Life in today’s world is majorly dependent on computers. There is simply a minimal chance of our day passing by without web surfing. Be it a small scale establishment or a huge organization, websites play a key role in the growth of any business. A website becomes the backbone that showcases your business presence on a wider scale across the world. However, it is a bitter truth that most of the websites fail to seize the expected targeted audience. One of the crucial reasons for this fall back is the website performance. A normal customer usually does not wait for more than 3 seconds before abandoning a website.


There are many factors that help to increase the performance of any website. Website Caching is one of the most beneficial technologies that work to enhance the website’s performance which in turn leads to better SEO scores and increased user satisfaction. Website Caching helps the server to store the regularly accessed dynamic content in its Random Access Memory. This reduces the load on the server as it does not need to regenerate the same content from the scratch and just transfer it from the RAM every time it’s accessed.

What is Varnish Cache?

Varnish Cache (VC) is one of the best caching solutions that greatly assist to maximise the speed of your business web applications. It is a front-end web applicator that permits dynamic and large content websites to effectively handle the spike in web traffic.

It is a reverse caching HTTP proxy that has the capability to cache both static and dynamic content from the server and accelerate the website’s user experience. In other words, VC simply acts as a middleman between the client and the web server.

Once a website receives a request for the first time, Varnish will transfer it to the webserver for an appropriate output. This output from the server will be cached in Varnish before redirecting it to the client. Any subsequent request for the same content will be directed to Varnish instead of routing to the server. With Varnish Cache in place, the web application will be able to handle multiple requests from several users and the server will not even get started.

This eventually leads to a magical rise in the performance of the web application. Varnish Configuration Language (VCL) allows performing modifications to Varnish‘s normal behaviour by including new logic to manipulate requests. It also permits modifying the response coming back from the web server, eliminates cookies or includes header responses.

Varnish Cache WordPress

One of the most well-known Open Source Content Management Systems is the WordPress Website. Varnish Cache is the best caching solution that can be implemented on a WordPress website. Depending on the amount of traffic and the complexity of the website VC helps to overcome the performance lags that exist in the website. The Varnish is very easy to implement and use in a WordPress Website. A WordPress Website supports both Varnish 3 and Varnish 4 caches. But it is always recommended to implement the latest version.

Once installed, the WordPress website can be instructed to interact and purge Varnish Cache if the cached content gets changed. One of the most commonly used plugin by the WordPress to purge Varnish Cache is Varnish HTTP Purge plugin.

Varnish HTTP Purge

Varnish HTTP Purge is unique and has more advanced features when compared with similar other plugins. The contents in Varnish don’t actually get saved to the cache, but it allows purging of the current cache. As this plugin is based on the open-source application Varnish which is a reverse proxy server, it helps to increase the speed of the WordPress Website at times of huge traffic. This cache also becomes a boon when the WordPress site goes down, as the cache will continue to transfer the cached version to the clients.

This Varnish HTTP Purge Plugin can be directly used on the WordPress sites that have Varnish installed in them. This enables the owner to clear the website’s cache manually. Purges also occur automatically in relevant situations such as new contents getting added to the WordPress site. Varnish HTTP is an open-source and free-to-use plugin and does not require any premium tier for installation.

In order to experience a greater performance of the WordPress site, it is recommended to use Varnish Cache along with internal caching plugins like W3 Total Cache or WP Super Cache.

Varnish Cache Vs Redis

Redis is an in-memory database that resides on a disk. Redis is often referred to as an open-source, BSD licensed and an advanced key-value store. It is actually a data structure server which includes keys that contain strings, hashes, lists, sets and sorted sets.

Caches in Redis follow a mechanism called data eviction to make space available for the new data by deleting existing data from the memory. Redis follows six different eviction policies for eliminating the existing data. Redis also supports both lazy and active eviction where old data gets deleted only when more space is required proactively.

Varnish Cache, on the other hand, is a web application accelerator also referred to as caching HTTP reverse proxy. It is installed in front of the server and includes HTTP and configures it to cache the contents. Varnish Cache is very fast and increases the speed of delivery with a factor of 300-1000x depending on the structural design of the website.

The Varnish is heavily threaded and each client connection is handled by a separate worker thread. The incoming connection requests are normally placed in an overflow queue when an active worker thread reaches its configuration limit. If the overflow queue also reaches its configuration limit incoming connections will be rejected.

Redis provides more flexibility regarding the objects that can be cached. Redis permits key names and values to be as huge as 512MB each. Redis helps to develop software that handles thousands of requests per second and retains customer business data throughout the natural life cycle.

Redis is classified as a tool in the In-Memory Databases category while Varnish is classified under Web-cache. Both Redis and Varnish Cache are noted for its performance, speed and ease of use. Even though the stability of Varnish is better than Redis, Redis has a broader approval.

Varnish Cache Server error

If a website makes use of Varnish Cache, there are chances that at some point of time the user might encounter Varnish Cache Server Error: Error 503 or Server Unavailable/Guru Meditation with an XID number. Such an error indicates that the respective website is using VC to cache and serve data and that the Varnish Cache is not able to reach the backend server. VC sends the Guru Meditation error when the connection gets timed out or its server has several requests transferred to the backend server without getting any response. Instead of continually transferring requests to an unhealthy backend server, the Varnish Cache issues the 503 error and lets the user know that the website manager is working on the issue and it is suggested to try again later.

Fixing a Varnish Cache Server

If a website is issuing a Guru Meditation 503 error through Varnish Cache, the first step is to view the log for all 503 errors by using Varnishlog. The command $ varnishlog -q ‘RespStatus == 503’ -g request is used to display the 503 errors in Varnishlog.

Frequent 503 errors might be due to the reason that the backend server is down. It is also required to verify the port the VC is trying to connect the main server and the HTTP service like Apache or Nginx and ensure that all of them are operating properly. If they are working properly, it is required to troubleshoot at the backend.

If the backend server seems to be up and still if 503 error gets displayed, then some issue might exist with the connection between the web server and Varnish Cache or with the VC Configuration. The Varnish Cache error 503, in this case, might also occur due to timeouts. The timeout length in the backend default VCL section can be modified using the command a.connect_timeout = Xs and a. first_byte_timeout = Xs to an appropriate timeout length that works for the webserver. One more option available is to disable KeepAlive so that the idle connections will be dropped.

Varnish Cache API

The goal of caching is to ensure that the same response is not generated twice. The purpose of such a goal is to gain speed and minimize the server load. The best method to cache an API is to place a reverse proxy in front of it. One of the best open-source reverse proxies is the Varnish Cache. The Caching power of Varnish API delivers scalable, high-performance content delivery for most of the HTTP and API protocols. Let it be a static file or a complex dynamic content that requires speed, Varnish API delivers everything.

Varnish cache API acts as both an HTTP server and an HTTP client and provides SSL/TSL support to both server and client ends. The SSL/TSL proxy is securely integrated with Varnish and this enhances the security of the website by encrypting communication eliminating the need for third-party security solutions.

Latency is one of the key problems that get resolved by placing a Varnish Cache API between the internal services and external APIs. As the data remains relatively static, external requests can be bypassed entirely. Thus latency is reduced to a great extent when fetching the external resources.

Varnish ensures that the content is accessible and available 24/7 across a global spread of servers. Varnish cache API high availability feature converts pairs of Varnish servers into highly available caching clusters and makes sure the content is always available to the customers. The website performance is also enhanced by reduced cache misses and backend infrastructure is also protected from overload. This also minimizes the risk of backend traffic surges and page load time spikes.

Under unavoidable circumstances where the incoming requests cannot reach the backend server, the Varnish can be configured to transfer the stale content even if the content is purged or expired from the Cache. This means that requests get processed even if an outage exists and stale responses can be served until the issues get resolved. This minimizes the risk of users losing interest and leaving the website to a great extent.

Varnish API also includes a sophisticated control system called Paywall that provides flexible control tools for the website. This permits the owner to set rules on how the users can access any controlled content.

Finally, rate limiting is addressed in the same way as latency. If a decent cache hit ratio exists in Varnish, then obviously fewer responses are made to the main server. This provides a breathing room for the external service to actually face any eventual rate limits.

Varnish easily takes caching to the next level. With its modern architecture which is mainly designed keeping performance in mind, it actually becomes a boon to high-traffic websites and can speed up the performance 300-1000 times faster. Reliability, Flexibility and Affordability are some of the other key benefits of using Varnish Cache. It easily caches even the heavily customized API’s and is definitely one of the most favoured web accelerators in contrast to Apache and NGINX.

You don’t have to arrange Varnish Cache and/or Nginx separately to increase server speed. Being powered by Nginx and Varnish, ApacheBooster makes up a powerful plugin to improve server performance. Therefore, if you have to deal with slow server or website, kindly consider installing it and get the benefits it offers.

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