Rendertron is a dockerized, headless Chrome rendering solution designed to render & serialise web pages on the fly.
Rendertron is designed to enable your Progressive Web App (PWA) to serve the correct content to any bot that doesn't render or execute JavaScript. Rendertron runs as a standalone HTTP server. Rendertron renders requested pages using Headless Chrome, auto-detecting when your PWA has completed loading and serializes the response back to the original request. To use Rendertron, your application configures middleware to determine whether to proxy a request to Rendertron. Rendertron is compatible with all client side technologies, including web components.
Demo endpoint
A demo Rendertron service is available at https://render-tron.appspot.com/. It is not designed to be used as a production endpoint. You can use it, but there are no uptime guarantees.
Once you have the service up and running, you'll need to implement the differential serving layer. This checks the user agent to determine whether prerendering is required.
This is a list of middleware available to use with the Rendertron service:
- Express.js middleware
- Firebase functions (Community maintained)
- ASP.net core middleware (Community maintained)
Rendertron is also compatible with prerender.io middleware. Note: the user agent lists differ there.
GET /render/<url>
The render endpoint will render your page and serialize your page.
GET /screenshot/<url>
POST /screenshot/<url>
The screenshot endpoint can be used to verify that your page is rendering
correctly.
Both endpoints support the following query parameters:
widthdefaults to1000- specifies viewport width.heightdefaults to1000- specifies viewport height.
Additional options are available as a JSON string in the POST body. See
Puppeteer documentation
for available options. You cannot specify the type (defaults to jpeg) and
encoding (defaults to binary) parameters.
When setting query parameters as part of your URL, ensure they are encoded correctly. In JS,
this would be encodeURIComponent(myURLWithParams). For example to specify page=home:
https://render-tron.appspot.com/render/http://my.domain/%3Fpage%3Dhome
The service detects 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.
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.
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 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" />To install Rendertron and run it locally, first install Rendertron:
npm install -g rendertronWith Chrome installed on your machine run the Rendertron CLI:
rendertronThis project requires Node 7+ and Docker (installation instructions). For deployment this project uses the Google Cloud Platform SDK.
Clone and install dependencies:
git clone https://github.com/GoogleChrome/rendertron.git
cd rendertron
npm installWith a local instance of Chrome installed, you can start the server locally:
npm run startAfter installing docker, build and run the docker image
docker build -t rendertron . --no-cache=true
docker run -it -p 8080:8080 --name rendertron-container rendertronLoad the homepage in any browser:
http://localhost:8080/Stop the container:
docker kill rendertron-containerClear containers:
docker rm -f $(docker ps -a -q)In the case where your kernel lacks user namespace support or are receiving a ECONNREFUSED error when trying to access the service in the container (as noted in issues 2 and 3), the two recommended methods below should solve this:
- [Recommended] - Use Jessie Frazelle' seccomp profile and
-security-optflag - Utilize the
--cap-add SYS_ADMINflag
[Recommended] Start a container with the built image using Jessie Frazelle' seccomp profile for Chrome:
wget https://raw.githubusercontent.com/jfrazelle/dotfiles/master/etc/docker/seccomp/chrome.json -O ~/chrome.json
docker run -it -p 8080:8080 --security-opt seccomp=$HOME/chrome.json --name rendertron-container rendertronStart a container with the built image using SYS_ADMIN:
docker run -it -p 8080:8080 --cap-add SYS_ADMIN --name rendertron-container rendertronTo check if your kernel is compatible with Docker, follow Docker's instructions. For CentOS 7, which doesn't have user namespaces enabled, you will need to enable them.
By default the size of /dev/shm in Docker is 64mb, which may result in Chrome crashes. To increase the size of /dev/shm you can specify the size to Docker when running the image.
docker run ... --shm-size=256m
In the future, it will be possible to using /tmp instead of /dev/shm. See the Chromium bug for more detail.
gcloud app deploy app.yaml --project <your-project-id>
When deploying the service, set configuration variables by including a config.json in the
root. Available configuration options:
cachedefaultfalse- set totrueto enable caching on Google Cloud using datastore