Render Models at LinkedIn
November 22, 2022
Co-Authors: Mahesh Vishwanath, Eric Babyak, Sonali Bhadra, Umair Saeed
We use render models for passing data to our client applications to describe the content (text, images, buttons etc.) and the layout to display on the screen. This means most of such logic is moved out of the clients and centralized on the server. This enables us to deliver new features faster to our members and customers while keeping the experience consistent and being responsive to change.
Traditionally, many of our API models tend to be centered around the raw data that’s needed for clients to render a view, which we refer to as data modeling. With this approach, clients own the business logic that transforms the data into a view model to display. Often this business logic layer can grow quite complex over time as more features and use cases need to be supported.
This is where render models come into the picture. A render model is an API modeling strategy where the server returns data that describes the view that will be rendered. Other commonly used terms that describe the same technique are Server Driven User Interface (SDUI), or View Models. With render models, the client business logic tends to be much thinner, because the logic that transforms raw data into view models now resides in the API layer. For any given render model, the client should have a single, shared function that is responsible for generating the UI representation of the render model.
Architectural comparison between data modeling and render modeling
To highlight the core differences in modeling strategy between a render model and data model, let’s walk through a quick example of how we can model the same UI with these two strategies. In the following UI, we want to show a list of entities that contain some companies, groups, and profiles.
An example UI of an ‘interests’ card to display to members
Following the data model approach, we would look at the list as a mix of different entity types (members, companies, groups, etc.) and design a model so that each entity type would contain the necessary information for clients to be able to transform the data into the view shown in the design.
When applying a render model approach, rather than worry about the different entity types we want to support for this feature, we look at the different UI elements that are needed in the designs.
An ‘interests’ card categorized by UI elements
In this case, we have one image, one title text, and two other smaller subtexts. A render model represents these fields directly.
With the above modeling, the client layer remains very thin as it simply displays each image/text returned from the API. The clients are unaware of which underlying entity each element represents, as the server is responsible for transforming the data into displayable content.
API design with render models
API modeling with render models can live on a spectrum between the two extremes of frontend modeling strategies, such as pure data models and pure view models. With pure data models, different types of content use different models, even if they look the same on UI. Clients know exactly what entity they are displaying and most of the business logic is on clients, so complex product UX can be implemented as needed. Pure view models are heavily-templated and clients have no context on what they are actually displaying with almost all business logic on the API. In practice, we have moved away from using pure view models due to difficulties in supporting complex functionality, such as client animations and client-side consistency support, due to the lack of context on the clients’ end.
Typically, when we use render models, our models have both view model and data model aspects. We prefer to use view modeling most of the time to abstract away most of the view logic on the API and to keep the view layer on the client as thin as possible. We can mix in data models as needed, to support the cases where we need specific context about the data being displayed.
A spectrum of modeling strategies between pure view models and pure data models
To see this concretely, let’s continue our previous example of a FollowableEntity. The member can tap on an entity to begin following the profile, company, or group. As a slightly contrived example, imagine that we perform different client side actions based on the type of the entity. In such a scenario, the clients need to know the type of the entity and at first brush it might appear that the render models approach isn’t feasible. However, we can combine theseapproaches to get the best of both worlds. We can continue to use a render model to display all the client data but embed the data model inside the render model to provide context for making the follow request.
Client theming, layout, and accessibility
Clients have the most context about how information will be displayed to users. Understanding the dynamics of client-side control over the UX is an important consideration when we build render models. This is particularly important because clients can alter display settings like theme, layout, screen size, and dynamic font size without requesting new render models from the server.
Properties like colors, local image references, borders, or corner radius are sent using semantic tokens (e.g., color-action instead of blue) from our render models. Our clients maintain a mapping from these semantic tokens to concrete values based on the design language for the specific feature on a given platform (e.g. iOS, Android, etc.). Referencing theme properties with semantic tokens enables our client applications to maintain dynamic control over the theme.
For the layout, our render models are not intended to dictate the exact layout of the UI because they are not aware of the total available screen space. Instead, the models describe the order, context, and priorities for views, allowing client utilities to ultimately determine how the components should be placed based on available space (screen size and orientation). One way we accomplish this is by referring to the sizes of views by terms like “small” or “large” and allowing clients to apply what that sizing means based on the context and screen size.
It is critical that we maintain the same level of accessibility when our UIs are driven by render models. To do so, we provide accessibility text where necessary in our models, map our render models to components that have accessibility concerns baked in (minimum tap targets), and use semantics instead of specific values when describing sizes, layouts, etc.
Write use cases
One of the most challenging aspects of render models is dealing with write use cases, like filling forms and taking actions on the app (such as following a company, connecting with a person, sending a message, etc.). These use cases need specific data to be written to backends and cannot be modeled in a completely generic way, making it hard to use render models.
Actions are modeled by sending the current state of the action and its other possible states from the server to the clients. This tells the clients exactly what to display. In addition, it allows them to maintain any custom logic to implement a complex UI or perform state-changing follow-up actions.
To support forms, we created a standardized library to read and write forms, with full client infrastructure support out of the box. Similar to how traditional read-based render models attempt to leverage generic fields and models to represent different forms of data, our standardized forms library leverages form components as its backbone to generically represent data in a form by the type of UI element it represents (such as a ‘single line component’ or a ‘toggle component’).
Render models in practice
As we have mentioned above, the consistency of your UI is an important factor when leveraging render models. LinkedIn is built on a semantics-based design system that includes foundations like color and text, as well as shared components such as buttons and labels. Similarly, we have created layers of common UX render models in our API that include foundational and component models, which are built on top of those foundations.
Our foundational models include rich representations of text and images and are backed by client infrastructure that renders these models consistently across LinkedIn. Representing rich text through a common model and render utilities enables us to provide a consistent member experience and maintain our accessibility standards (for instance, we can restrict the usage of underlining in text that is not a link). Our image model and processing ensures that we use the correct placeholders and failure images based on what the actual image being fetched presents (e.g., a member profile). These capabilities of the foundational models are available without any client consumer knowledge of what the actual text or image represents and this information is all encapsulated by the server-driven model and shared client render utilities.
The foundational models can be used on their own or through component models that are built on top of the foundations. They foster re-use and improve our development velocity by providing a common model and shared infrastructure that resolves the component. One example is our common insight model, which combines an image with some insightful text.
A commonly used ‘insight’ model used throughout the site
Over the years, many teams at LinkedIn have taken on large initiatives to re-architect their pages based on render model concepts built on top of these foundational models. No two use cases are exactly alike, but a few of the major use cases include:
The profile page, which is built using a set of render model-based components stitched together to compose the page. For more details on this architecture, see this blog post published earlier this year.
The search results page, built using multiple card render model templates to display different types of search results in a consistent manner. See this blog post for more details.
The main feed, built centered around the consistent rendering of one update with optional components to allow for variability based on different content types.
A feed component designed around a several components
- The notifications tab, which helped standardize 50+ notification types into one simple render model template.
A notifications card designed using a standardized UI template
All of these use cases have seen some of the key benefits highlighted in this post: simpler client-side logic, a consistent design feel, faster iteration, and development and experimentation velocity for new features and bugs.
Render model tradeoffs
Render models come with their pros and cons, so it is important to properly understand your product use case and vision before implementing them.
With render models, teams are able to create leverage and control when a consistent visual experience, within a defined design boundary, is required across diverse use cases. This is enabled by centralizing logic on the server rather than duplicating logic across clients. It fosters generalized and simpler client-side implementation, with clients requiring less logic to render the user interface since most business logic lives on the server.
Render models also decrease repeated design decisions and client-side work to onboard use cases when the use case fits an existing visual experience. It fosters generalized API schemas, thereby encouraging reuse across different features if the UI is similar to an existing feature.
With more logic pushed to the API and a thin client-side layer, it enables faster experimentation and iteration as changes can be made by only modifying the server code without needing client-side changes on all platforms (iOS, Android, and Web). This is especially advantageous with mobile clients that might have older, but still supported versions in the wild for long periods of time.
Similarly, as most of the business logic is on the server, it is likely that any bugs will be on the server instead of clients. Render models enable faster turnaround time to get these issues fixed and into production, as server-side fixes apply to all clients without needing to wait for a new mobile app release and for users to upgrade.
As mentioned previously, render models rely on consistent UIs. However, if the same data backs multiple, visually-distinct UIs, it reduces the reusability of your API because the render model needs more complexity to be able to handle the various types of UIs. If the UI does need to change outside the framework, the client-code and server code needs to be updated, sometimes in invasive ways. By comparison, UI-only changes typically do not require changes to data models. For some of these reasons, upfront costs to implement and design render models are often higher due to the need to define the platform and its boundaries, especially on the client.
Render models are un-opinionated about writes and occasionally require write-only models or additional work to write data. This is contrasted with data models where the same data models can be used in a CRUD format.
Client-side tracking with render models has to be conceived at the design phase, where tracking with data models is more composable from the client. It can be difficult to support use case-specific custom tracking in a generic render model.
Finally, there are some cases where client business logic is unavoidable such as in cases with complex interactions between various user interface elements. These could be animations or client-data interactions. In such scenarios, render models are likely not the best approach as, without the specific context, it becomes difficult to have any client-side business logic.
When to use render models?
Render models are most beneficial when building a platform that requires onboarding many use cases that have a similar UI layout. This is particularly useful when you have multiple types of backend data entities that will all render similarly on clients. Product and design teams must have stable, consistent requirements and they, along with engineering, need to have a common understanding of what kinds of flexibility they will need to support and how to do so.
Additionally, if there are complex product requirements that need involved client-side logic, this may be a good opportunity to push some of the logic to the API. For example, it is often easier to send a computed text from the API directly rather than sending multiple fields that the client then needs to handle in order to construct the text. Being able to consolidate/centralize logic on the server, and thus simplifying clients, makes their behavior more consistent and bug-free.
On the flip side, if there is a lack of stability or consistency in products and designs, any large product or design changes are more difficult to implement with render models due to needing schema changes.
Render models are effective when defining generic templates that clients can render. If the product experience does not need to display different variants of data with the same UI, it would be nearly impossible to define such a generic template, and would often be simpler to use models that are more use case-specific rather than over-generalizing the model designs.
Render models have been adapted through many projects and our best practices have evolved over several years. Many have contributed to the design and implementation behind this modeling approach and we want to give a special shoutout to Nathan Hibner, Zach Moore, Logan Carmody, and Gabriel Csapo for being key drivers in formulating these guidelines and principles formally for the larger LinkedIn community.