Knowledgebase

Introduction

Varnish is an open-source HTTP accelerator and reverse proxy designed to increase website and API performance. This article explains how to install Varnish on a cloud server at Rcs and use it to cache frequently accessed content on an Apache web server.

Prerequisites

Before you begin, you need a fully-updated Ubuntu Linux 20.04 server and a sudo user account.

1. Install Apache

1. Update the local package index.

    $ sudo apt update

2. Install Apache.

    $ sudo apt install apache2

3. Configure the firewall to allow traffic.

    $ sudo ufw allow http
    $ sudo ufw allow https

2. Configure Apache

1. Change the default port in Apache from 80 to 8080.

    $ sudo sed -i -e 's/80/8080/g' /etc/apache2/ports.conf
    $ sudo sed -i -e 's/80/8080/g' /etc/apache2/sites-available/*

   > If you add more sites later, you need to change their ports manually in their respective files in the /etc/apache2/sites-available/ directory.

2. Restart Apache.

    $ sudo systemctl restart apache2

3. Verify Apache is listening on port 8080.

    $ sudo netstat -pnlt | grep 8080
   
    Output:
    tcp6       0      0 :::8080                 :::*                    LISTEN      5987/apache2

3. Install Varnish

You must add the official Varnish Cache repository to install the LTS version of Varnish because the default Ubuntu repository has older, unsupported versions.

1. Add the necessary dependencies.

    $ sudo apt install curl gnupg apt-transport-https

2. Install the GPG key for the package.

    $ curl -L https://packagecloud.io/varnishcache/varnish60lts/gpgkey | sudo apt-key add -

3. Add the repository.

    $ echo "deb https://packagecloud.io/varnishcache/varnish60lts/ubuntu/ focal main" | sudo tee -a /etc/apt/sources.list.d/varnish60lts.list

4. Specify a higher priority for this repository than the default package available in Ubuntu.

    $ sudo nano /etc/apt/preferences.d/varnish

5. Add the following content to the file.

    Package: varnish
    Pin: origin packagecloud.io
    Pin-Priority: 900

6. Update the local package index.

    $ sudo apt update

7. Install Varnish.

    $ sudo apt install varnish

4. Configure Varnish

Check the default address and port configuration.

1. Open the default Varnish configuration file.

    $ sudo nano /etc/varnish/default.vcl

2. Verify the backend default section points to localhost (127.0.0.1) at port 8080.

    backend default {
        .host = "127.0.0.1";
        .port = "8080";
    }

3. Save and close the file.

Configure Varnish to listen at port 80 instead of the default of 6081.

1. Create the directory for the custom configuration file.

    $ sudo mkdir /etc/systemd/system/varnish.service.d

2. Create the file.

    $ sudo nano /etc/systemd/system/varnish.service.d/customport.conf

3. Add the following content to the file.

    [Service]
    ExecStart=
    ExecStart=/usr/sbin/varnishd -a :80 -a localhost:8443,PROXY -p feature=+http2 -f /etc/varnish/default.vcl -s malloc,256m

4. Reload systemd to register the change.

    $ sudo systemctl daemon-reload

5. Restart Varnish.

    $ sudo systemctl restart varnish

6. Ensure Varnish is listening on port 80.

    $ sudo netstat -ltnp | grep ':80 '
   
    Output:
    tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      6242/varnishd
    tcp6       0      0 :::80                   :::*                    LISTEN      6242/varnishd

5. Test Varnish

Use curl to make an HTTP request and verify the X-Varnish: 32778 32776 and Via: 1.1 varnish (Varnish/6.0) headers appear in the output.

$ curl -I http://localhost/

Output:
HTTP/1.1 200 OK
Date: Thu, 14 Oct 2021 13:29:54 GMT
Server: Apache/2.4.41 (Ubuntu)
Last-Modified: Thu, 14 Oct 2021 13:25:29 GMT
Vary: Accept-Encoding
Content-Type: text/html
X-Varnish: 32778 32776
Age: 20
Via: 1.1 varnish (Varnish/6.0)
ETag: W/"2aa6-5ce50032ad812-gzip"
Accept-Ranges: bytes
Content-Length: 10918
Connection: keep-alive

Advanced Varnish Settings

How to leverage browser caching for media files

Open the Varnish default.vcl file.

$ sudo nano /etc/varnish/default.vcl

Find sub vcl_backend_response and add the following.

sub vcl_backend_response {
    if (bereq.url ~ "\.(png|gif|jpg|swf|css|js)$") {
        unset beresp.http.set-cookie;
        set beresp.http.cache-control = "max-age = 2592000";
    }
}

This tells the user's browser to cache png, gif, jpg, swf, css, and js files for 30 days.

How to purge the cache

If you need to purge the Varnish cache manually, you can purge the entire cache with:

$ sudo varnishadm 'ban req.url ~ .'

Or, you can purge cache entries for a single domain, such as www.example.com with:

$ sudo varnishadm 'ban req.http.host ~ www.example.com'

Troubleshooting

If curl returns HTTP/1.1 503 Backend fetch failed, check the default.vcl file.

$ sudo nano /etc/varnish/default.vcl

Ensure the backend default section points to Apache at port 8080.

backend default {
    .host = "127.0.0.1";
    .port = "8080";
}

More Information

Varnish is a sophisticated caching proxy with many configuration options beyond the scope of a simple installation guide. Please see the official site and Varnish Users Guide for more information.