High Performance WordPress – Part 5 – Varnish Cache

03 March 2012 comment icon16 | Categories: performance, wordpress

varnish

Boom! At long last the eagerly awaited Part 5 of our High Performance WordPress series sees the light of day!

For those who have not been following along, a quick primer on the other parts in the series:

  • Part 1 – VPS Setup
  • Part 2 – nginx/mysql setup
  • Part 3 – WordPress setup & tuning on nginx
  • Part 4 – APC Opcode Cache install and configuration

First off  I must apologise to those who have been waiting a couple of months for Part 5 to be published. I’ve been exceptionally busy these past few months building themes and only got around to finishing this part in the past 2 weeks. Better late than never I hope!

I’ve also spent the past week or two tweaking and tuning my own VPS which actually back fired a bit the past few days with some outages and sub par performance – kind of ironic for a blog with a whole series on High Performance :) Never the less, it was a very worthwhile experiment which was designed to stretch and tune my varnish config to ensure it is as tight as possible on a low end VPS to ensure you get as much bang for your buck as possible.

What the hell is Varnish Cache?

Quite simply, Varnish Cache is the secret weapon that many of the worlds busiest websites use to supercharge their performance (including WordPress.com! and top WordPress hosts WPEngine). Varnish typically sits in front of your actual web server (in our case nginx but it works equally well with Apache too). Technically Varnish is known as a pure reverse proxy HTTP accelerator. It’s main job is to take the pressure off your web server by caching pages in memory on initial request by a user and then serving these pages directly from virtual memory upon further requests by users so the user never reaches your web server at all. Varnish does a much better job at the simple task of serving http requests as it has been designed from the ground up for exactly this purpose – serving lots of requests for the same content super quickly.

And let me tell you – it is very very fast!

Today we’re going to get you up and running with Varnish sitting in front of your existing nginx powered VPS that we’ve been building up in Parts 1-4 of the series. By the time we’re done you will have what I like to call the Rolls Royce of high perfomance WordPress performance configurations :)

Install Varnish

Alright let’s dive in. Step 1 is the install of Varnish itself. To ensure we’re getting the latest and greatest version of Varnish for Ubuntu 10.10 we’ll grab the Varnish version provided by varnish-cache.org directly as follows.

First, ensure you have curl installed if you don’t already:

apt-get install curl

Then let’s get on with the Varnish install

curl http://repo.varnish-cache.org/debian/GPG-key.txt | apt-key add -
echo "deb http://repo.varnish-cache.org/ubuntu/ lucid varnish-3.0" >> /etc/apt/sources.list
apt-get update
apt-get install varnish

As of the time of writing this should get you Varnish 2.1.3 on Ubuntu 10.10. (You can check this by running

varnishd -V
varnishd (varnish-2.1.3 SVN )
Copyright (c) 2006-2009 Linpro AS / Verdens Gang AS

Switch Varnish to Port 80 and nginx to Port 8080

Seeing as we want Varnish to sit in front of nginx we will need to switch Varnish over to port 80 so it intercepts all http requests first. Right now nginx is serving our WordPress website via the standard http port – port 80. As a result, we’ll need to reconfigure nginx to listen on a different port. We’re going to switch nginx to listen on Port 8080 and Varnish will pass requests to it based on the policies with define within Varnish. Thankfully Varnish comes with a very flexible and easy to configure language called VCL. VCL enables you to write policies about how incoming requests should be handled. Let’s switch ports.

By default, Varnish listens on port 6081, we’ll switch to 80. Find this codeblock in:

nano /etc/default/varnish
## Alternative 2, Configuration with VCL
#
# Listen on port 6081, administration on localhost:6082, and forward to
# one content server selected by the vcl file, based on the request.  Use a 1GB
# fixed-size cache file.
#
DAEMON_OPTS="-a :6081 \
-T localhost:6082 \
-f /etc/varnish/default.vcl \
-S /etc/varnish/secret \
-s file,/var/lib/varnish/$INSTANCE/varnish_storage.bin,1G"

and replace port 6081 with 80

## Alternative 2, Configuration with VCL
#
# Listen on port 80, administration on localhost:6082, and forward to
# one content server selected by the vcl file, based on the request.  Use a 96M
# fixed-size cache file.
#
DAEMON_OPTS="-a :80 \
-T localhost:6082 \
-f /etc/varnish/default.vcl \
-S /etc/varnish/secret \
-s file,/var/lib/varnish/$INSTANCE/varnish_storage.bin,96M"

There is another really important change we made on the last line above. We adjusted the virtual memory allocation for Varnish from 1GB down to 96MB. Why the change? Well I’m assuming that you are running the a low end VPS with maybe 512MB of RAM. If so, you don’t want Varnish consuming too much memory and pushing you into swap file disk thrashing. Keep it low to start with and adjust upwards if necessary. The “varnishstat” command will provide you with all sorts of useful information about how your cache is performing.

The other change you will want to make in this file is to ensure varnishd is set to start at boot

# Should we start varnishd at boot? Set to "yes" to enable.
START=yes

Before starting Varnish, we need to switch nginx to Port 8080. Let’s do that now:

nano /etc/nginx/sites-enabled/engine.ex.conf  (or whatever your config file is called)

In your server block switch the listen port from 80 to 8080.

listen   80; ## listen for ipv4; this line is default and implied

becomes

listen   8080; ## listen for ipv4; this line is default and implied

At this point let’s restart nginx and varnish

service nginx restart
service varnish restart

Now when you run a simple netstat you should see Varnish on Port 80 and nginx on 8080:

netstat -anp --tcp --udp | grep LISTEN

Something like this:

tcp6       0      0 :::80                   :::*                    LISTEN      30464/varnishd
tcp        0      0 0.0.0.0:8080            0.0.0.0:*               LISTEN      30099/nginx

Now it’s time to optimise Varnish to play nice with WordPress!

Optimise your Varnish Config for WordPress

Now it’s time to tune for default VCL to play nice with WordPress. For now let’s go ahead and do that and afterwards we’ll touch on a few key points about this config.

nano /etc/varnish/default.vcl
# This is a basic VCL configuration file for varnish.  See the vcl(7)
# man page for details on VCL syntax and semantics.
#
# Default backend definition.  Set this to point to your content
# server.
#
backend default {
.host = "127.0.0.1";
.port = "8080";
}
acl purge {
"127.0.0.1";
}
sub vcl_recv {
# Add a unique header containing the client address
remove req.http.X-Forwarded-For;
set    req.http.X-Forwarded-For = client.ip;
# Let's make sure we aren't compressing already compressed formats.
if (req.http.Accept-Encoding) {
if (req.url ~ "\.(jpg|png|gif|gz|tgz|bz2|mp3|mp4|m4v)(\?.*|)$") {
remove req.http.Accept-Encoding;
} elsif (req.http.Accept-Encoding ~ "gzip") {
set req.http.Accept-Encoding = "gzip";
} elsif (req.http.Accept-Encoding ~ "deflate") {
set req.http.Accept-Encoding = "deflate";
} else {
remove req.http.Accept-Encoding;
}
}
if (req.request == "PURGE") {
if (!client.ip ~ purge) {
error 405 "Not allowed.";
}
return(lookup);
}
if (req.url ~ "^/$") {
unset req.http.cookie;
}
}
sub vcl_hit {
if (req.request == "PURGE") {
set obj.ttl = 0s;
error 200 "Purged.";
}
}
sub vcl_miss {
if (req.request == "PURGE") {
error 404 "Not in cache.";
}
if (!(req.url ~ "wp-(login|admin)")) {
unset req.http.cookie;
}
if (req.url ~ "^/[^?]+.(jpeg|jpg|png|gif|ico|js|css|txt|gz|zip|lzma|bz2|tgz|tbz|html|htm)(\?.|)$") {
unset req.http.cookie;
set req.url = regsub(req.url, "\?.$", "");
}
if (req.url ~ "^/$") {
unset req.http.cookie;
}
}
sub vcl_fetch {
if (req.url ~ "^/$") {
unset beresp.http.set-cookie;
}
if (!(req.url ~ "wp-(login|admin)")) {
unset beresp.http.set-cookie;
}
}

Ok so what the frick is this all about?

The VCL file above mainly comes from here where it is explained very well exactly what is going on. I’ve made a few minor adjustments over the past 9 or 10 months that I’ve been running it here on themesforge – but it’s working pretty damn well. A few important points to note:

  • By default, Varnish will not cache any requests where cookies are being transmitted. WordPress has quite a lot of cookie action. For most blogs, these are insignificant and we can safely drop these in favour of serving content from Varnish cache rather than directly by the webserver – hence the numerous calls to “unset beresp.http.set-cookie;” above.
  • There are some notable exceptions where we absolutely don’t want to drop cookies, including logins and admin access, hence the exceptions provided by the “if (!(req.url ~ “wp-(login|admin)”)) {” call.
  • Our config will also bust the Varnish cache when a new blog post is published.
  • Another important call is the “set    req.http.X-Forwarded-For = client.ip;” call which ensures that the users IP address is passed to nginx – otherwise your nginx web logs will be full of localhost/127.0.0.1 entries – which are useless to us! This is also the reason that we installed the “nginx-extras” package back in Part 2 so we could avail of the nginx Real IP module which is not enabled by default in the default package (I know crazy!)

Save your config file and give Varnish and nginx one last restart to reload their configs:

service nginx restart
service varnish restart

And with that your VPS is now super charged and ready for bucketloads of traffic!

How do I know if my Varnish config is performing correctly?

Varnish comes with some really useful diagnostics. First, I’m assuming you ran the netstat earlier to ensure Varnish and nginx are on the correct ports right?

Ok, here’s some useful tips for making sure Varnish is actually working.

varnishstat

Varnishstat displays a wealth of information about how Varnish is performing, some key values to look out for:

  • Hitrate Ratio and Hitrate avg: These numbers represent Varnish’s pulse. Right now my ratios are 10, 100, 181 which corresponds to numbers of seconds. Under each of these values, you will see a decimal value – something like  0.9843 – multiply this number by 100 and you have the percentage of your http requests which are being served by Varnish – i.e. cache hits. When you first launch Varnish you can expect your hitrate percentages to be very low but should dramatically increase once you start pointing traffic at your site.
  • Cache Hits – You will want to see this number climbing rapidly as you point traffic to the frontend.
  • Cache Misses – At first launch and as users first request new pages this number will increment.
  • N LRU nuked objects – This number should be zero – if it starts incrementing then it’s time to increase the size of virtual memory assigned to varnish. This number is basically a count of the number of cache objects that had to be removed to make room for new objects.

This is only really scratching the surface of what varnishstat can tell you. You can find out more about varnishstat here.

Other useful varnish commands that I use frequently:

varnishtop -i rxurl – will show you what URLs are beeing asked for by the client

varnishtop -i RxHeader -I Accept-Encoding will show the most popular Accept-Encoding header

Conclusion – what now?

So that’s it fot the High Performance WordPress blog post series for now. If you’ve followed along from the beginning you are now in possession of a finely tuned speed optimised platform for hosting your WordPress websites. That said, the pace of innovation in this space is incredible and constantly changing (for the better). We’ve only really scratched the surface of many highly complex subjects and you should continue to learn about how to tune your own specific server environment. We’ll be coming back to this series later in the year. For now, if you don’t have the time to build out your own servers and would like some assistance we plan on offering a server deployment service in the near future where we roll out finely tuned VPS machines based on your specific needs. Drop me a line if you’re interested.

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16 Responses to “High Performance WordPress – Part 5 – Varnish Cache”

  1. Hrvoje on 3 March 2012 at 12:04 pm said: Permalink

    Finally, I’ve been waiting for this part for tooo long :-).
    Does this vcl configuration works and behave nice with wp multisite installs or does it needs something extra to configure? Have You tried it on multisite?

    • Ed on 3 March 2012 at 1:55 pm said: Permalink

      Hey Hrvoje – yes I’ve even been waiting for it for too long :)

      I’ve not tested this config with multi-site to be honest – I wouldn’t expect that would have any problems though as long as your nginx config works with multi-site.

      There is an alternative VCL config over here that confirms multi-site support just in case you do run into problems.

      http://mclear.co.uk/2011/10/05/wordpress-varnish-cache-config-vcl/

      I’ve looked through that config and it’s pretty sweet.

      Ed

      • Hrvoje on 4 March 2012 at 5:31 pm said: Permalink

        I’m planning on launching multisite for my next project, so I’ll need something like this.
        Tnx!

    • Ed on 3 March 2012 at 1:55 pm said: Permalink

      Hey Hrvoje – yes I’ve even been waiting for it for too long :)

      I’ve not tested this config with multi-site to be honest – I wouldn’t expect that would have any problems though as long as your nginx config works with multi-site.

      There is an alternative VCL config over here that confirms multi-site support just in case you do run into problems.

      http://mclear.co.uk/2011/10/05/wordpress-varnish-cache-config-vcl/

      I’ve looked through that config and it’s pretty sweet.

      Ed

  2. Pothi Kalimuthu on 13 March 2012 at 7:35 am said: Permalink

    Thanks for another great write up on performance.

    A typo on h3 heading entitled “Switch Varnish to Port 80 and nginx to Port 8082″. It should’ve been “Switch Varnish to Port 80 and nginx to Port 8080″

    Personally, I’d recommend keeping Nginx in port 80 and Varnish on its default port (6081). Because, if I’m in a situation where I have to tweak something in Varnish, I have to kill varnishd process and then start it again with the modified configuration file. In this situation, if Nginx is at port 80, I can temporarily switch the traffic directly to Apache (or to PHP-FPM) while Varnish is being tweaked.

    On the other hand, if I have to tweak something with Nginx, it offers an easy way to reload the configuration file without affecting the visitors flow.

    Pothi

  3. Danny Dang on 22 April 2012 at 1:00 am said: Permalink

    I think I may have missed a step.. but after swapping listening ports, I now only get the Welcome to nginx! page and wordpress is not serving. If I swap it back, site comes back. Any ideas?

    • Marc on 6 May 2012 at 6:58 pm said: Permalink

      Same problem here! after my changes in the nginx.conf of the site, nginx still listens to Port 80. Don’t know where to change nginx conpletely from listening to port 80.

      • Ed on 6 May 2012 at 10:53 pm said: Permalink

        Hi Marc,

        You should double check your main nginx.conf file in:
        /etc/nginx/nginx.conf

        You may have another server listen directive in there listening on port 80. If so, change it to 8080 and restart nginx again..

        Ed

    • Marc on 6 May 2012 at 7:00 pm said: Permalink

      That line in NETstats is bothering me:
      tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 5726/ nginx

  4. Jon on 13 July 2012 at 2:37 am said: Permalink

    Thank you and WP Mayor for posting this 5-part VPS tutorial! Happy to announce that after a late night of going through all five parts that my website is stable and blazing fast…

    After adding Varnish with the above config. I’m noticing two “bugs.” The first is that my homepage doesn’t recognize that I’m logged in as admin. The admin bar is missing until I go to another page on the website. If I go back to the homepage, the admin bar disappears. Do you encounter anything similar with your config.

    The second is that none of the lightbox frames created via WP plugin Easy FancyBox open. Regardless of the media file or how they’re linked or embedded, clicking won’t even open the link in a new tab or window. I have to right click and open in a new window just to view it.

    There must be a way to configure the vcl in order to avoid these errors. Overall though, this VPS tutorial series has been amazing! Thank you for your help!

  5. Darius on 20 December 2012 at 3:32 pm said: Permalink

    Hello there,

    I cannot get the WordPress and W3 to clear Varnish cache on new post.

  6. Ryan on 28 December 2012 at 8:10 am said: Permalink

    I don’t get how people are able to set up their box using this 5 part guide. I’ve been rebuilding my server for 6 to 8 times now. I can’t figure it out.

    There’s some things that are simply glossed over. And some are even outdated i believe. For example, PHPMyadmin, should i choose “yes” for something called dbconfig? I have no idea.

    Another thing is that default nginx file is not nginx/www/ but nginx/html i believe. That’s because there’s no “www” folder. It took me a long frustrating night to realize maybe the guide is outdated.

    I hope the guide can be clarified and updated. Thanks

    • Ed on 2 January 2013 at 12:23 pm said: Permalink

      Hey Ryan,

      It’s a little outdated now seeing as it’s 9 months since the last part was written and nginx releases are very frequent. (things move very fast in the nginx world). Yes some parts have changed (like the nginx default web root at install) but I just used my own tut so rig up a new vps over Christmas so it’s still pretty relevant :)

      Re: glossing over – I think it goes to a pretty deep level – but some experience with unix/linux sys. admin does help. I would love to dedicate more time to do more in-depth tutorials (with video) but time is very scarce these days.

      I do offer professional server setup as a service if you need assistance – just let me know.

      Ed

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