• websites

Using the Google AMP Cache

Introduction

The Google AMP Cache stores valid AMPs and provides a consistently fast access to AMPs. It is available for anyone to use.

AMP Cache URL Format

When possible, the Google AMP Cache will create a subdomain for each AMP document's domain by first converting it from IDN (punycode) to UTF-8. The caches replaces every - (dash) with -- (2 dashes) and replace every . (dot) with - (dash). For example, pub.com will map to pub-com.cdn.ampproject.org.

Here is AMP Cache URL for https://amp.dev/about/websites/:

The converted AMP Cache URL consists of the following parts:

• amp-dev: the publisher domain converted into a subdomain using the algorithm described above.
• cdn.ampproject.org: the AMP Cache domain.
• c: to indicate that it's an AMP document (there is also i for image and r for resources such as fonts).
• s: indicating that the AMP Cache fetches the content from the origin using TLS (secure HTTPS).
• amp.dev/examples/components/amp-img: the original URL excluding the scheme.

It is OK for URLs to include parameters in the query string, simply include these in the AMP Cache URL as well.

Example: https://amp-dev.cdn.ampproject.org/c/s/amp.dev/documentation/examples/api/query?value=Hello%20World.

Cache updates

The AMP Cache uses a one-behind caching model which can be controlled by the max-age cache directive. You can test the behavior with this sample page, which will prints the current date at serving time:

Max-age 15s: https://amp-dev.cdn.ampproject.org/c/s/amp.dev/documentation/examples/api/query?maxage=15.

Redirect & Error Handling

Here are some examples for how the AMP Cache handles redirects and errors:

Redirects

The AMP Cache follows redirects when resolving AMP URLs. For example, if an URL redirects to another AMP URL:

$ curl -I https://ampbyexample.com/components/amp-img/

HTTP/1.1 301 Moved Permanently
Content-Type: text/html; charset=utf-8
Location: https://amp.dev/documentation/examples/components/amp-img/
...

Then the AMP Cache will return the content of the resolved redirect for the original URL.

Example: https://amp-dev.cdn.ampproject.org/c/s/ampbyexample.com/components/amp-img/.

Not Found

When a page is not found in the AMP Cache, it will show an error page and return a 404 status.

Example: https://amp-dev.cdn.ampproject.org/amp.dev/not-found

Invalid AMP

When a page is invalid AMP, the AMP Cache will return a 404 status.

Example: https://amp-dev.cdn.ampproject.org/amp.dev/static/samples/files/invalid_amp.html

Server Errors

If an URL returns a 5XX server errors, the AMP Cache will return a 404 status.

Example: https://amp-dev.cdn.ampproject.org/amp.dev/documentation/examples/api/error

• Written by @kul3r4