Designing Mobile Applications Like U.S. Big Tech: iOS and Android System Design

A hands-on mobile system design course on structurally designing iOS and Android apps

Mobile apps are not completed by simply creating great screens.
True mobile system design begins the moment the network goes down, the app is terminated, data is duplicated, and countless events arrive simultaneously.

This course is designed to help you develop the mobile architecture mindset expected at major U.S. tech companies by designing Instagram feeds, WhatsApp messaging, Uber location tracking, Netflix offline downloads, Spotify streaming, and ChatGPT- and Claude-style AI apps yourself.

You do not memorize a completed architecture from the beginning.
Starting with the simplest implementation, you directly discover and solve problems such as data inconsistencies, slow screens, duplicate messages, battery drain, app termination, and deployment failures.
Through this process, you gradually master the principles of offline-first design, sync engines, state machines, caching, retries, real-time connections, push notifications, observability, and AI-native architecture.

By comparing the platform constraints of iOS and Android, you will learn not only how to implement features but also how to design mobile systems that are fast, reliable, and capable of recovering from failures.

Recommended for those who:

After completing the course,

• You can structurally design large-scale mobile services, from requirements through failure response.

• You can design an offline-first architecture that can recover even after network disconnections and app termination.

• You can design real-time systems that include message ordering, reconnection, read receipts, and Push notifications.

• You can make iOS and Android architecture decisions that account for app lifecycle, battery, memory, and network constraints.

• You can design an AI-native mobile app architecture that combines LLM streaming UI with on-device and server-side AI.

• In interviews or at work, you can logically explain the reasons behind design decisions and their trade-offs rather than simply listing technology names.

Features of this course

1. A course where you encounter problems first, solve them, and learn the underlying principles along the way

This course does not explain a completed architecture from the beginning.
Instead, it starts with the simplest structure and has you directly confront the problems you will inevitably encounter in real-world services.

For example, with image loading,
we start by “simply fetching and displaying the image via its URL,”
and then directly encounter issues such as duplicate requests while scrolling, incorrect images being displayed, increasing memory usage, and cache invalidation.
Only then do you understand why concepts such as caching, request deduplication, cancellation, decoding, and disk caching are necessary.

In other words, this is not a course that merely introduces technology.
It is a course that helps you deeply understand why problems occur and how to solve them systematically.

2. A course that designs big tech case studies from a mobile perspective, end to end

We do not simply introduce the Instagram feed, WhatsApp messaging, Uber location tracking, Netflix offline downloads, Spotify streaming, or the ChatGPT and Claude mobile apps.

We design each case all the way through using the following flow.

• What requirements are there?

• What should the mobile client be responsible for?

• Where is the data stored?

• How does it work when offline?

• What should be restored when the app is terminated?

• How should real-time connections and push notifications divide their roles?

• How should performance, battery usage, security, and observability be designed?

Therefore, by the end of the course, you will move beyond simply thinking, “Oh, I guess an app like this would be built roughly this way,”
to the point where you can actually explain your design proposal.

You’ll learn the following.

Fundamental Principles of Mobile System Design and Data Architecture

In this section, you will learn the core mindset of mobile system design.
You will understand the difference between feature implementation and system design and define the scope of what the mobile client should actually be responsible for.

We will focus particularly on the following topics.

• Mobile System Design Approach

• State Management and Data Layer

• Single Source of Truth

• Caching and Cache Invalidation

• Offline-first

• Sync Engine

• Optimistic updates

• Conflict resolution

• App Lifecycle and Process Death Handling

• iOS and Android background execution models

Through this section
, you will move beyond the level of an “app that displays data received from the server”
and establish the principles for designing a recoverable, long-lasting mobile data architecture.

Real-time systems, performance optimization, Push, AI-native architecture

This section covers the most challenging problems in real-world services.

• WebSocket, SSE, and Polling Comparison

• Message ordering guarantees and read status handling

• Push Notification System Design

• Image Loading and Caching Pipeline

• Performance optimization for large-scale lists and feeds

• Memory, battery, and network budget design

• Mobile Observability Architecture

• Phased rollout and operations strategy

• On-device AI vs. Server AI

• LLM Streaming UI

• Agentic Mobile UX

Through this section,
rather than learning the concepts of each technology separately,
you will develop the ability to make integrated decisions about real-time features, performance, operations, and AI within a single app architecture.

The person who created this course

• Silicon Valley Survivor | American Snail 

  Drawing on experience and know-how gained at the forefront of the Global Tech Scene, this course shows non-majors how to overcome technical barriers and become the owners of their businesses.

  • Current) Founder of a Silicon Valley AI coding agent startup

    • Operating the self-developed AI tool 'Snailer CLI' (20K+ downloads)

    • Selected for the Google for Startups Program

  • Formerly an engineer at major U.S. tech companies and promising startups

    • Gave up the final stage at Amazon to start a company

    • Silicon Valley AI FinTech Startup Engineer

    • OpenAI / Meta / Apple / Adobe / Amazon Full-Stack Fellowship

    • Domestic search engine portal, fintech development

    • AI startup AR/B2B/SDK development

  • Proven teaching expertise

    • Double major in Computer Science and Business Administration at a four-year university in Seoul, with extensive startup experience

    • Produced over 2,100 students in total; 4.6K+ followers on SNS Threads and 500+ Substack followers.

    • Threads: https://www.threads.com/@rich_l_2024?igshid=NTc4MTIwNjQ2YQ==

    • Substack: https://open.substack.com/pub/1234373801

I never viewed mobile app development as simply “creating screens.”
In practice, when you build an app, the problems begin after the screens are finished.

Images load slowly, networks disconnect, apps terminate, real-time connections become unstable, caches get tangled, and users feel that “the app is acting strangely” for no apparent reason.
What you need at that moment is not another new library, but a perspective that sees the system as a whole.

I have consistently worked on architecture, performance, real-time processing, streaming, data flow, and server integration issues in real-world service environments, with a focus on iOS development.
Through my experience with search portals, fintech services, vision/AR-based apps, real-time audio, video features, and mobile-server integration architectures, I came to one common realization.

Many developers learn how to “implement features,” but
it is difficult to systematically learn “why structures break down” and “how to design them.”

This course was created specifically to bridge that gap.

Instead of listing theories,
the course is designed to start with the simplest implementation, reveal problems, and teach the underlying principles as you solve them.
That is why the goal of this course is not to introduce a wide range of technologies, but to
enable students to determine the right design direction on their own when they encounter a new mobile service.

Do you have any questions?

Notes Before Taking the Course