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Cache using fetch

Determine how to cache a resource by setting TTLs, custom cache keys, and cache headers in a fetch request.

export default {
  async fetch(request) {
    const url = new URL(request.url);
    // Only use the path for the cache key, removing query strings
    // and always store using HTTPS, for example, https://www.example.com/file-uri-here
    const someCustomKey = `https://${url.hostname}${url.pathname}`;
    let response = await fetch(request, {
      cf: {
        // Always cache this fetch regardless of content type
        // for a max of 5 seconds before revalidating the resource
        cacheTtl: 5,
        cacheEverything: true,
        //Enterprise only feature, see Cache API for other plans
        cacheKey: someCustomKey,
      },
    });
    // Reconstruct the Response object to make its headers mutable.
    response = new Response(response.body, response);
    // Set cache control headers to cache on browser for 25 minutes
    response.headers.set("Cache-Control", "max-age=1500");
    return response;
  },
};

Caching HTML resources

// Force Cloudflare to cache an asset
fetch(event.request, { cf: { cacheEverything: true } });

Setting the cache level to Cache Everything will override the default cacheability of the asset. For time-to-live (TTL), Cloudflare will still rely on headers set by the origin.

Custom cache keys

A request’s cache key is what determines if two requests are the same for caching purposes. If a request has the same cache key as some previous request, then Cloudflare can serve the same cached response for both. For more about cache keys, refer to the Create custom cache keys documentation.

// Set cache key for this request to "some-string".
fetch(event.request, { cf: { cacheKey: "some-string" } });

Normally, Cloudflare computes the cache key for a request based on the request’s URL. Sometimes, though, you may like different URLs to be treated as if they were the same for caching purposes. For example, if your website content is hosted from both Amazon S3 and Google Cloud Storage - you have the same content in both places, and you can use a Worker to randomly balance between the two. However, you do not want to end up caching two copies of your content. You could utilize custom cache keys to cache based on the original request URL rather than the subrequest URL:

export default {
  async fetch(request) {
    let url = new URL(request.url);


    if (Math.random() < 0.5) {
      url.hostname = "example.s3.amazonaws.com";
    } else {
      url.hostname = "example.storage.googleapis.com";
    }


    let newRequest = new Request(url, request);
    return fetch(newRequest, {
      cf: { cacheKey: request.url },
    });
  },
};

Workers operating on behalf of different zones cannot affect each other’s cache. You can only override cache keys when making requests within your own zone (in the above example event.request.url was the key stored), or requests to hosts that are not on Cloudflare. When making a request to another Cloudflare zone (for example, belonging to a different Cloudflare customer), that zone fully controls how its own content is cached within Cloudflare; you cannot override it.

Override based on origin response code

// Force response to be cached for 86400 seconds for 200 status
// codes, 1 second for 404, and do not cache 500 errors.
fetch(request, {
  cf: { cacheTtlByStatus: { "200-299": 86400, 404: 1, "500-599": 0 } },
});

This option is a version of the cacheTtl feature which chooses a TTL based on the response’s status code and does not automatically set cacheEverything: true. If the response to this request has a status code that matches, Cloudflare will cache for the instructed time, and override cache directives sent by the origin. You can review details on the cacheTtl feature on the Request page.

Customize cache behavior based on request file type

Using custom cache keys and overrides based on response code, you can write a Worker that sets the TTL based on the response status code from origin, and request file type.

The following example demonstrates how you might use this to cache requests for streaming media assets:

index.js
export default {
  async fetch(request) {
    // Instantiate new URL to make it mutable
    const newRequest = new URL(request.url);


    const customCacheKey = `${newRequest.hostname}${newRequest.pathname}`;
    const queryCacheKey = `${newRequest.hostname}${newRequest.pathname}${newRequest.search}`;


    // Different asset types usually have different caching strategies. Most of the time media content such as audio, videos and images that are not user-generated content would not need to be updated often so a long TTL would be best. However, with HLS streaming, manifest files usually are set with short TTLs so that playback will not be affected, as this files contain the data that the player would need. By setting each caching strategy for categories of asset types in an object within an array, you can solve complex needs when it comes to media content for your application


    const cacheAssets = [
      {
        asset: "video",
        key: customCacheKey,
        regex:
          /(.*\/Video)|(.*\.(m4s|mp4|ts|avi|mpeg|mpg|mkv|bin|webm|vob|flv|m2ts|mts|3gp|m4v|wmv|qt))/,
        info: 0,
        ok: 31556952,
        redirects: 30,
        clientError: 10,
        serverError: 0,
      },
      {
        asset: "image",
        key: queryCacheKey,
        regex:
          /(.*\/Images)|(.*\.(jpg|jpeg|png|bmp|pict|tif|tiff|webp|gif|heif|exif|bat|bpg|ppm|pgn|pbm|pnm))/,
        info: 0,
        ok: 3600,
        redirects: 30,
        clientError: 10,
        serverError: 0,
      },
      {
        asset: "frontEnd",
        key: queryCacheKey,
        regex: /^.*\.(css|js)/,
        info: 0,
        ok: 3600,
        redirects: 30,
        clientError: 10,
        serverError: 0,
      },
      {
        asset: "audio",
        key: customCacheKey,
        regex:
          /(.*\/Audio)|(.*\.(flac|aac|mp3|alac|aiff|wav|ogg|aiff|opus|ape|wma|3gp))/,
        info: 0,
        ok: 31556952,
        redirects: 30,
        clientError: 10,
        serverError: 0,
      },
      {
        asset: "directPlay",
        key: customCacheKey,
        regex: /.*(\/Download)/,
        info: 0,
        ok: 31556952,
        redirects: 30,
        clientError: 10,
        serverError: 0,
      },
      {
        asset: "manifest",
        key: customCacheKey,
        regex: /^.*\.(m3u8|mpd)/,
        info: 0,
        ok: 3,
        redirects: 2,
        clientError: 1,
        serverError: 0,
      },
    ];


    const { asset, regex, ...cache } =
      cacheAssets.find(({ regex }) => newRequest.pathname.match(regex)) ?? {};


    const newResponse = await fetch(request, {
      cf: {
        cacheKey: cache.key,
        polish: false,
        cacheEverything: true,
        cacheTtlByStatus: {
          "100-199": cache.info,
          "200-299": cache.ok,
          "300-399": cache.redirects,
          "400-499": cache.clientError,
          "500-599": cache.serverError,
        },
        cacheTags: ["static"],
      },
    });


    const response = new Response(newResponse.body, newResponse);


    // For debugging purposes
    response.headers.set("debug", JSON.stringify(cache));
    return response;
  },
};
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