Control origin requests with a policy - Amazon CloudFront

Control origin requests with a policy

When a viewer request to CloudFront results in a cache miss (the requested object is not cached at the edge location), CloudFront sends a request to the origin to retrieve the object. This is called an origin request. The origin request always includes the following information from the viewer request:

  • The URL path (the path only, without URL query strings or the domain name)

  • The request body (if there is one)

  • The HTTP headers that CloudFront automatically includes in every origin request, including Host, User-Agent, and X-Amz-Cf-Id

Other information from the viewer request, such as URL query strings, HTTP headers, and cookies, is not included in the origin request by default. (Exception: With legacy cache settings, CloudFront forwards the headers to your origin by default.) However, you might want to receive some of this other information at the origin, for example to collect data for analytics or telemetry. You can use an origin request policy to control the information that's included in an origin request.

Origin request policies are separate from cache policies, which control the cache key. This way, you can receive additional information at the origin and also maintain a good cache hit ratio (the proportion of viewer requests that result in a cache hit). You do this by separately controlling which information is included in origin requests (using the origin request policy) and which is included in the cache key (using the cache policy).

Although the two kinds of policies are separate, they are related. All URL query strings, HTTP headers, and cookies that you include in the cache key (using a cache policy) are automatically included in origin requests. Use the origin request policy to specify the information that you want to include in origin requests, but not include in the cache key. Just like a cache policy, you attach an origin request policy to one or more cache behaviors in a CloudFront distribution.

You can also use an origin request policy to add additional HTTP headers to an origin request that were not included in the viewer request. These additional headers are added by CloudFront before sending the origin request, with header values that are determined automatically based on the viewer request. For more information, see Add CloudFront request headers.

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