Varnish

Varnish, as mentioned on its official website, makes your website fly; and this is true! Varnish is an open source web application accelerator that runs in front of your web server software. It has to be configured on port 80 so that each request comes to it.

Now, the Varnish configuration file (called VCL files with the .vcl extenstion) has a definition for backends. A backend is the web server (Apache or NGINX) configured on another port (let's say 8080). Multiple backends can be defined, and Varnish will take care of the load balancing too.

When a request comes to Varnish, it checks whether the data for this request in available at its cache or not. If it finds the data in its cache, this cached data is returned to the request, and no request is sent to the web server or backend. If Varnish does not find any data in its cache, it sends a request to the web server and requests the data. When it receives data from the web server, it first caches this data and then sends it back to the request.

As it is clear in the preceding discussion, if Varnish finds the data in the cache, there is no need for a request to the web server and, therefore, for processing in there, and the response is sent back very fast.

Varnish also provides features such as load balancing and health checks. Also, Varnish has no support for SSL and cookies. If Varnish receives cookies from the web server or backend, this page is not cached. There are different ways to overcome these issues easily.

We've done enough theory; now, let's install Varnish on a Debian/Ubuntu server via the following steps:

First, add the Varnish repositories to the sources.list file. Place the following line in the file:
```
    deb https://repo.varnish-cache.org/debian/ Jessie varnish-4.1
```
After this, issue the following command to update the repositories:
```
sudo apt-get update
```
Now, issue the following command:
```
sudo apt-get install varnish
```
This will download and install Varnish. Now, the first thing to do is configure Varnish to listen at port 80 and make your web server listen at another port, such as 8080. We will configure it here with NGINX.

Now, open the Varnish configuration file location at /etc/default/varnish and change it so that it looks similar to the following code:

    DAEMON_OPS="-a :80 \
      -T localhost:6082 \ 
      -f /etc/varnish/default.vcl \
      -S /etc/varnish/secret \
      -s malloc,256m"

Save the file and restart Varnish by issuing the following command in the terminal:
```
sudo service varnish restart
```
Now our Varnish runs on port 80. Let's make NGINX run on port 8080. Edit the NGINX vhost file for the application and change the listen port from 80 to 8080, as follows:
```
    listen 8080;
```
Now, restart NGINX by issuing the following command in the terminal:
```
sudo service nginx restart
```
The next step is to configure the Varnish VCL file and add a backend that will communicate with our backend on port 8080. Edit the Varnish VCL file located at /etc/varnish/default.vcl, as follows:
```
    backend default {
      .host = "127.0.0.1";
      .port = "8080";
    }
```

In the preceding configuration, our backend host is located at the same server on which Varnish runs, so we entered the local IP. We can also enter a localhost in this case. However, if our backend runs on a remote host or another server, the IP of this server should be entered.

Now, we are done with Varnish and web server configuration. Restart both Varnish and NGINX. Open your browser and enter the IP or hostname of the server. The first response may seem slow, which is because Varnish is fetching data from the backend and then caching it, but other subsequent responses will be extremely fast, as Varnish cached them and is now sending back the cached data without communicating with the backend.

Varnish provides a tool in which we can easily monitor the Varnish cache status. It is a real-time tool and updates its contents in real time. It is called varnishstat. To start varnishstat, just issue the following command in the terminal:

varnishstat

The preceding command will display a session similar to the following screenshot:

As can be seen in the preceding screenshot, it displays very useful information, such as the running time and the number of requests made at the beginning, cache hits, cache misses, all backends, backend reusages, and so on. We can use this information to tune Varnish for its best performance.

Note

A complete Varnish configuration is out of the scope of this book, but a good documentation can be found on the Varnish official website at https://www.varnish-cache.org.

Table of Contents for PHP 7: Real World Application Development

Varnish

Note

Table of Contents for
PHP 7: Real World Application Development