Scaling WordPress For High Traffic: Caching, Cdns And Load Balancing

Caching Strategies to Improve Page Load Speed

Leveraging caching strategies is crucial for optimizing WordPress sites to handle high traffic loads. By caching elements of a WordPress site, we can significantly reduce server load and improve page load speeds by serving cached content instead of dynamically generating pages on every request. There are several effective caching techniques that can be implemented:

Leveraging Browser Caching

Browser caching allows browsers to store static assets and files locally so they don’t need to be re-downloaded on every page request. This can include images, CSS files, JavaScript files, fonts, and other media. To leverage browser caching in WordPress:

• Install a caching plugin like WP Rocket or W3 Total Cache and enable the browser cache functionality
• Set far future Expires headers for static resources through `.htaccess` rules
• Specify a Cache-Control header specifying max-age directive
• Use content delivery networks (CDNs) to distribute static assets and leverage their caching (covered more in next section)

Implementing a PHP Cache

A PHP cache stores pre-compiled bytecode cache of PHP scripts to avoid needing to re-compile on every page load. This can significantly speed up processing time. To implement a PHP cache:

• Install a dedicated PHP caching plugin like PHP OPcache, which is included in PHP 7+
• Enable the cache and configure optimal directives for memory allocation and consistency checks
• Consider a proxy cache like Varnish to cache full pages in memory

Enabling a Page Cache Plugin

A page caching plugin for WordPress lets you cache full HTML pages, avoiding CPU-intensive database queries and PHP processing on each request. This can dramatically improve performance for high traffic loads. To enable page caching:

• Install a dedicated page caching plugin like WP Rocket, WP Fastest Cache or LiteSpeed Cache
• Configure cache times and triggers – aim for a balance of speed and keeping content fresh
• Set up purge rules for when certain actions should clear the cache automatically

Content Delivery Networks (CDNs) for Faster Asset Loading

A content delivery network (CDN) distributes static files and assets across a global network of edge servers, caching them in memory near visitors for faster loading speeds. Integrating a CDN effectively offloads asset delivery from the origin server. Key steps when leveraging a CDN include:

Choosing a Reliable CDN Provider

• Research leading CDN providers like Cloudflare, KeyCDN, StackPath and BunnyCDN
• Evaluate pricing models (some offer free tiers) and bandwidth needs
• Review performance benchmarks for global coverage and caching efficiency
• Assess ease of use and configuration with WordPress

Configuring a CDN in wp-config.php

To directly integrate a CDN with WordPress using wp-config.php:

• Sign up for an account with your chosen CDN provider
• Map your domain name to the CDN and configure an origin pull for your server
• Get the CDN URL endpoints for assets
• Add the constants WP_CONTENT_URL and WP_PLUGIN_URL in wp-config.php pointing at CDN URLs

Pointing to CDN URLs in Functions.php

Alternatively, you can use functions.php to have WordPress dynamically replace local URLs with CDN counterparts:

• Sign up and configure your domain with the CDN as above
• In functions.php, hook into template_redirect
• Use the Output Buffer to replace file paths with CDN URLs
• Take care to preserve URL schema and relative paths

Scaling Web Servers with Load Balancing

When optimizing WordPress for peak traffic, a single web server may not be able to handle the request load. Load balancing allows you to distribute traffic across multiple servers to spread the load and create redundancy. Key components include:

Setting up a Load Balancer

• A load balancer sits in front of your web servers, distributing requests across them
• Can be hardware-based or increasingly software-based like HAProxy
• Looks for servers that are online and have available capacity to handle requests
• Leading cloud providers like AWS offer managed load balancers

Configuring Multiple Web Servers

Behind the load balancer, you need to set up mirrored WordPress servers to handle traffic:

• Add server capacity by provisioning more compute instances to handle increased loads
• Install WordPress on each instance with identical configurations for plugins, themes and files
• Link all servers to the same database backend to sync data
• Optional master-slave database topology further improves scalability

Implementing Health Checks

For maximum uptime, load balancers use health checks to monitor web server status:

• Load balancers periodically ping endpoints on each server to check responsiveness
• If a server exceeds thresholds for failures, it is temporarily removed from the pool
• Ensures traffic is only routed to available servers, preventing downstream issues

Additional Tips for Handling Spikes in Traffic

In addition to adding server capacity and implementing caching and CDNs, there are some other WordPress performance optimizations worth considering when planning for traffic spikes:

Optimizing Images and Media

• Use image optimization plugins like EWWW Image Optimizer to compress images
• Downsize overly large images to appropriate resolutions
• Lazy load below-the-fold images to delay offscreen loading
• Serve images from a cloud storage service like Amazon S3 for offloading

Enabling GZIP Compression

• GZIP compressing of HTML, JavaScript, CSS and textual assets
• Drastically reduces filesize sent over-the-wire improving transfer speeds
• Enable compression in PHP and server configs or via caching plugins

Installing a Plugin to Defer Offscreen Images

• Defer loading of offscreen images with plugin to accelerate initial page load
• Display images only as user scrolls down to view them
• Improves perceived performance – pages start rendering faster above-the-fold