Simply put, performance matters. We know members want to immediately start browsing or watching their favorite content and have found that faster startup leads to more satisfying usage. So, when building the long-awaited update to netflix.com, the Website UI Engineering team made startup performance a first tier priority.
The impact of this effort netted a 70% reduction in startup time, and was focused in three key areas:
- Server and Client Rendering
Server and Client Rendering
This separation led to undesirable results in our startup time. Every time a visitor came to any page on netflix.com our Java tier would generate the majority of the response needed for the entire page's lifetime and deliver it as HTML markup. Often, users would be waiting for the generation of markup for large parts of the page they would never visit.
We find the flexibility afforded by server and client rendering allows us to make intelligent choices of what to request and render in the server and the client, leading to a faster startup and a smoother transition between views.
In order to support identical rendering on the client and server, we needed to rethink our rendering pipeline. Our previous architecture's separation between the generation of markup on the server and the enhancement of it on the client had to be dropped.
Three large pain points shaped our new Node.js architecture:
- Context switching between languages was not ideal.
- Enhancement of markup required too much direct coupling between server-only code generating markup and the client-only code enhancing it.
- We’d rather generate all our markup using the same API.
Node.js and React.js are natural fits for this style of application. With Node.js and React.js, we can render from the server and subsequently render changes entirely on the client after the initial markup and React.js components have been transmitted to the browser. This flexibility allows for the application to render the exact same output independent of the location of the rendering. The hard separation is no longer present and it's far less likely for the server and client to be different than one another.
Without shared rendering logic we couldn't have realized the potential of rendering only what was necessary on startup and everything else as data became available.
Time To Interactive
In order to test and understand the impact of our choices, we monitor a metric we call time to interactive (tti).
Amount of time spent between first known startup of the application platform and when the UI is interactive regardless of view. Note that this does not require that the UI is done loading, but is the first point at which the customer can interact with the UI using an input device.
For applications running inside a web browser, this data is easily retrievable from the Navigation Timing API (where supported).
Work is Ongoing
We firmly believe high performance is not an optional engineering goal – it's a requirement for creating great user-experiences. We have made significant strides in startup performance, and are committed to challenging our industry’s best-practices in the pursuit of a better experience for our members.
Over the coming months we'll be investigating Service Workers, ASM.js, Web Assembly, and other emerging web standards to see if we can leverage them for a more performant website experience. If you’re interested in helping create and shape the next generation of performant web user-experiences apply here.