Client Technologies
iOS
Apple's mobile operating system for iPhones and iPads.
Android
Google's mobile operating system for a wide range of devices.
Web
Accessed through a web browser on a desktop or mobile device.
Choosing the Right Clients in an Interview
When you're in a system design interview, clarifying the clients is a critical first step. For most product-facing applications, stating that you'll support iOS, Android, and Web is a standard and sufficient answer. This covers the vast majority of users.
However, some systems have more complex client needs. For example:
- Internal Tools: If you're designing a system for a company's internal use (e.g., a customer support dashboard), the primary client might be a web-based admin panel.
- Multiple User Roles: For applications like Uber, there are distinct clients for different user groups: a Rider App (iOS, Android) and a Driver App (iOS, Android). Each has unique features and requirements.
Always make sure to ask clarifying questions to determine if different client types are needed. This demonstrates a thorough understanding of the problem and an ability to design for specific use cases.
Deep Dive: Supporting Different Clients
Mobile Apps (iOS and Android)
Why: Mobile apps provide the best user experience and performance, with full access to device features like the camera, GPS, and push notifications.
How it works:
- Native: We build separate applications for each platform using their native programming languages and SDKs (Swift/Objective-C for iOS, Kotlin/Java for Android). This allows us to create a user interface that is tailored to each platform's design guidelines.
- Cross-Platform: We use a framework like React Native or Flutter to build our application. These frameworks provide a set of tools and libraries that allow us to write code in a single language (JavaScript for React Native, Dart for Flutter) and then compile it to native code for each platform.
Trade-offs:
- Pros: Best performance (native), faster development (cross-platform), seamless user experience, full access to device features.
- Cons: More expensive and time-consuming to develop and maintain (native), performance may not be as good as a native app (cross-platform).
Web Apps
Why: Web applications are accessible from any device with a web browser, making them a versatile choice for reaching a broad audience. They don't require installation from an app store, which can be a significant advantage.
How it works: Web apps are built using standard web technologies like HTML, CSS, and JavaScript. They are typically developed using a front-end framework like React (with Next.js) for building modern, server-rendered applications, or a full-stack framework like Ruby on Rails for rapid development.
Trade-offs:
- Pros: Accessible from any device, no app store approval, easy to update.
- Cons: Limited access to device features, performance can be a concern, and the user experience may not be as seamless as a native app.
Internal Services as Clients
Why: In a microservices architecture, services often act as clients to other services. These are not user-facing clients, but rather internal services that consume APIs from other internal services. For example, a distributed job scheduler might be a client to a service that sends email notifications.
How it works: Internal service clients typically communicate with other services via APIs, such as REST or gRPC. They are not graphical user interfaces, but rather programmatic interfaces that allow services to interact with each other.
Trade-offs:
- Pros: Enables a decoupled, microservices-based architecture, allows for services to be developed and deployed independently.
- Cons: Adds complexity to the system, requires careful management of APIs and service discovery.
Supporting Different OS and Clients
When building for multiple clients, it's crucial to consider the differences in operating systems and screen sizes.
- Responsive Design: Your web application should adapt to different screen sizes and orientations, providing a good user experience on both desktop and mobile devices. This can be achieved using CSS media queries and flexible layouts.
- Media Files: To ensure a good user experience on all devices, you should provide different resolution media files for different screen sizes. For example, you can use high-resolution images for desktop and lower-resolution images for mobile devices to reduce loading times.
- Operating System Specific Features: If you are building a native or cross-platform application, you should consider using OS-specific features to provide a better user experience. For example, you can use push notifications on both iOS and Android, but the implementation details will be different for each platform.