Rendertron-slim

Rendertron is a headless Chrome rendering solution designed to render & serialise web pages on the fly.

🔨 Built with Puppeteer

Contents

• API
  • Render
  • Screenshot
• FAQ
  • Page render timing
  • Rendering budget timeout
  • Web components
  • Status codes
• Installing & deploying
  • Building
  • Config

API

Rendertron-slim uses a GRPC API. Docs and GRPC the schema are availabe at: buf.build/nemoengineering/rendertron

Render()

The render endpoint will render your page and serialize your page.

Screenshot()

The screenshot endpoint takes an screenshot of the page provided in the URL

Page render timing

The service attempts to detect when a page has loaded by looking at the page load event, ensuring there are no outstanding network requests and that the page has had ample time to render.

Rendering budget timeout

There is a hard limit of 10 seconds for rendering. Ensure you don't hit this budget by ensuring your application is rendered well before the budget expires.

Web components

index.ts Headless Chrome supports web components but shadow DOM is difficult to serialize effectively. As such, shady DOM (a lightweight shim for Shadow DOM) is required for web components.

If you are using web components v0 (deprecated), you will need to enable Shady DOM to render correctly. In Polymer 1.x, which uses web components v0, Shady DOM is enabled by default. If you are using Shadow DOM, override this by setting the query parameter dom=shady when directing requests to the Rendertron service.

If you are using web components v1 and either webcomponents-lite.js or webcomponents-loader.js, set the query parameter wc-inject-shadydom=true when directing requests to the Rendertron service. This renderer service will force the necessary polyfills to be loaded and enabled.

Status codes

Status codes from the initial requested URL are preserved. If this is a 200, or 304, you can set the HTTP status returned by the rendering service by adding a meta tag.

<meta name="render:status_code" content="404" />

Installing & deploying

Building

To build rendertron-slim buf and protoc is required. Clone and install dependencies:

git clone https://github.com/nemoengineering/rendertron-slim.git
cd rendertron-slim
npm install
npm run build

Running locally

With a local instance of Chrome installed, you can start the server locally:

npm run start

Deploying using Docker

Rendertron no longer includes a Docker file. Instead, refer to Puppeteer documentation on how to deploy run headless Chrome in Docker.

Config

When deploying the service, set configuration variables by setting the following environment variables:

• PORT default 4000 - set the port to use for running and listening the rendertron service.
• HOST default 0.0.0.0 - set the hostname to use for running and listening the rendertron service.
• ALLOWED_RENDER_ORIGINS - restrict the endpoint to only service requests for certain domains. Specified as an array of strings. eg. "http://render.only.this.domain, http://or.this.domain". This is a strict prefix match, so ensure you specify the exact protocols that will be used (eg. http, https).
• CLOSE_BROWSER_AFTER_RENDERdefault false - true forces the browser to close and reopen between each page render, some sites might need this to prevent URLs past the first one rendered returning null responses.
• RESTRICTED_URL_PATTERNdefault null - set the restrictedUrlPattern to restrict the requests matching given regex pattern.