Hermes Wiki

9. Front-End Web and Mobile

These services support the development, deployment, and testing of modern web and mobile applications.

Service Introduction: A comprehensive suite of tools (CLI, Libraries, UI, Hosting) for building and deploying full-stack web and mobile apps.

Common Usage: Accelerating the creation of app backends (auth, storage, data) and managing CI/CD for front-end assets.

Project Examples:

Building a React web app with a managed Cognito-backed authentication system.
Deploying a globally available static website with automated SSL and branch previews.

Service Introduction: A fully managed service for creating, publishing, maintaining, and securing APIs at any scale.

Common Usage: Acting as the "front door" for applications to access backend logic in Lambda, ECS, or on-premises.

API Types (exam-critical):

REST API — Full feature set: request/response transformation, API keys + usage plans, per-stage caching, WAF integration, private VPC endpoints. Higher cost and latency than HTTP APIs. Use when a question needs advanced request validation, transformation, or caching.
HTTP API — A lighter-weight, lower-latency, lower-cost alternative to REST APIs for simple proxy integrations (commonly Lambda). Lacks REST API's advanced features (no built-in caching, fewer authorization options). Correct answer when a question emphasizes "lowest cost" or "lowest latency" for a simple API, with no advanced transformation/caching requirement.
WebSocket API — For persistent, two-way, real-time communication (chat apps, live dashboards, multiplayer games) where the server needs to push data to connected clients without the client re-polling. The tell: "real-time bidirectional communication" or "server pushes updates to the client."

Throttling & Caching (exam-critical):

Throttling — API Gateway enforces account/API-level and per-usage-plan rate limits (steady-state requests/sec + burst) to protect backend services from being overwhelmed; requests beyond the limit get an HTTP 429. Combine with API Keys + Usage Plans to give different customers/tiers different rate limits (e.g., free tier vs. paid tier).
API Gateway Caching — Caches backend responses at the stage level for a configurable TTL, reducing the number of calls that actually reach Lambda/backend — the standard answer for "reduce backend load and improve response times for frequently-requested, rarely-changing data" (REST APIs only, not HTTP APIs).

Project Examples:

Exposing a serverless RESTful API to a mobile application.
Implementing throttling and API key management for a public SaaS product with free and paid usage tiers.
Building a low-cost, low-latency HTTP API in front of a single Lambda function for a simple internal microservice.
Powering a live multiplayer game's real-time state updates using a WebSocket API.

Service Introduction: An application testing service that lets you test web and mobile apps against real browsers and 2,500+ physical devices.

Common Usage: Improving application quality by automating cross-device UI testing and performance profiling.

Project Examples:

Running automated Selenium tests across various versions of Chrome and Firefox.
Testing a mobile app's performance on dozens of different Android and iOS device models.