Varnish
Varnish is an open source web application accelerator designed to speed up websites by caching and optimizing content delivery. It sits in front of web servers and caches frequently-accessed content, reducing requests to backend servers.
caching
content-delivery
acceleration
Varnish: Open Source Web Application Accelerator
Caching and optimizing content delivery to speed up websites, Varnish sits in front of web servers and reduces requests to backend servers.
What is Varnish?
Varnish is an open source web application accelerator designed to speed up websites by caching and optimizing content delivery. It works by sitting in front of web servers like Apache or Nginx and caching frequently-accessed content in memory, reducing requests that need to be sent to slower backend servers and databases.
When a user requests a page from a site running Varnish, it first checks if it has a cached version. If so, it quickly serves the cached content without needing to query the application servers. If not, it passes the request to the application servers to generate the page, stores it in the cache, and then serves it to the user.
Key features of Varnish include:
- Caching of HTML pages, images, and API responses in memory for faster delivery
- Support for load balancing across backend application servers
- Advanced HTTP handling with features like compression, streaming, and SSL termination
- Powerful configuration language to set caching policies and control what gets cached
- Monitoring tools for testing cache hit ratio and inspecting what is in the cache
Because Varnish caches entire pages and assets in memory, it is significantly faster than application-level caches that have to query the database. Site owners typically see substantial improvements in website performance after implementing Varnish, with reports of 3x-10x speed improvements. It handles heavy traffic effectively and can dramatically reduce server load in high-traffic scenarios.
Varnish is used by many high-profile websites including Facebook, Wikipedia, Vimeo, and Twitter. It runs on most Linux distributions and is used together with popular web servers like Nginx, Apache, and Lighttpd. Varnish provides an excellent way for site owners to accelerate web applications without modifying application code.
Varnish Features
Features
- Caching and optimization of content delivery
- Speeds up websites by reducing requests to backend servers
- Sits in front of web servers as a reverse proxy
- Supports load balancing
- Caching of static and dynamic content
- Caching rules based on URLs, cookies, device type, etc
- Health checks for origin servers
- Grace mode to serve stale content if backends are down
- Edge Side Includes for dynamic caching
- Logging and monitoring capabilities
Pricing
- Open Source
Pros
Significant performance improvements
Reduces load on backend servers
Open source with active development community
Highly configurable and customizable
Integrates well with many frameworks/CMSs
Can scale horizontally with multiple Varnish servers
Cons
Complex configuration
Steep learning curve
No GUI, managed via command line
Caching needs to be configured properly
Not ideal for sites with highly dynamic content
Official Links
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