283 lines
8.0 KiB
Markdown
283 lines
8.0 KiB
Markdown
# OTA Reference Design
|
||
|
||
> A practical guide to designing reliable, secure, and maintainable over-the-air (OTA) update systems for embedded Linux devices.
|
||
|
||
---
|
||
|
||
## About This Repository
|
||
|
||
This repository presents a practical reference design for building over-the-air (OTA) update systems for embedded Linux devices.
|
||
|
||
Rather than documenting a particular framework or vendor-specific solution, it focuses on the engineering principles that make OTA systems reliable, secure, and maintainable.
|
||
|
||
The goal is to explain **why** modern OTA systems are designed the way they are, what problems they solve, and what trade-offs different approaches involve.
|
||
|
||
Although many examples use Raspberry Pi as a demonstration platform, the concepts are applicable to a wide range of embedded Linux systems.
|
||
|
||
---
|
||
|
||
## Why This Repository Exists
|
||
|
||
There is no shortage of documentation for OTA frameworks.
|
||
|
||
You can easily find documentation for tools such as:
|
||
|
||
- Mender
|
||
- RAUC
|
||
- SWUpdate
|
||
- OSTree
|
||
- A/B Updates
|
||
|
||
However, these resources usually explain **how to use a particular tool**, not **why OTA systems are designed this way**.
|
||
|
||
Questions like these are often left unanswered:
|
||
|
||
- Why do many devices use A/B partitions?
|
||
- Why are bootloaders involved in the update process?
|
||
- Why is rollback necessary?
|
||
- What happens if power is lost during an update?
|
||
- Why are update images signed?
|
||
- Why are atomic updates important?
|
||
- How do production devices remain recoverable after failures?
|
||
|
||
This repository attempts to answer those engineering questions.
|
||
|
||
---
|
||
|
||
## What You'll Learn
|
||
|
||
Throughout this series we will explore topics including:
|
||
|
||
- OTA architecture
|
||
- Boot process
|
||
- Update strategies
|
||
- Full-image vs package updates
|
||
- A/B partition layouts
|
||
- Bootloader interaction
|
||
- Rollback mechanisms
|
||
- Atomic updates
|
||
- Image verification
|
||
- Digital signatures
|
||
- Secure Boot
|
||
- Failure recovery
|
||
- Delta updates
|
||
- Version management
|
||
- Testing strategies
|
||
- Production deployment considerations
|
||
|
||
The emphasis is always on understanding the underlying design rather than memorizing a particular implementation.
|
||
|
||
---
|
||
|
||
## Repository Structure
|
||
|
||
The structure below includes the current documentation, PlantUML diagrams, and A/B simulation. Hardware demonstrations and later chapters will be added as the practical material develops.
|
||
|
||
```text
|
||
ota-reference-design/
|
||
│
|
||
├── docs/
|
||
│ ├── 00-series-overview.md
|
||
│ ├── 01-what-is-an-ota-update.md
|
||
│ ├── 02-update_strategies.md
|
||
│ ├── 03-system-architecture.md
|
||
│ ├── 04-starting-an-updated-system-or-service.md
|
||
│ ├── 05-storage-layout.md
|
||
│ ├── 06-atomic-updates.md
|
||
│ ├── ...
|
||
│
|
||
├── diagrams/
|
||
│ ├── plantuml/
|
||
│ └── rendered/
|
||
│
|
||
├── examples/
|
||
│ └── simulations/
|
||
│ ├── ab-trial-boot/
|
||
│ └── interrupted-installation/
|
||
│
|
||
├── adr/
|
||
│ ├── ADR-001-repository-name.md
|
||
│ ├── ADR-002-license.md
|
||
│ └── ADR-003-reference-design.md
|
||
│
|
||
└── readme.md
|
||
```
|
||
|
||
---
|
||
|
||
## Learning Path
|
||
|
||
The chapters are designed to build on each other. The current chapters are:
|
||
|
||
- [01. What Is an OTA Update?](01-what-is-an-ota-update.md)
|
||
- [02. Choosing an OTA Update Strategy](02-update_strategies.md)
|
||
- [03. OTA System Architecture](03-system-architecture.md)
|
||
- [04. Starting an Updated System or Service](04-starting-an-updated-system-or-service.md)
|
||
- [05. Storage Layout](05-storage-layout.md)
|
||
- [06. Atomic Updates](06-atomic-updates.md)
|
||
|
||
To catch up on additions and revisions, see the [changelog](../CHANGELOG.md), with dated summaries and links to chapters, diagrams, simulations, and related history.
|
||
|
||
The learning path below also includes planned chapters.
|
||
|
||
```text
|
||
Introduction
|
||
│
|
||
▼
|
||
Update Strategies
|
||
│
|
||
▼
|
||
System Architecture
|
||
│
|
||
▼
|
||
System and Service Startup
|
||
│
|
||
▼
|
||
Storage Layout
|
||
│
|
||
▼
|
||
Atomic Updates
|
||
│
|
||
▼
|
||
Rollback
|
||
│
|
||
▼
|
||
Security
|
||
│
|
||
▼
|
||
Testing
|
||
│
|
||
▼
|
||
Production Deployment
|
||
```
|
||
|
||
While each chapter can be read independently, following the series in order provides a much deeper understanding of the complete system.
|
||
|
||
---
|
||
|
||
## Engineering Philosophy
|
||
|
||
This repository is intentionally different from product documentation.
|
||
|
||
Instead of presenting a single "correct" solution, every topic discusses:
|
||
|
||
- why a particular design exists;
|
||
- which problem it solves;
|
||
- what alternatives are available;
|
||
- what trade-offs each approach introduces;
|
||
- when another solution may be more appropriate.
|
||
|
||
Real-world engineering is rarely about choosing the only correct answer.
|
||
|
||
It is about understanding constraints and making informed decisions.
|
||
|
||
---
|
||
|
||
## The Reference Design
|
||
|
||
The architecture presented throughout this repository is a coherent reference design.
|
||
|
||
Real products may use different technologies or frameworks while following the same architectural principles.
|
||
|
||
For example, one project may use RAUC, another SWUpdate, and another a completely custom implementation.
|
||
|
||
The implementation details may differ.
|
||
|
||
The underlying engineering principles usually do not.
|
||
|
||
---
|
||
|
||
## Practical Examples
|
||
|
||
Where possible, theoretical discussions are accompanied by practical material, including:
|
||
|
||
- architecture diagrams
|
||
- boot sequence walkthroughs
|
||
- storage layout examples
|
||
- failure scenarios
|
||
- Raspberry Pi demonstrations
|
||
- QEMU-based experiments
|
||
- implementation notes
|
||
|
||
The objective is to connect high-level architecture with practical implementation.
|
||
|
||
Available now: [PlantUML diagrams](../diagrams/readme.md), a [C++ A/B trial boot simulation](../examples/simulations/ab-trial-boot/readme.md), and a [C++ interrupted installation model](../examples/simulations/interrupted-installation/readme.md). Chapters 03–05 have PNG previews; chapter 06 currently has sources only. Raspberry Pi and QEMU demonstrations are planned.
|
||
|
||
---
|
||
|
||
## Intended Audience
|
||
|
||
This repository is intended for:
|
||
|
||
- Embedded Linux developers
|
||
- Firmware engineers
|
||
- Embedded software engineers
|
||
- System architects
|
||
- Students learning embedded systems
|
||
- Engineers preparing for technical interviews
|
||
- Anyone interested in understanding OTA system design
|
||
|
||
No prior experience with OTA frameworks is assumed.
|
||
|
||
---
|
||
|
||
## How to Read This Repository
|
||
|
||
If you are new to OTA systems, simply start with Chapter 1 and continue in order.
|
||
|
||
If you already have embedded Linux experience, feel free to jump directly to topics that interest you.
|
||
|
||
If you are looking for implementation details, the accompanying examples provide practical demonstrations of the concepts discussed in the documentation.
|
||
|
||
---
|
||
|
||
## OTA at a Glance
|
||
|
||
The following diagram illustrates the overall update lifecycle that will be explored throughout this repository.
|
||
|
||
```text
|
||
OTA Server
|
||
│
|
||
Signed Update
|
||
│
|
||
┌───────────▼───────────┐
|
||
│ Download Manager │
|
||
└───────────┬───────────┘
|
||
│
|
||
Verify Signature
|
||
│
|
||
Verify Integrity
|
||
│
|
||
Install Update
|
||
│
|
||
Mark Boot Target
|
||
│
|
||
Reboot Device
|
||
│
|
||
Bootloader Decision
|
||
┌─────────┴─────────┐
|
||
│ │
|
||
Boot Success Boot Failure
|
||
│ │
|
||
▼ ▼
|
||
Commit Update Rollback
|
||
```
|
||
|
||
Each stage of this process will be examined in detail in the chapters that follow.
|
||
|
||
---
|
||
|
||
## Contributing
|
||
|
||
Contributions, suggestions, and discussions are welcome.
|
||
|
||
If you have ideas for improvements, additional examples, or alternative approaches, feel free to open an issue or submit a pull request.
|
||
|
||
---
|
||
|
||
## License
|
||
|
||
This repository is released under the MIT License.
|
||
|
||
See the LICENSE file for details.
|