How CDNs Affect Crawling and SEO?

Content Delivery Networks (CDNs) have become a cornerstone of modern website performance, offering faster load times and better user experiences. However, CDNs also play a critical role in how websites are crawled and indexed by search engines, impacting their SEO performance. This article explores the influence of CDNs on crawling and SEO, highlighting the benefits, challenges, and best practices to optimise their use.

What Is a CDN?

A Content Delivery Network (CDN) is a service that stores cached versions of web pages and serves them from data centres located closer to the user. By reducing the distance data needs to travel, CDNs significantly speed up website loading times. The caching process involves copying web page content and storing it in servers distributed globally.

For example, when a user visits a website, the CDN identifies the nearest server and delivers the cached version of the page from there. This process reduces latency and improves the user experience. Additionally, CDNs lighten the load on the origin server, ensuring better performance even during high-traffic periods.

Benefits of CDNs for Crawling and SEO

CDNs provide several advantages that directly and indirectly affect crawling and SEO. Let’s explore these benefits:

Increased Crawl Rate

When Googlebot detects that a website is served through a CDN, it often increases the crawl rate. This is because CDNs alleviate server strain, allowing more pages to be crawled without slowing down the website. Normally, if Googlebot senses that a server is overloaded, it reduces the crawl rate to avoid further strain. CDNs mitigate this by distributing the load across multiple servers.

Improved Page Load Speed

Page load speed is a critical ranking factor for search engines. CDNs ensure faster delivery of web pages by serving them from the nearest data centre, reducing loading times. Faster pages lead to better user experiences, which in turn improves SEO rankings.

Improved Availability and Reliability

CDNs improve website uptime by distributing traffic across multiple servers. If one server goes down, another takes over, ensuring uninterrupted access. This reliability ensures that Googlebot and other search engine crawlers can consistently access your website.

Efficient Handling of Large Websites

For websites with millions of pages, CDNs are invaluable. They help manage the “crawl budget”—the number of pages Googlebot is allowed to crawl in a given timeframe. By reducing server load, CDNs enable more efficient crawling, ensuring that search engines index a larger portion of the website.

Challenges of Using CDNs for Crawling and SEO

While CDNs offer numerous benefits, they can also introduce issues that hinder crawling and negatively affect SEO. Understanding these challenges is essential to optimise your CDN setup.

Initial Cache Warm-Up

The first time a URL is accessed, the CDN’s cache is “cold,” meaning the content hasn’t been cached yet. During this period, the origin server must serve the request directly. For websites with many pages, this can put a significant strain on the server and consume a large portion of the crawl budget. Google advises being cautious when launching numerous URLs at once, as the initial crawl rate may be high until the cache is fully populated.

Hard Blocks

Hard blocks occur when a CDN unintentionally prevents crawlers from accessing web pages. This can happen due to server errors or misconfigured settings. Common hard block scenarios include:

• 500 Internal Server Error: Indicates a significant server issue, causing Googlebot to slow down crawling.
• 502 Bad Gateway: Signals communication problems between servers, leading to crawling delays.
• Random Errors: Occur when error pages are incorrectly served with a 200 status code (indicating success). Google may interpret these as duplicate pages and remove them from the index.

Soft Blocks

Soft blocks happen when a CDN presents bot-verification interstitials, such as CAPTCHAs, to crawlers. If these interstitials do not send the correct HTTP status code (503 Service Unavailable), Googlebot may interpret the content as permanently unavailable, leading to deindexation.

IP Blocking

CDN firewalls, known as Web Application Firewalls (WAFs), may mistakenly block Googlebot’s IP addresses. This can happen if Google’s IPs are flagged as malicious by automated systems. Such blocks prevent crawlers from accessing the site, impacting indexing and visibility.

Best Practices for Optimising CDNs for SEO

To maximise the benefits of CDNs while avoiding common pitfalls, follow these best practices:

Configure HTTP Status Codes Correctly

Ensure that your server responds with appropriate HTTP status codes for different scenarios:

• Use 503 Service Unavailable for temporary issues, such as bot-verification interstitials or maintenance. This signals to Googlebot that the issue is temporary.
• Avoid serving error pages with a 200 OK status, as this confuses crawlers and may lead to deindexation.
• Address repeated 500 Internal Server Errors and 502 Bad Gateway responses promptly to prevent crawling slowdowns.

Monitor Cache Performance

Regularly check the status of your CDN’s cache. Ensure that frequently accessed pages are always cached to reduce strain on the origin server. Use analytics tools provided by your CDN to identify and address cache-miss issues.

Inspect URL Access

Use Google’s URL Inspection Tool in Search Console to see how your pages are being crawled. This tool provides insights into whether Googlebot can access your web pages correctly.

Review Firewall Configurations

Ensure that your Web Application Firewall (WAF) allows Googlebot and other important crawlers to access your website. Compare blocked IP addresses against Google’s official IP list to identify and unblock legitimate crawlers.

Optimise Crawl Budget

Be mindful of your crawl budget, especially when launching a large number of pages. Spread out new URL launches over time to avoid overwhelming the origin server during the cache warm-up phase.

Regularly Audit CDN Settings

Periodically review your CDN configurations to ensure optimal performance. Look for settings that might inadvertently block crawlers or cause unnecessary errors.

Debugging CDN Issues

When issues arise, debugging is essential to restore proper functionality. Here’s how to troubleshoot common CDN-related problems:

• Check Server Logs: Analyse server logs to identify patterns in blocked requests or error responses.
• Use Search Console: The URL Inspection Tool provides detailed information about how Googlebot views your pages.
• Test Response Codes: Use online tools or browser developer tools to verify the HTTP status codes returned for different pages.
• Consult CDN Support: Reach out to your CDN provider for assistance with advanced troubleshooting.

Conclusion

Content Delivery Networks (CDNs) are powerful tools for enhancing website performance and improving SEO. By increasing crawl rates, speeding up page load times, and ensuring high availability, CDNs provide a strong foundation for search engine optimisation. However, improper configuration or maintenance can lead to crawling issues that negatively impact SEO performance.

To harness the full potential of CDNs, follow best practices such as configuring correct HTTP status codes, monitoring cache performance, and reviewing firewall settings. Regular audits and proactive debugging can help prevent common problems, ensuring that your website remains accessible to both users and search engine crawlers.

By understanding the interplay between CDNs, crawling, and SEO, website owners and SEOs can create a robust online presence that ranks well and delivers a seamless user experience.