performance increase• VCL is powerful but sometimes simple is better• Make sure you can still handle a cold start