Varnish Cache - Initial cache of web pages

2
votes

I have installed the Varnish cache with my Apache web server and configured them correctly. It works OK and I can now access my web pages though Varnish Cache.

The default behavior of varnish is to store copies of the pages served by the web server. The next time the same page is requested, Varnish will serve the copy instead of requesting the page from the Apache server.

And now comes my question: Is it possible to cache my entire website initially after setting up the Varnish cache, without the need to have a page to be accessed then store it on the cache? This is because, after varnish has been setup, the cache is initially empty, and it will require a page to be accessed in order to be available on the cache. Can this be done without having to access each page manually?

2
apachecachingvarnishvarnish-vcl

2 Answers

4
votes

What you are looking for is a way of warming up the cache. You could use varnishreplay or a Web crawler, such as Wget or HTTrack to go through your site. Alternatively if you have a sitemap of your pages you could use that as a starting point and warm up the cache by looping over it and issuing requests on the pages using e.g. curl or wget.

Using varnishreplay requires you to first run varnishlog and gather a log of traffic before you can use it later for playing back the traffic and warming up the cache.

Wget, HTTrack etc. can be pointed to your home page and they will crawl their way through your site. Depending on the size and nature of your site this might not be practical though (for example if you use Ajax extensively).

Unless your pages take a very long time to load from the backend server (i.e. Apache), I wouldn't worry too much about warming up the cache. If the TTL for the cached content is high enough most of the visitors will only ever receive cached content anyway.

1
votes

There is a much better way to do this which employs req.hash_always_miss and works with Varnish 3 and 4 (employs sitemap too). It warms up your cache and refreshes old pages without having to purge the cache. Full diagram, outline of how to configure it and 3 scripts for various use cases are outlined here http://www.htpcguides.com/smart-warm-up-your-wordpress-varnish-cache-scripts/ and are easily adapted for non-Wordpress sites.