Interview study guide
APIs & devices, end to end.
The layer between a web UI and real hardware: APIs devices and partners depend on, Telnet and SSH control, admin UIs that survive reboots, and the Android platform underneath. Every server and client example runs on Node and prints what the page says.
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01Devices, Platforms and This RoleWhat device platform engineering is, the parts of a managed device, what Poly's public documentation says about its video systems and PolyOS, how one admin click travels from the web UI to the operating system, how an OS migration like 4.x → 5.x is run, and how to talk about all of it in the interview.02REST API Design for DevicesHow to shape an HTTP API that admins, the on-device web UI, cloud management and partners all drive: resources for settings, status and operations, safe methods and retries, JSON Merge Patch, long-running reboots and updates, ETags so two admins don't overwrite each other, RFC 9457 errors, atomic bulk configuration, and what a small device can afford — with one simulated device API, built in Express 5, that grows through the chapter.03Documenting APIs with OpenAPIOne machine-readable contract for a device API: what OpenAPI 3.1 is, a real spec for a room device, enforcing it on every request and response, generating types and docs from it, design-first vs code-first, and catching breaking changes before a fleet of devices does.04Versioning and CompatibilityChanging a device API without breaking a fleet on old firmware: why devices make versioning hard, where the version goes, the rules for compatible change, capability discovery, deprecation and sunset headers, and testing every client against every firmware.05Security for Device APIsWho may talk to the device and how it proves who they are: admin sessions and integration tokens with scopes, TLS when the device has no public name, a web UI served from an IP address, hardening against default passwords and guessing, least privilege with an audit trail, and signed updates.06Telnet, SSH and Command-Line ControlLine-based control channels for devices: what Telnet really is on the wire, a command server in Node that survives partial packets, a grammar machines can parse, notifications on the same socket, SSH with ssh2, one command layer behind REST, Telnet and SSH, and how to test and lock it all down.07Real-Time Device StateGetting live status from a device to the web UI, touch controllers and integrations: choosing a transport, designing events with sequence numbers, snapshot plus events, reconnecting across reboots, and serving many clients from a small box.08Admin Web UIs for HardwareThe web UI an administrator uses to run a device: what it must do well, forms and validation generated from one settings schema, apply and restart flows that can't lock you out, software updates with honest progress and rollback, behaviour while the device is rebooting or unreachable, configuration import and provisioning, and accessibility and localisation.09Integrating with Android and the PlatformThe Android side of a device's web UI and APIs: where the server process lives and how it stays alive, the Android 11→12→13 behaviour changes that hit such apps, Binder/AIDL and permissions for talking to platform services, contracts between the SDK, platform and web teams, and debugging one request from the browser down to a system service.10SDKs and Developer-Facing InterfacesWhat turns a device API into something partners enjoy using: a small SDK in modern JavaScript with typed methods, sessions, timeouts, safe retries, a real error model and paging, then how to version, deprecate, release and document it so integrations survive years of firmware.11Testing and Delivering Device SoftwareHow software for a fleet of devices gets proved and shipped: API tests at three levels, simulators and emulators, real hardware in a lab, a pipeline that signs what it builds, staged rollouts that stop themselves, and the flags, telemetry and diagnostics you need once it's in the field.12Video Conferencing BasicsWhat happens in a video call, from the first SIP or WebRTC message to the packets on the wire: signalling and media, SDP, ICE, STUN and TURN, room systems and their provider modes, and the statistics a device exposes when a call goes wrong.13Review QuestionsRapid revision before the interview: questions an interviewer for a device-platform full stack role might ask, with answers you can say out loud in a minute, each linked to the topic that explains it in depth.
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