Ergonet Varnish Cache

WordPress plugin for automating Varnish purge on articles and pages. This plugin is designed to work on Ergonet hosting services.

ERGONET VARNISH CACHE FOR WORDPRESS

Ergonet Varnish Cache is a free plugin developed by Ergonet srl, an Italian hosting company, to improve performance of a website developed in WordPress.

BENEFITS

Using a reverse proxy system based on Varnish web accelerator will increase performance of your WordPress site starting from a minimum of 30% to a maximum of 60%. Remember that the performance improvement will also depend on the entire optimization strategy of your website.

WHAT IS VARNISH?

Varnish is an http accelerator (also called reverse proxy) that saves entire WordPress sites pages on RAM memory, the fastest storage available, returning them immediately to the website visitor.
Therefore, if a specific page of your site has already been visited previously and is available in cache, Varnish will immediately return it to the user who is requesting it, without requesting its generation again from your WordPress site.
If a visitor visits a page not yet in cache, Varnish will request it directly to Apache / NGINX web server, adding it to cache to speed up next requests of the same resource.

COMPATIBILITY

Ergonet Varnish Cache is fully compatible with all other caching and website optimization plugins. For example WP Rocket, Autoptimize, W3 Total Cache, WP Fastest Cache and so on. However it’s recommended to disable the Page caching option of these plugins, because, besides being less performing then Varnish, may lead to incompatibilities.
Ergonet Varnish Cache plugin works as a communication layer between WordPress and Varnish caching system installed on Ergonets hosting platform. Varnish is available on shared hosting plans with “Successo” performance profile and dedicated Cloud Hosting (Solo and Multidominio) available for purchase on https://www.ergonet.it
A fundamental requirement for the operation of the plugin is the activation of Varnish cache system from WebPanel (Ergonet customers area available at https://webpanel.ergonet.it) by the user who purchased hosting service.

HOW PLUGIN WORKS

Once Varnish cache system is activated from Ergonets WebPanel and Ergonet Varnish Cache plugin is installed and activated, it will work without any additional configuration.

Caching resources
A resource, intended as an URL, will be automatically added into Varnish cache when an anonymous user visits the page.

Updating cached resources
Whenever the webmaster updates an article or page, the plugin will take care of deleting the old resource in the cache, to prevent users from viewing old content.
At the same time, homepage cache will also be deleted and updated with last articles.

Clearing Cached Resources
Given the automatic update and removal of resources, there will be no need to forcibly clear cache. Furthermore, total cache deletion is a not recommended action, as it would delete all resources (pages, articles, etc.) that have been stored previously since they were heavily visited.
On sites with a lot of content, total cache deletion could also cause a significant slowdown, due to the need to regenerate from scratch all WordPress pages or articles requested by users.

WHAT WILL NOT BE CACHED

To make Varnish caching system efficient, there are some specific resources and HTTP calls that will never be cached:

• Any page, article / resource visited by a logged in user.
• Any page, article / resource with no-cache header set.
• All WordPress backend calls.
• All calls made for data entry (registration form, contacts, comments and so on).

HOW TO CHECK THAT VARNISH CACHE IS WORKING

Varnish caching system sets specific headers if the called resource (link) is available or not in cache. To check if website is using Varnish cache, it is therefore necessary to check for the presence of specific Varnish headers.

Open your browser developer:

Firefox: tools->web development->Activate tools.
Chrome: View->development options->developer tools

Now, on developer tools:
* select “Network” tab
* select “HTML” sub tab in Firefox or “Doc” in Chrome
* refresh your page
* click on the domain name row identified by 200 status code

The response headers will open in the right column, last header will be the one related to Varnish:

X-VC-Cache: HIT = the resource, therefore the page called, is available in cache and has been returned by Varnish. It means that the cache system is working properly.

X-VC-Cache: MISS = the resource, therefore the page called, is NOT available in cache and was generated by WordPress application. It means that the cache system has been instructed by the application headers or by custom rules, not to return the content from cache.

ACTIVATION OF VARNISH CACHE SYSTEM FROM WEBPANEL

From Ergonets WebPanel additional Varnish configurations are available:

Cache expire
Recommended configuration: 1 week
Time retention of a given resource in cache. After this time, the resources available in Varnish cache that have reached this retention period will be deleted.
Remember that a resource (for example a page or an article), if modified or updated, will be deleted from the default cache, without considering its validity time and without the need to clear the entire cache. Whenever you update a page or article, homepage cache will also be invalidated.

Force cache
Recommended configuration: OFF
Some plugins or themes forces Cache Control headers to not allow Varnish to cache a resource. It is always preferable not to force this directive, as the headers are expected to be correctly set by applications, themes and plugins developers.
If activated, carefully check that there are no unexpected issues on website.

Dedicated memory (option only available on dedicated Cloud Hosting)
Recommended configuration: 128MB
Amount of RAM memory assigned to Varnish cache; 128MB is enough for most websites. For portals or e-commerces with a lot of content or products, we suggest setting it to 256MB or 512MB.
Keep in mind that the more RAM you will assign to Varnish, the less it will remain available for all other websites hosted on the same server and for the operating system. Increase the amount of Varnish RAM only if you have enough memory available.

Terms to exclude
Terms and words that if found on URLs should exclude content from being cached. There are already some default terms, but the list can be enriched if necessary by the user.