rendergun

A pre-render service for client-side rendered websites

Use Case

Some websites are client-side rendered with JavaScript. While this is great for building interactive websites, if not used correctly, it'll definitely hurt the Search Engine Optimization (SEO) and index ranking.

Most libraries provide a way to do Server-Side Rendering (SSR), which is perfect for SEO. But SSR is not always possible, so a Pre-rendering application such as Rendergun is another solution.

Rendergun uses a real browser to load your page, download all assets, execute the JavaScript, build the DOM and return the HTML as a string. This string can then be returned as a response to web crawlers such as Google, Bing, DuckDuckGo, etc.

Pre-rendering is recommended by Google. Visit https://developers.google.com/search/docs/guides/dynamic-rendering to learn more.

Features

• 🚀 Uses a real, stable and up-to-date Chromium (Google Chrome): Built on top of puppeteer, an API for Headless Chrome
• 👩🏻‍⚕️ Self-healing: Rendergun constantly checks the health of the browser instance and restart it if necessary.
• ⚡️ Cache: Pages are cached to provide lightning fast responses.
• 🔀 Skip unnecessary requests: Rendergun can skip requests that are not required for rendering, such as CSS and Images files, which can greatly increase the performance of the rendering process.
• 🐳 Runs on Docker: Rendergun has an official Docker image. Just pull and run it!

How to install

Rendergun can be used as a Node.js CLI or Docker container.

Rendergun Node.js CLI

# install rendergun install NPM 
$ npm i -g rendergun 
 
# start rendergun with default configuration 
$ rendergun

Rendergun Docker Container

docker run --name rendergun -p 3000:3000 goenning/rendergun

Operations

/render

• Use Case: Request an HTML rendered version of a webpage
• HTTP Method: GET or POST
• Parameters:

Location	Name	Default Value	Required	Comments
QueryString	url		Yes	which url to pre-render
Body	N/A		No	Rendergun will skip the initial page load of url and use the content of body to render the page. This is useful if the requestor knows what's the content of url as this can avoid an additional HTTP Request. When set, it should be of type text/html.
HTTP Header	x-rendergun-wait-until	load	No	which chrome event to wait before returning the HTML. Possible values are load, domcontentloaded, networkidle0,networkidle2
HTTP Header	x-rendergun-timeout	10000	No	timeout in milliseconds for Chrome to load the page
HTTP Header	x-rendergun-abort-request		No	a RegExp that aborts all requests that matches it. Useful to skip requests to CSS/Images files that are not required for pre-rendering
HTTP Header	x-rendergun-block-ads	false	No	true/false if Rendergun should skip requests to Ads/Trackers domains. This gives a small performance improvement and avoid unecessary tracking

Example: https://demo.fider.io is a client-side rendered page built with React. Look at the source and you'll see that only JavaScript files and a JSON object is returned by the server. The whole HTML is built by React when it's executed by the browser.

Start rendergun and open http://localhost:3000/render?url=https://demo.fider.io on your browser. The visual result should be the same, except that now the server has returned just the HTML content, without the JavaScript files and the JSON object. Web crawlers like Google, Bing and, DuckDuckGo prefer this over client-side rendered pages.

/-/health

• Use Case: Check if Rendergun is healthy
• HTTP Method: GET

This is used to verify if Rendergun and the Headless Chrome instance are healthy. If everything is OK, 200 status code is returned, otherwise 500. Rendergun will constantly monitor the health of Headless Chrome instance and restart it if necessary.

Customize

Rendergun can be customized by using Environment Variables. The following settings are available.

Name	Default Value	Comments
PORT	3000	which port Rendergun should bind to
CACHE_MAX_SIZE	100	how many megabytes should Rendergun use for caching
CACHE_MAX_AGE	1800	how long (in seconds) should items be cached