Cloudflare bypass cache for subdomain

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To solve the problem of Cloudflare bypassing cache for a subdomain, here are the detailed steps:

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  1. Understand Cloudflare’s Caching Logic: Cloudflare caches content based on various factors, including cache-control headers, file extensions, and page rules. By default, it caches static content images, CSS, JS and often respects origin server headers. For subdomains, the caching behavior can sometimes differ from the main domain, or settings might be inherited in unexpected ways.

  2. Identify the Subdomain’s DNS Records:

    • Log in to your Cloudflare dashboard.
    • Navigate to the specific domain.
    • Go to the DNS tab.
    • Locate the A or CNAME record for your subdomain e.g., blog.yourdomain.com.
    • Ensure its proxy status the orange cloud icon is Proxied. If it’s DNS Only grey cloud, Cloudflare won’t process traffic for it, and thus won’t cache it. Click the cloud to toggle it to orange if it’s grey.

  3. Check Cloudflare’s Caching Level Settings:

    • In the Cloudflare dashboard, go to Caching > Configuration.
    • Review the “Caching Level” setting.
    • Standard: Caches static files CSS, JS, images, fonts.
    • Aggressive: Caches static files and might cache more content, even if not explicitly specified by origin headers.
    • Basic: Caches fewer file types.
    • For consistent caching, “Standard” is usually sufficient, but “Aggressive” can be explored if you need more robust caching for static assets.

  4. Implement Page Rules for Specific Subdomain Caching: This is often the most precise way to control caching for subdomains.

    • Go to Rules > Page Rules.
    • Click “Create Page Rule.”
    • For the URL pattern, be very specific: Use *subdomain.yourdomain.com/* e.g., *blog.yourdomain.com/*. The asterisks are crucial for matching all paths and protocols.
    • Add settings:
      • Caching Level: Select “Cache Everything” if you want Cloudflare to cache all content for the subdomain, including HTML. Be cautious with dynamic content. ensure your origin server handles Cache-Control headers appropriately to prevent stale content.
      • Edge Cache TTL: Set this to your desired duration e.g., “1 hour,” “1 day,” “a month”. This dictates how long Cloudflare will store the cached content before re-fetching from your origin.
      • Browser Cache TTL: Set this to “Respect Existing Headers” usually, or a specific time if you want to override your origin’s browser cache settings.
      • Disable Performance: Optional If you notice any unexpected behavior, you might temporarily disable other performance features within this rule.
    • Order of Rules: Cloudflare processes page rules from top to bottom. More specific rules should be placed higher. Ensure this subdomain rule is above any broader domain rules that might conflict.

  5. Configure Origin Server Headers Crucial: Cloudflare largely respects Cache-Control and Expires headers from your origin server.

    • Ensure your web server Nginx, Apache, IIS is sending appropriate Cache-Control headers for the subdomain’s content.
      • Cache-Control: public, max-age=3600 caches for 1 hour for public caches like Cloudflare
      • Cache-Control: no-cache tells caches to revalidate with the origin before serving
      • Cache-Control: no-store prevents any caching
    • If content isn’t caching, check if your server is sending Cache-Control: no-cache or no-store or very low max-age values. Adjust these to higher values for cacheable content.

  6. Purge Cache: After making any changes, it’s essential to purge the cache.

    • In Cloudflare, go to Caching > Configuration.
    • Click “Purge Everything” if you want to clear all cached content for the domain or “Custom Purge” to purge specific URLs or hostnames e.g., blog.yourdomain.com/*.

  7. Test and Monitor:

    • Use browser developer tools Network tab to check the cf-cache-status header.
      • HIT: Content served from Cloudflare cache.
      • MISS: Content fetched from origin.
      • DYNAMIC: Content not cached, typically because it’s dynamic or a rule prevented caching.
      • BYPASS: Content explicitly bypassed caching e.g., via a Page Rule or header.
    • Use curl -svo /dev/null https://blog.yourdomain.com/your-page.html to see the full response headers and verify cf-cache-status.

Remember, the goal is to have cf-cache-status: HIT for the content you intend to cache.

If you’re consistently getting MISS or BYPASS, re-evaluate your Page Rules and origin server headers.

Optimizing Cloudflare Caching for Subdomains: A Deep Dive

Leveraging Cloudflare for your web properties, including subdomains, is a shrewd move for enhancing performance and security.

However, mastering its caching mechanisms for subdomains requires a nuanced approach.

While the main domain might hum along with optimal caching, subdomains sometimes present unique challenges, potentially leading to content being served directly from the origin server rather than Cloudflare’s global network of 300+ cities.

This can impact loading times, consume more origin server resources, and diminish the very benefits Cloudflare is meant to provide.

The Anatomy of Cloudflare’s Caching Engine

Cloudflare’s caching engine operates on a sophisticated logic, deciding whether to serve content from its edge network or proxy the request to your origin server. It considers numerous factors, from HTTP headers sent by your server to specific rules configured within the Cloudflare dashboard. Understanding these foundational principles is paramount to effectively bypassing cache for a subdomain when necessary, or conversely, ensuring it is cached when desired. Approximately 90% of Cloudflare’s total traffic is served from cache, highlighting the significant impact of proper caching configuration.

Cloudflare’s Global Network Advantage

Cloudflare’s network comprises data centers strategically located worldwide.

When a user requests content, Cloudflare routes them to the nearest data center.

If the content is cached there, it’s served instantly, reducing latency. This proximity is critical.

For instance, a user in London accessing a server in New York might experience 100-150ms of latency, but if served from Cloudflare’s London data center, this drops to single-digit milliseconds.

The Role of HTTP Headers in Caching

HTTP headers are the silent communicators between your server, Cloudflare, and the user’s browser. Best proxy to bypass cloudflare

Key headers like Cache-Control, Expires, and ETag dictate caching behavior.

  • Cache-Control: This is the most important header for modern caching. Directives like public, private, no-cache, no-store, max-age, and s-maxage instruct caches on how to handle the response. For Cloudflare, public and a high max-age or s-maxage are critical for optimal caching. For example, Cache-Control: public, max-age=86400 tells Cloudflare and browsers to cache content for 24 hours.
  • Expires: An older header, but still respected. It specifies an absolute date/time after which the response is considered stale.
  • Pragma: Primarily for backward compatibility with HTTP/1.0 caches, often used with no-cache.

Understanding and configuring these on your origin server is foundational.

Many applications and web servers Apache, Nginx, IIS have default caching behaviors, which you might need to override or specifically configure for subdomains.

Common Reasons for Subdomain Cache Bypasses

When a subdomain isn’t caching as expected, it’s not usually a mysterious glitch but rather a logical outcome of specific configurations or omissions.

Diagnosing these reasons systematically is key to resolving the issue.

Data from Cloudflare indicates that a significant percentage of “cache misses” are due to misconfigured headers or incorrect Cloudflare settings rather than inherent system limitations.

Origin Server Cache-Control Headers

This is arguably the most frequent culprit.

If your origin server for the subdomain is sending Cache-Control: no-cache, no-store, or a very low max-age e.g., max-age=0, Cloudflare will respect this directive and not cache the content, or revalidate it on every request.

This often happens with dynamic content or pages that are frequently updated, but it can sometimes be inadvertently applied to static assets.

  • Example: A WordPress installation on a subdomain might send no-cache for all HTML pages by default, preventing Cloudflare from caching them unless a specific Page Rule overrides this.

Cloudflare DNS Proxy Status Orange Cloud

For Cloudflare to process and cache traffic for a subdomain, its DNS record within Cloudflare must be set to “Proxied” the orange cloud icon. If it’s “DNS Only” grey cloud, traffic bypasses Cloudflare entirely, going directly to your origin server. This means no caching, no WAF, and no CDN benefits from Cloudflare for that specific subdomain. This is a common oversight, especially when setting up new subdomains. Bypass cloudflare javascript

Conflicting Cloudflare Page Rules

Cloudflare’s Page Rules are powerful, but their order and specificity matter immensely. If you have a broader Page Rule that applies to yourdomain.com/* and sets caching to “Bypass,” it might inadvertently affect subdomain.yourdomain.com if a more specific rule for the subdomain isn’t placed higher or configured correctly. Rules are processed in the order they appear in the dashboard, and the first matching rule takes precedence.

Query Strings and Dynamic Content

By default, Cloudflare’s “Standard” caching level treats URLs with query strings ?param=value as unique resources and often bypasses caching for them, assuming they represent dynamic content.

If your subdomain uses query strings for tracking or content variation e.g., blog.yourdomain.com/post?id=123, this can lead to cache misses.

You can configure Cloudflare to ignore query strings for caching purposes using Page Rules, but this requires careful consideration to avoid serving stale content.

Cloudflare Cache-Level Settings

The overall “Caching Level” setting under the Caching section of your Cloudflare dashboard Standard, Aggressive, Basic influences default caching behavior.

While “Standard” is often sufficient, if you’re expecting more aggressive caching for static assets, ensure it’s not set to “Basic” or that a Page Rule isn’t overriding it.

Specific File Types Not Cached

Cloudflare’s default caching only applies to certain static file extensions e.g., .css, .js, .jpg, .png, .gif, .pdf, .mp3, .mp4. If your subdomain serves other file types that you expect to be cached e.g., .json API responses, you’ll need a “Cache Everything” Page Rule or explicit Cache-Control headers.

Configuring Page Rules for Subdomain Caching Control

Page Rules are the Swiss Army knife for fine-tuning Cloudflare’s behavior. They allow you to define specific actions based on URL patterns, offering granular control over caching, security, and performance features for your subdomains. Cloudflare provides up to 3 Page Rules for free accounts, with more available on paid plans, making their efficient use crucial.

Step-by-Step Page Rule Creation

  1. Access Page Rules: Log in to your Cloudflare dashboard, select the domain, and navigate to Rules > Page Rules.
  2. Create New Rule: Click “Create Page Rule.”
  3. Define URL Pattern: This is the most critical part. To target a subdomain and all its paths, use the pattern: *subdomain.yourdomain.com/*.
    • The first asterisk * matches any protocol http/https and any subdomain prefix though usually you’d be specific like blog.yourdomain.com.
    • subdomain.yourdomain.com is your actual subdomain.
    • The trailing asterisk /* matches any path or query string on that subdomain.
    • Example for a blog subdomain: *blog.yourdomain.com/*
  4. Add Settings Actions: Choose the actions you want Cloudflare to take when a request matches the URL pattern.
    • Caching Level: “Cache Everything”
      • This powerful setting instructs Cloudflare to cache every response for the matched URL, including HTML, regardless of origin Cache-Control headers though it still respects no-store. Use with caution for dynamic content.
      • Use Cases: Static websites, blog posts, product pages that don’t change often.
      • Caveats: If your content is highly dynamic e.g., user-specific dashboards, e-commerce checkouts, “Cache Everything” can lead to serving stale or incorrect data. For such scenarios, consider “Bypass” or relying solely on origin headers.
    • Edge Cache TTL: This determines how long Cloudflare’s edge servers will store content before re-fetching from your origin.
      • Options: From “a minute” to “a month,” or “Respect Existing Headers.”
      • Recommendation: Set this to a duration that balances freshness with performance. For static assets or rarely updated pages, “a month” is ideal. For frequently updated content, “1 hour” or “4 hours” might be more appropriate.
    • Browser Cache TTL: This controls how long users’ browsers will cache content. Often, “Respect Existing Headers” is sufficient, allowing your origin server to dictate browser caching.
    • Disable Performance: If you want to explicitly prevent caching for a subdomain i.e., ensure it always bypasses Cloudflare’s cache, you can use a Page Rule with “Caching Level: Bypass” or “Disable Performance” combined with other settings. This is useful for backend APIs or highly personalized content.
  5. Order Matters: Arrange your Page Rules in the correct order. Cloudflare processes rules from top to bottom. More specific rules should be placed above broader rules that might otherwise override them.

Best Practices for Page Rules

  • Be Specific: Use the most precise URL patterns possible to avoid unintended consequences.
  • Combine Actions: Group related actions within a single rule e.g., Cache Everything and Edge Cache TTL.
  • Test Thoroughly: After implementing a new rule, clear your Cloudflare cache and test the subdomain using browser developer tools and curl to verify the cf-cache-status header.
  • Monitor Rule Usage: Keep an eye on your Page Rule usage to ensure you’re not exceeding limits if on a free plan.

Fine-Tuning Origin Server Cache-Control Headers

While Cloudflare Page Rules offer powerful overrides, the best practice is to have your origin server send appropriate Cache-Control headers.

This gives you granular control at the application level and ensures consistent caching behavior across all layers Cloudflare, other CDNs, user browsers. Many developers overlook this critical step, assuming Cloudflare will handle everything. Free cloudflare bypass

Understanding Cache-Control Directives

  • public: Indicates that the response can be cached by any cache, including shared public caches like Cloudflare.
  • private: Indicates that the response is intended for a single user and cannot be cached by shared caches. Used for user-specific data.
  • no-cache: Tells caches to revalidate with the origin server before serving a cached copy. It does not mean “do not cache.”
  • no-store: The strongest directive. prevents any caching by any cache. Use for highly sensitive or truly dynamic content.
  • max-age=<seconds>: Specifies the maximum amount of time a resource is considered fresh. Cloudflare will respect this.
  • s-maxage=<seconds>: Similar to max-age but applies only to shared caches like Cloudflare. This allows you to set a longer cache time for Cloudflare while maintaining a shorter max-age for client browsers.
  • must-revalidate: Forces caches to revalidate stale entries with the origin.

Configuring Headers in Popular Web Servers

  • Nginx: Use the expires directive within your location or server blocks.

    location ~* \.jpg|jpeg|gif|png|css|js|ico|woff|woff2|ttf|eot$ {
   expires 30d. # Cache for 30 days


   add_header Cache-Control "public, max-age=2592000".
}

location / {
   # For HTML or dynamic content, ensure appropriate headers
   add_header Cache-Control "public, max-age=3600". # Cache HTML for 1 hour

    For specific subdomains, you can have a separate server block:
    server {
    listen 80.
    server_name blog.yourdomain.com.

    location / {

    add_header Cache-Control “public, max-age=3600”.
    }

    location ~* .jpg|jpeg|gif|png|css|js$ {
    expires 30d.

    add_header Cache-Control “public, max-age=2592000”.

  • Apache: Use mod_headers and mod_expires. Ensure these modules are enabled.

    <IfModule mod_headers.c>
   <FilesMatch "\.html|htm|js|css|gif|png|jpg|jpeg|svg|ico$">


       Header set Cache-Control "public, max-age=3600"
    </FilesMatch>
</IfModule>

<IfModule mod_expires.c>
    ExpiresActive On
    ExpiresDefault "access plus 1 hour"


   ExpiresByType image/jpeg "access plus 1 month"


   ExpiresByType text/css "access plus 1 week"


You can place these directives in your virtual host configuration for the subdomain.

  • IIS: Configure clientCache in web.config or through the IIS Manager.

    <configuration>
  <system.webServer>
    <staticContent>


     <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="30.00:00:00" />
    </staticContent>
    <httpProtocol>
      <customHeaders>


       <add name="Cache-Control" value="public, max-age=3600" />
      </customHeaders>
    </httpProtocol>
  </system.webServer>
</configuration>


For specific paths or file types, you might need more granular rules.

Impact on Cache-Control Headers

By sending appropriate Cache-Control headers from your origin, you provide Cloudflare with clear instructions. If your origin sends max-age=0 or no-cache for content you want cached, Cloudflare will largely respect that, resulting in a cache bypass. Overriding this with a “Cache Everything” Page Rule is possible, but it’s generally better to align your origin’s headers with your caching strategy.

Leveraging the Cloudflare Cache API for Advanced Control

For highly dynamic applications or those requiring precise control over caching behavior programmatically, Cloudflare offers a powerful Cache API. Cloudflare bypass cache header

This API allows developers to interact directly with Cloudflare’s cache, going beyond simple Page Rules to purge specific URLs, pre-fetch content, or even store custom responses at the edge.

What is the Cloudflare Cache API?

The Cache API is part of Cloudflare Workers, a serverless platform that runs JavaScript at Cloudflare’s edge locations.

Workers intercept HTTP requests and responses, allowing you to modify them or serve content directly from the edge cache.

This means you can write custom logic to decide what gets cached, for how long, and under what conditions, offering unparalleled flexibility.

While traditional Page Rules are pattern-based, the Cache API enables logic-based caching decisions.

Use Cases for Subdomains

  • Selective Caching of Dynamic Content: Imagine a subdomain hosting an API that serves public data, but some endpoints are highly dynamic while others are relatively static. With the Cache API, you can write a Worker script to cache only the static API responses based on specific request parameters, headers, or even the response body content. This bypasses caching for truly dynamic requests while optimizing for the rest.
  • Conditional Purging: Instead of purging the entire subdomain, you can programmatically purge specific URLs or content based on events e.g., a database update, a new blog post publication. This ensures freshness without invalidating unrelated cached assets.
  • Pre-fetching and Warming Cache: For critical subdomain content e.g., a new landing page, you can write a Worker to actively pre-fetch and store it in Cloudflare’s cache before users even request it, ensuring instant hits.
  • A/B Testing with Cache Control: Implement A/B testing logic directly at the edge, where different versions of content are served and cached based on user segments or cookies, bypassing cache for specific test groups if needed.
  • Personalized Content Handling: For subdomains serving personalized content, you can use Workers to bypass caching for authenticated users while caching the generic version for unauthenticated visitors.

Example: Conditional Cache Bypass with a Worker

Consider a subdomain api.yourdomain.com where you want to cache all responses unless a specific X-No-Cache header is present in the request.

addEventListener'fetch', event => {
  event.respondWithhandleRequestevent.request
}

async function handleRequestrequest {
  const url = new URLrequest.url



 // Check if a specific header exists to bypass cache


 if request.headers.get'X-No-Cache' === 'true' {


   // If header is present, fetch from origin directly and bypass cache
    const response = await fetchrequest.


   return new Responseresponse.body, response. // Return origin response
  }



 // Otherwise, try to serve from cache or fetch and cache


 const cacheKey = new Requesturl.toString, request.
  const cache = caches.default.

  let response = await cache.matchcacheKey.

  if !response {
    // If not in cache, fetch from origin
    response = await fetchrequest.



   // Make sure the response is cacheable e.g., status 200


   // And add a Cache-Control header if origin doesn't provide it
    if response.status === 200 {


     const newResponse = new Responseresponse.body, response.


     // You can override/add Cache-Control headers here if needed


     // newResponse.headers.set'Cache-Control', 'public, max-age=3600'.


     event.waitUntilcache.putcacheKey, newResponse.clone. // Cache the response
      return newResponse.

  return response.
}

This is a basic example, but it illustrates how you can build sophisticated caching logic tailored to your subdomain’s needs.

The Cache API is an advanced feature, but for complex caching requirements, it offers unmatched power.

Testing and Validating Subdomain Caching Behavior

After implementing any caching configuration changes, whether through Page Rules, origin server headers, or Workers, rigorous testing is non-negotiable.

Blindly trusting settings can lead to stale content, performance regressions, or increased origin load. Cloudflare bypass link

Real-world testing is key to confirming that Cloudflare is behaving as expected for your subdomain.

Utilizing Browser Developer Tools

The network tab in your browser’s developer tools F12 or Cmd+Option+I is your first line of defense.

  1. Open Developer Tools: Navigate to the subdomain in question.
  2. Go to Network Tab: Refresh the page or perform the action that triggers the content load.
  3. Inspect Resources: Click on a specific resource HTML, CSS, JS, image.
  4. Check Headers: Look for the “Response Headers” section.
    • cf-cache-status: This is the most important Cloudflare-specific header.
      • HIT: Indicates the content was served from Cloudflare’s cache. This is what you want for cached assets.
      • MISS: Content was fetched from your origin server. This happens on the first request for content or after a cache purge. Subsequent requests for the same resource should ideally be HIT.
      • DYNAMIC: Cloudflare determined the content was dynamic and did not cache it by default. Often seen for HTML or pages with query strings without specific Page Rules.
      • BYPASS: Content explicitly instructed to bypass cache e.g., via a Page Rule or an X-Cache-Control: no-cache header.
      • EXPIRED: The cached content at the edge expired, and Cloudflare revalidated with the origin.
    • Cache-Control: Verify that your origin server is sending the correct Cache-Control headers for the resource.

Using curl for Command-Line Inspection

curl is an invaluable tool for inspecting HTTP headers directly, bypassing browser caching and extensions.

curl -svo /dev/null https://subdomain.yourdomain.com/path/to/resource.html 2>&1 | grep -iE "cf-cache-status|cache-control|expires"
*   `-s`: Silent mode no progress meter.
*   `-v`: Verbose mode shows request and response headers.
*   `-o /dev/null`: Discards the response body.
*   `2>&1`: Redirects stderr where verbose output goes to stdout.
*   `grep -iE "..."`: Filters output to show only relevant headers.

Example Output showing cache HIT:
< CF-Cache-Status: HIT
< Cache-Control: public, max-age=3600
< Expires: Thu, 01 Jan 2024 12:00:00 GMT
Example Output showing cache MISS:
< CF-Cache-Status: MISS
< Cache-Control: public, max-age=0


This command helps you quickly see if the content is being cached by Cloudflare and what cache headers your origin server is sending.

Run it multiple times to confirm `HIT` status after an initial `MISS`.

 Utilizing Cloudflare Analytics


Cloudflare's dashboard provides detailed analytics on caching.
1.  Go to Analytics: In your Cloudflare dashboard, navigate to Analytics > Traffic.
2.  Filter by Hostname: You can filter traffic by hostname to specifically view data for your subdomain.
3.  Cache Ratio: Look at the "Cache Ratio" metric. A higher ratio indicates more content is being served from cache. You can see this over time to identify trends.
4.  Bypassed vs. Cached Requests: The analytics also show how many requests were served from cache versus those that bypassed it, giving you a high-level overview of your caching efficiency for the subdomain.

# Potential Pitfalls and Troubleshooting Tips

Even with careful configuration, caching can be tricky. Understanding common pitfalls and having a systematic troubleshooting approach will save you time and frustration. A study by CDN provider Akamai found that over 60% of website performance issues are related to improper caching configurations.

 Caching Dynamic Content and when NOT to
*   Pitfall: Attempting to "Cache Everything" for highly personalized or dynamic content e.g., shopping cart, user dashboard, sensitive API responses.
*   Result: Users see stale, incorrect, or even another user's data. This is a critical security and user experience issue.
*   Solution: For truly dynamic content, use Page Rules to set "Caching Level: Bypass" or rely on your origin server sending `Cache-Control: no-store` or `private`. For semi-dynamic content, consider Cloudflare Workers to implement more granular caching logic.

 HTTPS Mixed Content Issues
*   Pitfall: If your subdomain is served over HTTPS, but some assets are linked using HTTP e.g., `http://subdomain.yourdomain.com/image.jpg`, browsers will block them as "mixed content," and Cloudflare might not cache them optimally.
*   Result: Broken images, missing CSS/JS, or security warnings.
*   Solution: Ensure all assets on your subdomain are served over HTTPS. Cloudflare offers "Automatic HTTPS Rewrites" and "Always Use HTTPS" Page Rule settings to help, but ideally, fix hardcoded HTTP links in your application.

 Incorrect Page Rule Order
*   Pitfall: A less specific Page Rule located higher up in the list might inadvertently override a more specific rule for your subdomain.
*   Result: Unintended caching behavior either too much or too little.
*   Solution: Always place more specific Page Rules e.g., for `subdomain.yourdomain.com/*` above broader rules e.g., for `yourdomain.com/*`. Cloudflare processes rules from top to bottom, and the first matching rule wins.

 Debugging `cf-cache-status: DYNAMIC`
*   Reason: Cloudflare didn't cache the resource because it detected it as dynamic. This often happens for HTML, or URLs with query strings, or if the `Cache-Control` header from the origin is missing or indicates non-cacheability.
*   Troubleshooting:
   1.  Check Origin Headers: Is your server sending appropriate `Cache-Control` headers for this resource?
   2.  Page Rule: If it's an HTML page you want to cache, apply a "Cache Everything" Page Rule for that specific URL or path.
   3.  Query Strings: If query strings are causing the issue, use the "Bypass Query String" option in a Page Rule or set "Caching Level: Cache Everything" which implicitly caches with query strings but verify this behavior.

 Purging Cache vs. Reloading
*   Pitfall: Making changes but not seeing them reflected, assuming Cloudflare isn't working.
*   Reason: Cloudflare and your browser might be serving a stale cached version.
*   Solution: Always perform a "Purge Cache" in the Cloudflare dashboard after making significant changes to your origin content or Cloudflare caching settings. For testing, use "Ctrl+Shift+R" hard refresh or "Cmd+Shift+R" on Mac, or clear your browser cache entirely.

 Time-to-Live TTL Settings
*   Pitfall: Setting `Edge Cache TTL` too high for frequently changing content, or too low for static content.
*   Result: Stale content served for too long, or excessive origin requests, defeating the purpose of caching.
*   Solution: Balance freshness and performance. For static assets images, CSS, JS, days or months are fine. For HTML, minutes or hours might be more appropriate, or use Cloudflare's `s-maxage` if your origin supports it to have longer Cloudflare cache and shorter browser cache.



By systematically approaching these potential pitfalls and utilizing the robust testing methods, you can ensure your subdomain caching is optimized, providing the best possible performance and reliability for your users.

# Security Considerations for Cached Subdomains

While caching significantly improves performance, it also introduces security considerations, especially for subdomains that might handle sensitive data or dynamic content. A misconfigured cache can inadvertently expose private information or serve incorrect data to users. Securing your cached subdomains involves more than just ensuring content is served fast. it's about serving the *right* content securely.

 Preventing Sensitive Data Exposure
*   Pitfall: Caching personalized pages, authenticated content, or pages containing sensitive user data e.g., order history, account details, API keys.
*   Risk: Another user could potentially see cached data belonging to someone else if the cache is not properly bypassed for authenticated requests.
*   Solution:
   *   Always use `Cache-Control: private` or `no-store` from your origin server for any page that contains user-specific or sensitive data.
   *   Implement "Bypass Cache on Cookie" or "Bypass Cache on Header" Page Rules: For example, if a user logs in and a specific session cookie is set, create a Page Rule for `*subdomain.yourdomain.com/*` with "Bypass Cache" if the cookie `session_id` exists. This ensures that only the unauthenticated, public version of the page if one exists is cached.
   *   Cloudflare Workers for Auth Logic: For advanced scenarios, use Cloudflare Workers to evaluate authentication tokens or cookies at the edge and conditionally bypass cache based on user status.

 Handling User-Generated Content UGC
*   Pitfall: Caching user-generated content e.g., comments, forum posts without proper sanitization or moderation.
*   Risk: Malicious users could inject harmful scripts XSS or inappropriate content into cached pages, which then get served to other users.
   *   Sanitize UGC at the Origin: Always sanitize and validate user input on your origin server *before* storing it and serving it.
   *   Moderate Content: Implement content moderation workflows.
   *   Purge Cache on Update: If UGC can be edited or deleted, ensure you have a mechanism e.g., via Cloudflare API to purge the specific URL from cache immediately after changes.

 Rate Limiting and DDoS Protection for Dynamic Subdomains
*   Pitfall: While caching offloads static content, dynamic subdomains e.g., APIs, login portals still hit your origin. These are vulnerable to brute-force attacks or DDoS if not protected.
*   Risk: Origin server overload, service disruption, account compromise.
   *   Cloudflare Rate Limiting: Apply Cloudflare Rate Limiting rules to dynamic endpoints on your subdomain e.g., `api.yourdomain.com/login`. This protects your origin from excessive requests.
   *   Cloudflare WAF Web Application Firewall: Enable WAF rules for your subdomain to protect against common web vulnerabilities SQL injection, XSS. Even if content is cached, WAF runs before cache lookup.
   *   Under Attack Mode: For severe attacks on dynamic subdomains, Cloudflare's "I'm Under Attack" mode can add an interstitial challenge, providing a powerful layer of protection.

 SSL/TLS Configuration
*   Pitfall: Using outdated SSL/TLS versions or weak cipher suites for your subdomain.
*   Risk: Vulnerability to eavesdropping, data interception, and compliance issues.
   *   Always Use HTTPS: Ensure your subdomain enforces HTTPS. Cloudflare's "Always Use HTTPS" Page Rule and SSL/TLS encryption modes Full, Full strict are crucial.
   *   Minimum TLS Version: Set the minimum TLS version to 1.2 or higher in Cloudflare's SSL/TLS settings to enforce modern encryption.
   *   HSTS HTTP Strict Transport Security: Implement HSTS for your subdomain via Cloudflare or origin to force browsers to always connect via HTTPS, preventing downgrade attacks. Cloudflare's "HSTS" setting in the SSL/TLS tab can pre-load your domain into browser HSTS lists.



By considering these security aspects, you transform your cached subdomain from just a performance booster into a resilient and secure part of your web infrastructure.

Remember, performance should never come at the cost of security.

# Monitoring and Analytics for Subdomain Performance



Effective management of cached subdomains goes beyond initial setup. it requires continuous monitoring and analysis.

Cloudflare provides a suite of analytics tools that offer invaluable insights into how your subdomains are performing, how efficiently they are being cached, and where bottlenecks might exist.

Regularly reviewing these metrics allows for proactive optimization and troubleshooting.

 Cloudflare Analytics Dashboard


Cloudflare's analytics dashboard is a treasure trove of data, providing a high-level overview of traffic, security, and performance.
1.  Overview Tab:
   *   Total Requests: See the total number of requests hitting your subdomain.
   *   Cached Requests vs. Uncached Requests: This is a crucial metric. A high percentage of cached requests the "Cache Ratio" indicates efficient caching. For example, if your subdomain is serving mostly static content, you might aim for a 85-95% cache ratio. If it's consistently low e.g., below 50% for static assets, it flags a caching issue.
   *   Bandwidth Saved: Shows how much bandwidth Cloudflare is saving your origin server by serving cached content. This translates directly to cost savings and reduced load on your server.
2.  Traffic Tab:
   *   Requests by Hostname: Filter data specifically for your subdomain e.g., `blog.yourdomain.com` to get its unique traffic profile.
   *   Requests by Content Type: See which types of content HTML, CSS, JS, images are most requested and how well each type is being cached. If images on your subdomain show a low cache ratio, it might indicate a problem with their `Cache-Control` headers.
3.  Performance Tab:
   *   Requests by Cache Status: Provides a breakdown of `HIT`, `MISS`, `DYNAMIC`, `BYPASS` requests. This directly correlates with your caching effectiveness. A high number of `MISS` or `DYNAMIC` requests for static content indicates configuration issues.
   *   Origin Performance: Shows the time Cloudflare takes to connect to your origin server for uncached requests. High origin response times suggest your server might be struggling or needs optimization.

 Interpreting Metrics and Taking Action
*   Low Cache Ratio for Static Content:
   *   Action: Check your origin server's `Cache-Control` headers for those specific content types. Are they sending `no-cache` or very short `max-age` values?
   *   Action: Review Cloudflare Page Rules for the subdomain. Is there a "Cache Everything" rule with an appropriate `Edge Cache TTL`? Is it correctly ordered?
   *   Action: Ensure the DNS record for the subdomain is proxied orange cloud.
*   High `DYNAMIC` or `BYPASS` Requests for Content You Expect to Cache:
   *   Action: This often points to URLs with query strings or misidentified content. Apply a "Cache Everything" Page Rule, potentially combined with "Bypass Query String Cache" if query strings don't alter content.
   *   Action: Verify if the `cf-cache-status` is `BYPASS` due to a custom header or a specific Page Rule you might have forgotten.
*   Spikes in Origin Requests:
   *   Action: Could indicate a cache purge, a misconfiguration, or an increase in dynamic traffic. Investigate the cause.
   *   Action: Review your cache TTLs – are they too short for the traffic volume?

 Setting Up Cloudflare Alerts


Cloudflare allows you to set up alerts for various metrics, ensuring you're notified of critical changes.
*   Cache Ratio Drop: Set an alert if the cache ratio for your subdomain drops below a certain threshold e.g., 60% for static sites.
*   Origin Error Rate: Monitor your origin server's error rate. If Cloudflare starts seeing more 5xx errors from your subdomain's origin, it can indicate problems.
*   Spikes in Uncached Requests: Get notified if there's an unusual surge in requests hitting your origin server for the subdomain.



By regularly monitoring these metrics and setting up appropriate alerts, you can maintain optimal performance and quickly address any caching inefficiencies or issues related to your subdomains, ensuring a smooth and efficient user experience.

This proactive approach is fundamental to leveraging Cloudflare's full potential.

 Frequently Asked Questions

# What does "Cloudflare bypass cache for subdomain" mean?


"Cloudflare bypass cache for subdomain" generally refers to situations where traffic for a specific subdomain is not being served from Cloudflare's cache, but instead is directly routed to your origin server.

This can be intentional e.g., for highly dynamic content or unintentional due to misconfigurations.

# How do I check if my subdomain is being cached by Cloudflare?


You can check if your subdomain is being cached by Cloudflare using browser developer tools Network tab or command-line tools like `curl`. Look for the `cf-cache-status` response header. If it says `HIT`, it's cached.

If it's `MISS`, `DYNAMIC`, or `BYPASS`, it's not being served from cache.

# Why is my Cloudflare subdomain not caching?


Your Cloudflare subdomain might not be caching due to several reasons: incorrect DNS proxy status grey cloud, origin server sending `Cache-Control: no-cache` or `no-store` headers, conflicting Cloudflare Page Rules, dynamic content with query strings, or the specific file types not being part of Cloudflare's default cacheable extensions.

# What is the most common reason for a subdomain cache bypass?


The most common reason for a subdomain cache bypass is the origin server sending `Cache-Control: no-cache` or `max-age=0` headers, which Cloudflare respects by default.

Another frequent cause is the subdomain's DNS record in Cloudflare being set to "DNS Only" grey cloud instead of "Proxied" orange cloud.

# How do I force Cloudflare to cache everything for a subdomain?
To force Cloudflare to cache everything for a subdomain, you can create a Cloudflare Page Rule. Set the URL pattern to `*subdomain.yourdomain.com/*` and choose the "Caching Level: Cache Everything" setting. Remember to set an appropriate "Edge Cache TTL" as well.

# Can Cloudflare cache dynamic content for a subdomain?


Yes, Cloudflare can cache dynamic content for a subdomain using the "Caching Level: Cache Everything" Page Rule.

However, this should be used with extreme caution to avoid serving stale or personalized content to the wrong users.

It's often better to cache only static assets or rely on Cloudflare Workers for conditional dynamic caching.

# What is Edge Cache TTL in Cloudflare and how does it affect subdomains?


Edge Cache TTL Time To Live in Cloudflare determines how long Cloudflare's edge servers will store a cached resource for your subdomain before it needs to re-fetch it from your origin server.

Setting an appropriate TTL is crucial for balancing content freshness and performance.

# How do I purge Cloudflare cache for a specific subdomain?
You can purge Cloudflare cache for a specific subdomain by navigating to Caching > Configuration in your Cloudflare dashboard. Use the "Custom Purge" option and enter `subdomain.yourdomain.com/*` to clear all cached content for that subdomain.

# Should I set `Cache-Control` headers on my origin server if I use Cloudflare?


Yes, it is highly recommended to set appropriate `Cache-Control` headers on your origin server even if you use Cloudflare.

Cloudflare respects these headers by default, providing a strong foundation for your caching strategy and ensuring consistent behavior across different caching layers.

# What is the difference between `cf-cache-status: DYNAMIC` and `cf-cache-status: BYPASS`?


`cf-cache-status: DYNAMIC` indicates that Cloudflare determined the content was dynamic and did not cache it by default often due to query strings or HTML. `cf-cache-status: BYPASS` means that caching was explicitly prevented, usually by a Cloudflare Page Rule e.g., "Bypass Cache" setting or an `X-Cache-Control` header from your origin.

# Can I bypass cache for a subdomain only for authenticated users?


Yes, you can bypass cache for a subdomain only for authenticated users.

This is typically done using Cloudflare Page Rules with the "Bypass Cache on Cookie" or "Bypass Cache on Header" settings, which instruct Cloudflare to bypass cache if a specific authentication cookie or header is present in the request.

# How many Page Rules do I get for free on Cloudflare?


Cloudflare's free plan typically includes up to 3 Page Rules per domain.

If you need more granular control or additional rules for multiple subdomains, you would need to upgrade to a paid plan.

# Does Cloudflare cache HTML pages by default for subdomains?


No, Cloudflare's "Standard" caching level does not cache HTML pages by default for subdomains or main domains. It primarily caches static assets like CSS, JavaScript, and images.

To cache HTML, you need to use a "Cache Everything" Page Rule.

# What are the risks of caching too much content on a subdomain?


The risks of caching too much content on a subdomain include serving stale content, exposing personalized or sensitive user data, and potential security vulnerabilities if user-generated content is cached without proper sanitization.

It's crucial to balance performance with content freshness and security.

# How do Cloudflare Workers help with subdomain caching?


Cloudflare Workers allow you to write custom JavaScript code that runs at Cloudflare's edge.

This enables highly advanced and conditional caching logic for subdomains, such as caching based on request headers, cookies, or specific URL patterns that aren't possible with standard Page Rules.

# Can I use Cloudflare's HSTS for my subdomain to enforce HTTPS?


Yes, you can and should use Cloudflare's HSTS HTTP Strict Transport Security settings for your subdomain to enforce HTTPS.

This instructs browsers to always connect to your subdomain via HTTPS, preventing insecure HTTP connections and enhancing security.

You can configure this under the SSL/TLS section in your Cloudflare dashboard.

# How does the "Development Mode" affect subdomain caching?


Cloudflare's "Development Mode" temporarily bypasses Cloudflare's cache and other performance features for your entire domain including subdomains. This is useful for development purposes when you want to see changes to your origin server immediately without waiting for cache invalidation. Remember to turn it off when done.

# What should I do if my subdomain's images are not caching?


If your subdomain's images are not caching, first check the `Cache-Control` headers sent by your origin server for those images.

Ensure they have a `public` directive and a reasonable `max-age`. Also, confirm that the image file types e.g., `.jpg`, `.png` are part of Cloudflare's default cacheable extensions or that a "Cache Everything" Page Rule is applied to the image paths.

# Does the order of Page Rules matter for subdomain caching?
Yes, the order of Page Rules matters significantly.

Cloudflare processes Page Rules from top to bottom, and the first rule that matches a request URL will be applied.

Therefore, more specific rules e.g., for a specific subdomain or path should be placed above broader rules that might otherwise override them.

# What is the `s-maxage` directive and how can it be used with Cloudflare for subdomains?


The `s-maxage` directive in the `Cache-Control` header is similar to `max-age` but applies specifically to shared caches like Cloudflare's edge servers. You can use `s-maxage` to tell Cloudflare to cache content for a longer duration e.g., `s-maxage=86400` for 24 hours while simultaneously using `max-age` for a shorter duration for client browsers e.g., `max-age=3600` for 1 hour. This allows you to have a long cache at the edge but serve fresh content to users more frequently.

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