Ember FastBoot

An Ember CLI addon that allows you to render and serve Ember.js apps on the server. Using FastBoot, you can serve rendered HTML to browsers and other clients without requiring them to download JavaScript assets.

Currently, the set of Ember applications supported is extremely limited. As we fix more issues, we expect that set to grow rapidly. See Known Limitations below for a full-list.

The bottom line is that you should not (yet) expect to install this add-on in your production app and have FastBoot work.

Installation

From within your Ember CLI application, run the following command:

ember install ember-cli-fastboot

In order to get FastBoot working, you will first need to enable Ember Canary:

rm -rf bower_components
bower install --save ember#canary
bower install

Bower also prompts you to confirm various "resolutions" that it is unsure of. Make sure you pick ember#canary if prompted.

Running

• ember fastboot --serve-assets
• Visit your app at http://localhost:3000.

You may be shocked to learn that minified code runs faster in Node than non-minified code, so you will probably want to run the production environment build for anything "serious."

ember fastboot --environment production

You can also specify the port (default is 3000):

ember fastboot --port 8088

See ember help fastboot for more.

Known Limitations

While FastBoot is under active development, there are several major restrictions you should be aware of. Only the most brave should even consider deploying this to production.

Requires Ember Canary

We are actively improving Ember.js to ensure that it loads and renders correctly in environments without a DOM (notably Node.js in this case).

Because of that, FastBoot will require you to be running on a canary version of Ember for the foreseeable future.

To run your app with canary, run the following command:

bower install --save ember#canary

You will also need to ensure you have enabled HTMLbars. If you have not done so, see this blog post for steps on enabling HTMLbars in an Ember CLI application.

No didInsertElement

Since didInsertElement hooks are designed to let your component directly manipulate the DOM, and that doesn't make sense on the server where there is no DOM, we do not invoke either didInsertElement nor willInsertElement hooks.

No jQuery

Running most of jQuery requires a full DOM. Most of jQuery will just not be supported when running in FastBoot mode. One exception is network code for fetching models, which we intended to support, but doesn't work at present.

No JavaScript Served

Right now, this is only useful for creating an HTML representation of your app at a particular route and serving it statically. Eventually, we will support also serving the JavaScript payload, which can takeover once it has finished loading and making the app fully interactive.

In the meantime, this is probably only useful for cURL or search crawlers.

Troubleshooting

Because your app is now running in Node.js, not the browser, you'll need a new set of tools to diagnose problems when things go wrong. Here are some tips and tricks we use for debugging our own apps.

Verbose Logging

Enable verbose logging by running the FastBoot server with the following environment variables set:

DEBUG=ember-cli-fastboot:* ember fastboot

PRs adding or improving logging facilities are very welcome.

Developer Tools

You can get a debugging environment similar to the Chrome developer tools running with a FastBoot app, although it's not (yet) as easy as in the browser.

First, install the Node Inspector:

npm install node-inspector -g

Make sure you install a recent release; in our experience, older versions will segfault when used in conjunction with Contextify, which FastBoot uses for sandboxing.

Next, start the inspector server. We found the experience too slow to be usable until we discovered the --no-preload flag, which waits to fetch the source code for a given file until it's actually needed.

node-inspector --no-preload

Once the debug server is running, you'll want to start up the FastBoot server with Node in debug mode. One thing about debug mode: it makes everything much slower. Since the ember fastboot command does a full build when launched, this becomes agonizingly slow in debug mode.

Avoid the slowness by manually running the build in normal mode, then running FastBoot in debug mode without doing a build:

ember build && node --debug-brk ./node_modules/.bin/ember fastboot --no-build

This does a full rebuild and then starts the FastBoot server in debug mode. Note that the --debug-brk flag will cause your app to start paused to give you a chance to open the debugger.

Once you see the output debugger listening on port 5858, visit http://127.0.0.1:8080/debug?port=5858 in your browser. Once it loads, click the "Resume script execution" button (it has a ▶︎ icon) to let FastBoot continue loading.

Assuming your app loads without an exception, after a few seconds you will see a message that FastBoot is listening on port 3000. Once you see that, you can open a connection; any exceptions should be logged in the console, and you can use the tools you'd expect such as console.log, debugger statements, etc.