Single page apps deliver fantastically rich user experiences, and they open up an entirely different avenue for continuous deployment. Separating out a front-end application from the server is a sound strategy for breaking up the responsibilities of the team. Maintaining a separate front-end code base allows teams to iterate on features quickly and interact through formalized contracts in the form of an API.
Not everything about delivering static assets is so rosy though. There are hosting and delivery pitfalls that your team should be aware of before embarking on continuously deploying static assets. Here are some tips for effectively deploying statically hosted applications iteratively, safely, and most importantly, efficiently.
1. Package and Deploy Using State of the Art Tools
If your team has decided to deploy client and server code independently, there's a good chance that the server isn't written in Node. That doesn't stop you from using Node and NPM to build and package your application! You're free to use state of the art tools for packaging and development, regardless of your server-side framework.
Once your build and testing process is independent of a server framework, it frees up the delivery process as well. After the front-end application passes integration testing, the CI server can build a production release (see tip number two) and deliver it directly for distribution (see tip number five).
2. Minification, Compression, and Source Maps Are Not Optional
Deploying a single page app means more than uploading concatenated code to a server. It deserves all the byte-saving care and attention you would give to the assets served up by a production-grade web framework. That means it should be minified, compressed, and most certainly includes source maps.
3. Optimize Code and Style Delivery
This may be slightly controversial given the recent trend toward declaring styles along side view components, but there's a trade off to bundling styles along with code.
Typically a browser can download the CSS and JS files in parallel, lowering the time until first paint after load. That performance boost isn't possible when all of the assets are bundled together. Instead, all of the styles and code are smashed together in a single large file, and clients end up staring at a blank screen while they wait for assets to download.
It complicates the delivery process slightly to have multiple files, but the size and performance benefits are worth the trouble.
4. Deliver Separate Bundles
Unless you are an ultra purist, every packaged application is composed of both library modules and application code. Chances are that your application code changes much more frequently than library modules. When you serve up a giant concatenated bundle, the client is forced to download everything fresh with every minor change, no matter how small it is. Application bundles routinely push a 3MB payload, which is a lot of code to download again just because a few lines of application code changed.
To avoid this issue, you should separate your application into at least two bundles: one for concatenated library code and another for application code. In the bright future of HTTP/2 connection parallelism, individual files may be served up in parallel, and this sort of planning won't be necessary. For right now, a bit of asset bundle splitting will speed up the experience for your users on every release.
5. Get Friendly With a Content Distribution Network
Serve static applications from a content distribution network. This allows clients to keep pointing at the same URL while maintaining caching semantics. It also allows you to perform invalidations when you release code, despite the lack of asset fingerprinting. An invalidation updates the cached version of the application that's held at each edge server, the servers that actually serve the application to clients.
Be warned, invalidations can be slow, taking 10 minutes or more on Amazon CloudFront. This unpredictable asynchronous behavior is part of why extra care has to be taken around versioning and releases.
6. Continuity Knows No Version
Don't rely on users reloading their browser. Assume that some users will be running older versions of the app, and be prepared to handle requests from deprecated features. Consider releases as a continuum of changes and decide how long your release cycle is.
At a certain point it isn't practical to support every old release and the bugs they may have contained. Unless you are deploying to a kiosk with an especially infrequent update cycle, you can safely assume users will reload once a week.
7. Roll Features Out Gradually
Use feature flags to roll features out gradually. Ember is a stellar example of shipping code with features available, but it's disabled by default. The code is live and in production, but most people aren't using it. Once it has been vetted in the wild, with staff or with a fraction of your users, you can release a new version with the feature enabled.
The same approach is often used when releasing server side code, but the stakes are higher with statically hosted single page apps. A gradual approach is crucial because rolling code back can only be as fast as your CDN's invalidation period. That means you could have a botched release in production for 10 minutes or more without being able to revoke it.
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