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Hosting the AMP framework
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hosting-amp-framework.md

Documentation Moved
This guide is now available from the AMP Project at:
https://github.com/ampproject/amphtml/blob/main/docs/spec/amp-framework-hosting.md
No further updates are planned for this gist, so please use the official documentation going forward.

Hosting the AMP framework

You can host the AMP framework and components from your own server or CDN. This feature has a number of applications. For example, you can...

  • set a release cadence that matches your development cycle.
  • deliver the AMP framework in regions where cdn.ampproject.org may not be available.
  • serve AMP pages and the framework from the same host, potentially improving content delivery times.
  • test and demonstrate changes to the framework or components.

The AMP Project is looking into options for validation of AMP pages that use an AMP framework hosted outside of cdn.ampproject.org (#27546). As of April 2020, these AMP pages do not pass validation.

Versioning

This document makes frequent use of the terms "version" and "runtime version (rtv)". These two versions are slightly different. When the AMP framework is built, it is assigned a 13-digit version. When the AMP framework is served, a config number prefixes the version, resulting in a 15-digit runtime version. The build system and runtime enforce these version formats.

Note: The version (sometimes referred to as the "AMP version number") and runtime version are often confused with each other. When it matters, be explicit about the version to which you're referring by indicating 13- or 15-digits.

When the AMP framework is built (either by you or by the AMP Project), a 13-digit date-based version is automatically assigned. You can find this version in version.txt at the root of the AMP framework distribution. Then, the easiest route to hosting the AMP framework is to prefix this version with 01 to create a 15-digit runtime version, where 01 indicates a stable release.

A more complete picture of the conventions adopted by the AMP Project for the version and runtime version is below. This is more than you need to get started with hosting the AMP framework, but serves as a good reference in case you want to expand your hosting capabilities.

  • Version (#16631 and #27848): the commit time of the last commit in the active branch

    TZ=UTC git log -1 --pretty="%cd" --date=format-local:%y%m%d%H%M

    with three trailing digits indicating the number of cherry-picks included in the release. This version corresponds to the release versions found on github.com/ampproject/amphtml/releases.

    Note: Prior to 2020-04-25, the version was based on date/time format %y%m%d%H%M%S with a single trailing digit – typically 0, but could be change arbitrarily.

  • Runtime version (rtv): the version prefixed by a 2-digit config code:

    • Experimental: 00
    • Stable: 01
    • Control: 02
    • Beta: 03
    • Nightly: 04
    • Nightly-Control: 05
    • AMP Experiments: 10, 11, 12
    • INABOX Control and Experiments: 20, 21, 22, 23, 24, 25

The runtime version is found in URLs and is reported in the console of browser inspectors when an AMP page loads. For example, runtime version 012004041903580 is stable version 2004041903580.

Acquire the AMP framework

The AMP framework can be built from source or downloaded pre-built. Building the framework yourself gives you the flexibility of modifying the framework for your needs and deploying changes on your own release cycle. Downloading a pre-built framework means you'll be using an unmodified release, vetted by the AMP Project for distribution.

Option 1: Build the framework yourself

Refer to the Developing in AMP guide to familiarize yourself with building and testing the AMP framework. Once you are comfortable with the build system, a few small changes will customize the framework to run from your host.

Update URLs config

When AMP is built, several scripts are prepended with an AMP_CONFIG environment variable (object) containing basic information like: runtime version, config type, experiment enable/disable status, etc. This object can be customized at build time to inform the runtime where the framework is hosted. See build-system/global-configs/README.md for information about the custom-config.json overlay.

Create JSON file build-system/global-configs/custom-config.json with the following contents:

{
  "cdnUrl": "https://example.com/amp-framework",
  "geoApiUrl": "https://example.com/geo-api"
}

where

  • cdnUrl is the base URL to your AMP framework. Defaults to https://cdn.ampproject.org.
  • geoApiUrl (optional) is your amp-geo fallback API URL. This API is described in section amp-geo hotpatching. Defaults to null.

Important: build-system/global-configs/custom-config.json is not part of checked-in source. If it exists, it always applies at build time, overlaying the active config. Don't forget about it! You can verify the overlay applies by looking for log line Overlaid config with custom-config.json during the build process.

Build the framework

Build an AMP release with

gulp dist

The built framework can be found in directory dist. The version assigned to the build is in dist/version.txt and a listing of all files included in build is in dist/files.txt. The framework is ready to be moved to and served from your host.

If you have advanced hosting capabilities or would like to manually assign a version, gulp dist accepts these flags (among others):

  • --config: Indicate the release type, production (prod) or canary (canary). Defaults to prod.
  • --version_override: Assign a version to the distribution. The version must consist of 13-digits. Defaults to the latest git commit time of the active branch.
  • --sourcemap_url: Provide the base URL for JavaScript source map links. This URL should contain placeholder {version} that will be replaced with the actual version when the AMP framework is built, for example https://raw.githubusercontent.com/<github-username>/amphtml/{version}/. Defaults to https://raw.githubusercontent.com/ampproject/amphtml/{version}/.

Option 2: Download the framework with an AMP Toolbox tool

AMP Toolbox has both a Node.js module and a command line tool that will fetch a complete AMP framework from cdn.ampproject.org. Pick the tool best suited to your release workflow.

Option 3: Manually copy the framework from cdn.ampproject.org

The AMP framework can be copied from cdn.ampproject.org. The latest weekly release is always served from the root of cdn.ampproject.org. All non-deprecated releases can be found in versioned URLs: cdn.ampproject.org/rtv/<rtv>, where <rtv> is the runtime version.

Note: The AMP Project is looking into options for packaging releases (#27726).

Copy files

A listing of files in each release can be found in files.txt at the root of the framework distribution. For example, the files included in the current weekly release are listed in cdn.ampproject.org/files.txt. Use your favorite HTTP client to download all of the files in files.txt, retaining path structures.

Undo amp-geo dynamic modification

When you request amp-geo-0.1.js from cdn.ampproject.org using an HTTP client, the CDN detects the country where the request originated and patches amp-geo-0.1.js on-the-fly. This patch needs to be reversed to ensure users are not all assigned the same country when amp-geo loads.

When cdn.ampproject.org serves amp-geo-0.1.js, it replaces string {{AMP_ISO_COUNTRY_HOTPATCH}} with an ISO 3166-1 country code or an ISO 3166-2 country-subdivision code, followed by enough spaces to maintain the length of the string being replaced. Reversal of this patch can be accomplished by a RegEx replacement: search for / {28}|[a-z]{2} {26}|[a-z]{2} [a-z]{2}-[a-z0-9]{1,3} {19,21}/i and replace with {{AMP_ISO_COUNTRY_HOTPATCH}}.

In addition to amp-geo-0.1.js, you may find module JS (.mjs) and unversioned (amp-geo-latest.js) variants of the same file. The same RegEx replacement should be performed in these files as well.

Modify AMP pages

AMP pages should be updated to fetch all scripts from your host. For example,

<script async src="https://cdn.ampproject.org/v0.js"></script>
<script async custom-element="amp-carousel" src="https://cdn.ampproject.org/v0/amp-carousel-0.1.js"></script>

becomes

<script async src="https://example.com/amp/v0.js"></script>
<script async custom-element="amp-carousel" src="https://example.com/amp/v0/amp-carousel-0.1.js"></script>

Versioned URLs are also possible and discussed in section Serve the AMP framework.

Important: All scripts must come from the same origin. Fetching scripts from multiple origins is not supported and can lead to unpredictable end user experiences.

Meta tags

If you opted to download the AMP framework, then it was built under the assumption that it would be hosted from its default location, cdn.ampproject.org. While <script> tags included in the <head> of your AMP pages will download from the URLs specified in their src attributes, dynamically loaded components like amp-loader-0.1.js will download from cdn.ampproject.org. Mixing a self-hosted AMP runtime with AMP components from cdn.ampproject.org is not supported and can lead to unpredictable end user experiences.

The default host used by the AMP runtime can be updated by including the following <meta> tag in the <head> of your AMP pages:

<meta name="runtime-host" content="...">

where the content attribute should contain a URL to your hosted AMP framework. Similarly, an amp-geo fallback API URL (described in section amp-geo hotpatching) can be defined with the following <meta> tag:

<meta name="amp-geo-api" content="...">

In each case, the value of the content attribute should be an absolute, HTTPS URL. Importantly, these meta tags must appear before the first <script> tag. For example, if your AMP framework is hosted at https://example.com/amp, then your <head> should look similar to the following:

<head>
  ...
  <!-- This instructs the AMP runtime to update its default host -->
  <meta name="runtime-host" content="https://example.com/amp">

  <!-- (Optional) This provides a fallback API for amp-geo -->
  <meta name="amp-geo-api" content="https://example.com/geo/get-country">

  <!-- All scripts appear after the above meta tags -->
  <script async src="https://example.com/amp/v0.js"></script>
  <script async custom-element="amp-geo" src="https://example.com/amp/v0/amp-geo-0.1.js"></script>
</head>

Serve the AMP framework

Depending on your hosting capabilities and goals, there are several options to consider when serving the AMP framework.

URLs

When the AMP runtime is initialized, all components are verified to belong to the same AMP framework version as the runtime itself. This affects components that have already downloaded as well as components that are downloaded dynamically, like amp-loader. Dynamic components and components with incorrect versions are (re-)downloaded from an rtv-specific path. This has consequences on how you choose to host the runtime.

Versioned URLs

The simplest option for hosting the AMP framework is to host it from an rtv-specific path. For example, consider AMP framework host https://example.com/amp. Stable version 2002290616360 corresponds to runtime version 012002290616360 and should be hosted from https://example.com/amp/rtv/012002290616360. In this case, AMP meta and script URLs would look like the following:

<meta name="runtime-host" content="https://example.com/amp"> <!-- not rtv-specific -->
<script async src="https://example.com/amp/rtv/012002290616360/v0.js"></script>
<script async custom-element="amp-geo" src="https://example.com/amp/rtv/012002290616360/v0/amp-geo-0.1.js"></script>

If hosting a single AMP framework version is your end goal, then you can update your AMP pages to download the runtime and components from your host and skip to section amp-geo hotpatching. If you expect to update the AMP framework regularly, then updating rtv-specific URLs in AMP pages could be cumbersome. See the next section, Versionless URLs, for a solution.

Versionless URLs

The AMP Project has a weekly release channel, sometimes referred to as the "evergreen" release channel. AMP pages utilize this channel by including versionless URLs to AMP scripts and styles. This is relatively easy to accomplish when hosting the AMP framework yourself. The key is to ensure that the AMP framework hosted from versionless URLs is also available from rtv-specific URLs. This suggests an update strategy: first make a new AMP framework version available from rtv-specific URLs and then update the AMP framework available from versionless URLs. For example, if stable AMP framework version 2002290616360 is available from https://example.com/amp, then it must also be available from https://example.com/amp/rtv/012002290616360. In this case, AMP meta and script URLs would look like the following:

<meta name="runtime-host" content="https://example.com/amp">
<script async src="https://example.com/amp/v0.js"></script>
<script async custom-element="amp-geo" src="https://example.com/amp/v0/amp-geo-0.1.js"></script>

If you inspect the DOM after an AMP page loads, you'll notice additional components are dynamically loaded by the runtime and use versioned URLs, for example

<script async custom-element="amp-auto-lightbox" data-script="amp-auto-lightbox" i-amphtml-inserted crossorigin="anonymous" src="https://example.com/amp/rtv/012002290616360/v0/amp-auto-lightbox-0.1.js"></script>

Metadata

The AMP Project hosts a metadata endpoint at cdn.ampproject.org/rtv/metadata that returns information on current releases. Hosting this endpoint yourself is optional, but may be useful if you use AMP Toolbox:

Consider the following sample from cdn.ampproject.org/rtv/metadata, most JSON properties are optional:

{
  "ampRuntimeVersion": "012002192257490",
  "ampCssUrl": "https://cdn.ampproject.org/rtv/012002192257490/v0.css",
  "canaryPercentage": "0.005",
  "diversions": ["002002251816300", "032002251816300", "022002192257490"],
  "ltsRuntimeVersion": "012002191527100",
  "ltsCssUrl": "https://cdn.ampproject.org/rtv/012002191527100/v0.css"
}

The properties are defined as follows:

  • ampRuntimeVersion (required) is the current stable runtime version of the AMP framework.
  • ampCssUrl (optional) is a URL to the boilerplate CSS for the current stable runtime version.
  • canaryPercentage (optional) indicates the fraction of users who receive the experimental runtime version of the AMP framework instead of the current stable runtime version.
  • diversions (optional) lists active non-stable runtime versions.
  • ltsRuntimeVersion (optional) is the current long-term stable runtime version.
  • ltsCssUrl (optional) is a URL to the boilerplate CSS for the current long-term stable runtime version.

amp-geo hotpatching

amp-geo requires special attention when hosting the AMP framework. When cdn.ampproject.org serves any of amp-geo-0.1.js, amp-geo-0.1.mjs, amp-geo-latest.js, or amp-geo-latest.mjs, it detects the country and subdivision where the request originated and replaces string {{AMP_ISO_COUNTRY_HOTPATCH}} with region data and enough trailing spaces to maintain the original string length. Ideally, when hosting the AMP framework, your content distribution platform would perform the same manipulation. The logic is as follows:

  • If country could not be determined, substitute 28 spaces: 
    Before: "{{AMP_ISO_COUNTRY_HOTPATCH}}"
After:  "                            "
  • If country could be determined, substitute the ISO 3166-1 alpha-2 country code followed by 26 spaces: 
    Before: "{{AMP_ISO_COUNTRY_HOTPATCH}}"
After:  "xx                          "
    where xx is the country code (e.g. de for Germany).
  • If country and subdivision could be determined and are exactly us (United States) and ca (California), respectively (this is the only subdivision supported by amp-geo as of this writing), substitute the ISO 3166-1 alpha-2 country code and the ISO 3166-2 country-subdivision code followed by 20 spaces: 
    Before: "{{AMP_ISO_COUNTRY_HOTPATCH}}"
After:  "us us-ca                    "

amp-geo fallback API

If location detection and file modification at time of delivery are not possible, amp-geo supports use of an API to fetch the user's country at run time. Be aware that usage of an API for this feature increases the chances of visible content or style shifts due to the delay of an additional network request. The AMP Project does not provide this API service; you need to supply your own API. Two example providers (not a comprehensive list) that offer IP-to-country databases from which an API could be created include MaxMind and IP2Location.

The API must meet the following requirements:

  • Satisfy CORS security in AMP
  • Be secure (HTTPS)
  • Return application/json content conforming to the following schema: 
    {
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "properties": {
    "country": {
      "type": "string",
      "title": "ISO 3166-1 alpha-2 (case insensitive) country code of client request",
      "default": "",
      "pattern": "^[a-zA-Z]{2}$"
    },
    "subdivision": {
      "type": "string",
      "title": "Subdivision part of ISO 3166-2 (case insensitive) country-subdivision code of client request",
      "default": "",
      "pattern": "^[a-zA-Z0-9]{1,3}$"
    }
  },
  "required": [
    "country"
  ]
}

A sample response for a user in Germany looks like:

{
  "country": "de"
}

A sample response for a user in California, US looks like:

{
  "country": "us",
  "subdivision": "ca"
}

Note: As of April 2020, us-ca is the only subdivision supported by amp-geo.

There are trade-offs in accuracy and performance when you set the client cache time for this API. Longer cache times are better for performance on subsequent page loads but can lead to incorrect country detection. For reference, https://cdn.ampproject.org/v0/amp-geo-0.1.js has a client cache time of 30 minutes.

HTTP response headers

In addition to following TLS best practices, consider the following headers when hosting the AMP framework:

  • content-security-policy: If your pages implement AMP's CSP, apply a matching content security policy to your hosted framework responses. Inspect the headers on https://cdn.ampproject.org/v0.js for a base policy that should be expanded to include resources served from your host.

  • access-control-allow-origin: Some runtime components are fetched via XHR. If your AMP pages will be served from a different host than your framework, be sure to include CORS headers (see also CORS Requests in AMP).

  • content-type: There are a few resources served without file extensions, or with extensions that may not be recognized by all web servers. In addition to common types, you may want to include special handling for the following:

    • /rtv/metadata - application/json
    • /amp_preconnect_polyfill_404_or_other_error_expected._Do_not_worry_about_it - text/html

    A complete list of files in each AMP release can be found in files.txt, for example https://cdn.ampproject.org/files.txt.

  • cache-control: The AMP framework hosted from versioned URLs should be "immutable"; users should expect to find the same content from these URLs for as long as the URLs are active (amp-geo is an exception, see below). Long cache times are appropriate. On the other hand, the AMP framework hosted from versionless URLs should be served with relatively short cache times so that minimal time is required for your latest update to reach all users.

    • Versioned URL example: cdn.ampproject.org sets a 1 year client cache time on resources served under cdn.ampproject.org/rtv/<rtv>: cache-control: public, max-age=31536000.
    • Versionless URL example: cdn.ampproject.org sets a 50 minute client cache time for resources served from versionless URLs, but also allows a long 2 week stale-while-revalidate time in the event that versionless URLs experience an outage: cache-control: private, max-age=3000, stale-while-revalidate=1206600.
    • amp-geo-*.(m)js: If amp-geo hotpatching is utilized, there is a trade-off in accuracy and performance when you set this cache time. Longer cache times are better for performance on subsequent page loads but can lead to incorrect country detection. Both cdn.ampproject.org/v0/amp-geo-0.1.js and cdn.ampproject.org/rtv/<rtv>/v0/amp-geo-0.1.js set the client cache time to 30 minutes.
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