YSlow: Use a Content Delivery Network (CDN)
Recommendations
- Lighthouse
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- Metrics
- Audits
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- Allow back/forward cache restoration
- Avoid an excessive DOM size
- Avoid chaining critical requests
- Avoid CSS @import
- Avoid document.write()
- Avoid enormous network payloads
- Avoid large layout shifts
- Avoid long main-thread tasks
- Avoid multiple page redirects
- Avoid non-composited animations
- Avoid serving legacy JavaScript to modern browsers
- Avoid unload event listeners (Deprecated)
- Combine images using CSS sprites
- Defer offscreen images
- Don't lazy load Largest Contentful Paint image
- Efficiently encode images
- Eliminate render-blocking resources
- Enable Keep-Alive
- Enable text compression
- Ensure text remains visible during webfont load
- Keep request counts low and transfer sizes small
- Lazy load third-party resources with facades
- Minify CSS
- Minify JavaScript
- Minimize main-thread work
- Preconnect to required origins
- Preload key requests
- Preload Largest Contentful Paint image
- Properly size images
- Reduce initial server response time
- Reduce JavaScript execution time
- Reduce the impact of third-party code
- Reduce unused CSS
- Reduce unused JavaScript
- Remove duplicate modules in JavaScript bundles
- Replace large JavaScript libraries with smaller alternatives (deprecated)
- Serve images in next-gen formats
- Serve static assets with an efficient cache policy
- Use a <meta name="viewport"> tag with width or initial-scale
- Use a Content Delivery Network (CDN)
- Use explicit width and height on image elements
- Use HTTP/2 for all resources
- Use passive listeners to improve scrolling performance
- Use video formats for animated content
- User Timing marks and measures
- PageSpeed (Legacy)
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- Avoid a character set in the meta tag
- Avoid bad requests
- Avoid CSS @import
- Avoid CSS expressions (deprecated)
- Avoid document.write (deprecated)
- Avoid Flash on mobile webpages (deprecated)
- Avoid landing page redirects
- Avoid Plugins (deprecated)
- Combine external CSS (deprecated)
- Combine external JavaScript (deprecated)
- Combine images using CSS sprites
- Defer loading of JavaScript (deprecated)
- Defer parsing of JavaScript
- Enable compression
- Enable Keep-Alive
- Improve server response time (deprecated)
- Inline small CSS
- Inline small JavaScript
- Leverage browser caching
- Leverage proxy caching (deprecated)
- Make landing page redirects cacheable (deprecated)
- Minify CSS
- Minify HTML (deprecated)
- Minify JavaScript
- Minimize cookie size (deprecated)
- Minimize DNS lookups (deprecated)
- Minimize redirects
- Minimize request size
- Optimize images
- Optimize the order of styles and scripts (deprecated)
- Parallelize downloads across hostnames (deprecated)
- Prefer asynchronous resources
- Put CSS in the document head
- Remove query strings from static resources (deprecated)
- Remove unused CSS (deprecated)
- Serve resources from a consistent URL
- Serve scaled images
- Serve static content from a cookieless domain (deprecated)
- Specify a cache validator
- Specify a character set early
- Specify a Vary: Accept-Encoding header (deprecated)
- Specify a viewport for mobile browsers (deprecated)
- Specify image dimensions
- Use an application cache (deprecated)
- Use efficient CSS selectors (deprecated)
- YSlow (Legacy)
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- Add Expires headers
- Avoid AlphaImageLoader filter
- Avoid CSS expressions
- Avoid empty src or href
- Avoid HTTP 404 (Not Found) error
- Avoid URL redirects
- Compress components
- Configure entity tags (ETags)
- Do not scale images in HTML
- Make AJAX cacheable
- Make favicon small and cacheable
- Make fewer HTTP requests
- Make JavaScript and CSS external
- Minify JavaScript and CSS
- Put CSS at the top
- Put JavaScript at bottom
- Reduce cookie size
- Reduce DNS lookups
- Reduce the number of DOM elements
- Remove duplicate JavaScript and CSS
- Use a Content Delivery Network (CDN)
- Use cookie-free domains
- Use GET for AJAX requests
Overview
CDNs can give an equally fast web experience to your users across the globe.
How does your site score on this recommendation?
Details from Yahoo!
The user's proximity to your web server has an impact on response times. Deploying your content across multiple, geographically dispersed servers will make your pages load faster from the user's perspective.
Read our Lighthouse documentation to learn more about using a CDN.
Summary
ServerMedium
Moderate
44%
YSlow recommends:
A content delivery network (CDN) is a collection of web servers distributed across multiple locations to deliver content more efficiently to users.
The server selected for delivering content to a specific user is typically based on a measure of network proximity.
For example, the server with the fewest network hops or the server with the quickest response time is chosen.
Some large Internet companies own their own CDN, but it's cost-effective to use a CDN service provider, such as Akamai Technologies, Mirror Image Internet, or Limelight Networks.
For start-up companies and private web sites, the cost of a CDN service can be prohibitive, but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times.