Exploring Unikernel Technology in Real-Time Environments

Master's Thesis - 2024/2025
FCTUC - Universidade de Coimbra

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📖 Introduction and Objectives

This thesis investigates the viability of unikernels in real-time environments. The primary goal is to evaluate whether these highly specialized, lightweight systems can meet the strict determinism and predictability requirements of real-time applications in fields like aviation, medicine, and finance.

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🧠 State of the Art

What is a Unikernel?

A unikernel is a minimalistic, single-address-space system containing only the OS components and libraries required to run a specific application. Unlike traditional OSs, they eliminate unnecessary functionalities, reducing attack surfaces and resource usage.

• Left (General Purpose OS): Includes generic components, with a subset (highlighted) used by the application.
• Right (Unikernels): Contains only essential components (highlighted) for a single application.

Real-Time Environments

• Definition: Systems that guarantee task execution within strict deadlines.
• Key Requirements: Predictability, determinism, fault tolerance.
• Types: Hard (zero tolerance), Firm (tolerate minor delays), Soft (tolerate delays with degraded performance).

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🔍 Exploratory Work

Unikernel Framework Selection

• Initial Pool: 17 frameworks identified.
• Selection Criteria: Active repositories, documentation, community support, framework diversity.
• Final Selection: 6 frameworks (see table below).

Unikernel	Type	Execution Environment	Languages	Last Update
HermiTux	POSIX	QEMU/KVM, Uhyve	C/C++, Python, Lua, Rust	17/11/2023
MirageOS	Non-POSIX	UNIX, Xen, KVM, FreeBSD	OCaml	10/04/2024
Nanos	POSIX	QEMU/KVM, XEN, ESXi, Amazon EC2, Google Cloud, HyperV, Oracle, RPI4	C/C++, Go, Java, Node.js, Python, PHP, Ruby, Ruby	17/04/2024
OSv	POSIX	QEMU/KVM, Firecracker, Cloud Hypervisor, Xen, VMWare, VirtualBox, Hyperkit	C/C++, Java, Node.js, Ruby, Erlang, Go, Rust	19/03/2024
UKL	POSIX	QEMU/KVM	C/C++	08/09/2023
Unikraft	POSIX	QEMU/KVM, XEN	C/C++, Python, Go, Rust, Lua	05/04/2024

Last updated: 07 June 2024

🧪 Tests with Unikernels

Initial Results

Project Name	Hello Word	Small Application	Cyclictest	Jitterdebugger
Hermitux	✓	✓	✗	✗
Mirage OS	✓	✓	✗	✗
Nanos	✓	✓	✗	✗
OSv	✓	✓	✗	✗
UKL	✓	✓	✗	✗
Unikraft	✓	✓	✗	✗

Key Challenges

• MirageOS: Requires OCaml rewrites (non-POSIX limitation).
• POSIX Unikernels: Critical syscalls missing (e.g., clock_nanosleep).

Breakthrough: Syscall Analysis

• Method: Mapped syscalls required by Cyclictest/Jitterdebugger against unikernel capabilities.
• Solution: Implemented missing syscalls.

Final Results for Exploratory Work

Project Name	Hello Word	Wind Vibration	Cyclictest	Jitterdebugger
Nanos	✓	✓	✗	✗
OSv Modified	✓	✓	✗	✗

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💡 Proof of Concept: AppBox

Concept

A Linux-based minimalist system bridging the gap between unikernels and traditional OSs:

• Kernel: Full Linux kernel (ensures syscall compatibility).
• Minimalism: Stripped-down userspace (smaller footprint than conventional OSs).

Comparison:

System	Kernel Completeness	Syscall Support	Specialization
Traditional OS	Full	Complete	Low
Unikernel	None	Partial	High
AppBox	Full	Complete	Medium

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Last updated: 12 February 2025