Table of Contents
Introduction
About clustered web servers
A clustered web server is a technique used within web hosting to distribute the load across multiple machines or 'nodes'. The aim of this technique is to remove single points of failure and increase website availability and uptime. It is typical that web clusters will utilize multiple backend and frontend nodes.
Clustering doesn't have to be expensive and it's extremely easy to get started with – this guide will demonstrate how to create a round robin two node clustered web server with Nginx and Varnish.
About Varnish
Varnish is a HTTP accelerator; in other words a caching server. It allows us to speed up websites by directing HTTP requests static copy of the website maintained and produced by Varnish.
About Nginx
Nginx is a lightweight, high performance HTTP server that will serve as the backend service to Varnish. It will not directly serve websites to visitors; however, it will respond to requests from Varnish whenever cache is required to be built.
Setup
To perform the steps in this tutorial, you will need three droplets, all of which can be the minimal 512mb instance.
I recommend naming the hostnames of the instances as following:
- varnish
- nginx01
- nginx02
Of course you may add as many "nginx0x" as you wish, but for this tutorial I'll be sticking with 2.
Upon initial SSH into the three newly created instances execute the following command:
sudo apt-get update
Step One - Install Nginx
—
Nginx is the software that will be responsible for serving our website to Varnish.
skip this step for your varnish instance.You must install this on the nginx01 and nginx02 instances, that means repeat this process on each nginx0x server you wish to use.
It is recomended that Nginx is installed from source in order to ensure we get the most up to date version.
Nginx has two major dependencies: PCRE (Perl compatible regular expression library) and zlib (A compression library). At the time of writing this guide, the latest version are:
[Nginx][1]: 1.4.4
[PCRE][2]: 8.34
[zlib][3]: 1.2.8
We must now download the source of the above ready to be extracted and built; enter each of the following commands seperatly:
wget http://nginx.org/download/nginx-1.4.4.tar.gz
wget ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-8.34.tar.gz
wget http://zlib.net/zlib-1.2.8.tar.gz
tar -zxvf nginx-1.4.4.tar.gz
tar -zxvf pcre-8.34.tar.gz
tar -zxvf zlib-1.2.8.tar.gz
Before we go on to build Nginx, we must first obtain a program called "Make" and a compiler for C++ source code 'g++', this will be responsible for carrying out all the commands required to build Nginx on our instances. You may obtain it through apt-get:
sudo apt-get install make g++
At this stage we can now go ahead and build Nginx/ First change directories into the extracted Nginx folder you just created:
cd nginx-1.4.4
Next we must configure the build options for our particular instance:
./configure –with-pcre=../pcre-8.34 –with-zlib=../zlib-1.2.8
Then we can go on to create the Nginx binaries:
make
Finally, we can install Nginx to our system:
sudo make install
Step Two - Install Varnish
—
Varnish will be responsible for serving our website to a visitor.
You must only install this on the varnish instance.
First we need to obtain the GPG Key varnish provides for us to access their repository. We can download it by running the command:
wget http://repo.varnish-cache.org/debian/GPG-key.txt
Then install the key:
sudo apt-key add GPG-key.txt
We then need to add the Varnish repository list to our instances sources list:
echo "deb http://repo.varnish-cache.org/ubuntu/ precise varnish-3.0" | sudo tee -a /etc/apt/sources.list
Then ensure apt-get is aware of Varnish packages:
sudo apt-get update
Finally, install Varnish:
sudo apt-get install varnish
At this stage, we are ready to configure both Nginx and Varnish to serve a website to the outside world!
Step Three - Configure Nginx
—
We don't need to modify the confgurigation of Nginx too much, it's defaults will be fine for this guide. However I recomend we modify the "Welcome to nginx" page we see to specify which VPS is serving the webpage to Varnish.
Navigate to the root html directory where the Nginx welcome page is located:
cd /usr/local/nginx/html/
Now edit index.html:
vim index.html
Modify the file to match the following:
nginx01:
<h1>Welcome to nginx!</h1>
I am nginx01
nginx02:
<h1>Welcome to nginx!</h1>
I am nginx02
Now we can start Nginx (Note: If this command produces no output, it has been executed successfully):
sudo /usr/local/nginx/sbin/nginx
Step Four - Configure Varnish
—
First you must setup Varnish to run on port 80. To do that, you must modify the default Varnish configuration file. First change directories to where this file is located:
cd /etc/default
Then we must open the varnish file:
sudo vim varnish
Locate the following block within the file:
Alternative 2, Configuration with VCL
#
#
DAEMON_OPTS="-a :6081 \
-T localhost:6082 \
-f /etc/varnish/default.vcl \
-S /etc/varnish/secret \
-s malloc,256m"
Modify it to match the following:
Alternative 2, Configuration with VCL
#
#
DAEMON_OPTS="-a :80 \
-T localhost:6082 \
-f /etc/varnish/default.vcl \
-S /etc/varnish/secret \
-s malloc,256m"
Next we need to configure our load balancer. Change directories to where our Varnish configuration script is located:
cd /etc/varnish
Then open the default.vcl file:
sudo vim default.vcl
You must remove the backend default block within this file which looks like the following:
backend default {
.host = "127.0.0.1";
.port = "8080";
}
Replace it with the following. Ensure you change the .host respectivly for nginx01 and nginx02 to your public (or private if your instance has this feature) the cloud provider IP:
backend nginx01 {
.host = "192.168.0.100";
.port = "80";
}
backend nginx02 {
.host = "192.168.0.101";
.port = "80";
}
director nginx round-robin {
{ .backend = nginx01; }
{ .backend = nginx02; }
}
sub vcl_recv {
set req.backend = nginx;
}
Step Five - Test Availability
—
Let's check to see if we can access our website through our Varnish server. Locate the public IP of the varnish instance you started and browser to it through a web browser. If you see the following text, everything is working!
Welcome to nginx!
If you see this page, the nginx web server is successfully installed and working. Further configuration is required.
I am nginx01
For online documentation and support please refer to nginx.org.
Commercial support is available at nginx.com.
Thank you for using nginx.
You can test to see if the site stays online by shutting down Nginx on the server that Nginx reports to be serving from. In my case this was nginx01, to shut down nginx you can execute the following:
/usr/local/nginx/sbin -s stop
Try your Varnish public IP again. You may still see the VPS you just switched off reported as the active server; this is because Varnish is holding the cache. Once this cache expires you will see nginx02 is serving the content.
To force Varnish to clear its cache, restart the service:
sudo service varnish restart
Conclusion
—
At this stage, you now have a fully configured Varnish load balanced round robin cluster. I recomend you follow other tutorials on configuring your Nginx servers further: [How To Install Linux, nginx, MySQL, PHP (LEMP) stack on Ubuntu 12.04][4]
[1]: http://wiki.nginx.org/Install
[2]: http://www.pcre.org/
[3]: http://www.zlib.net/
[4]: https://www.progressiverobot.com/how-to-install-linux-nginx-mysql-php-lemp-stack-on-ubuntu-12-04/
