What Is a Micro VM (Micro Virtual Machine)?

Introduction

A Micro VM (Micro Virtual Machine) represents a significant evolution in virtualization technology. It's a lightweight, highly efficient form of virtual machine that provides the security benefits of traditional VMs while approaching the performance and resource efficiency of containers. As cloud computing and serverless architectures become increasingly prevalent, Micro VMs offer an optimal balance between isolation, security, and resource utilization.

Key Characteristics of Micro VMs

Micro VMs are defined by several distinctive features:

1. Minimalist Design: They include only essential components needed to run applications, eliminating unnecessary OS services and drivers.

2. Fast Boot Times: Micro VMs can start in milliseconds rather than seconds or minutes required by traditional VMs.

3. Small Memory Footprint: They typically require only a few MBs of memory overhead per instance.

4. Hardware-based Isolation: Like traditional VMs, they leverage hardware virtualization for strong security boundaries.

5. Streamlined Kernel: They run with minimal, often customized kernels optimized for specific workloads.

6. Immutable Infrastructure: Most Micro VM implementations treat the VM as immutable, improving security and predictability.

How Micro VMs Work

Micro VMs achieve their efficiency through several architectural innovations:

• Specialized Hypervisors: Purpose-built hypervisors like AWS's Firecracker and Google's gVisor focus exclusively on Micro VM functionality.
• Paravirtualization: Many Micro VMs use paravirtualized I/O for improved performance.
• Minimal Guest OS: Rather than full operating systems, Micro VMs often run minimalist Linux distributions or unikernels.
• Shared Kernel Resources: Some implementations intelligently share kernel resources between VMs where it doesn't compromise isolation.

Micro VMs vs. Traditional VMs vs. Containers

Popular Micro VM Technologies

Several technologies have emerged in the Micro VM space:

Firecracker

Developed by AWS for their Lambda and Fargate services, Firecracker is an open-source virtualization technology specifically designed for creating and managing secure, multi-tenant container and function-based services. It leverages KVM to create minimalist VMs in a fraction of a second.

Kata Containers

Kata Containers combines the security advantages of VMs with the speed and manageability of containers. It uses hardware virtualization to provide stronger workload isolation while maintaining compatibility with the container ecosystem.

QEMU-microvm

A specialized mode of the popular QEMU emulator designed for creating lightweight, high-performance virtual machines suitable for cloud-native environments.

Cloud Hypervisor

An open-source VMM (Virtual Machine Monitor) written in Rust, designed specifically for running modern cloud workloads with minimal overhead.

Use Cases for Micro VMs

Micro VMs excel in several areas:

1. Serverless Computing: Perfect for function-as-a-service platforms where quick startup and efficient resource usage are critical.

2. Multi-tenant Environments: Provides stronger isolation between tenants than containers while maintaining good density.

3. Edge Computing: Their small footprint makes them ideal for resource-constrained edge devices.

4. Security-critical Applications: When container isolation isn't sufficient but traditional VMs are too resource-intensive.

5. CI/CD Environments: For running build jobs in clean, isolated environments that start quickly.

Benefits of Micro VMs

The advantages of Micro VMs include:

• Enhanced Security: Hardware-level isolation helps prevent privilege escalation attacks.
• Resource Efficiency: Lower overhead compared to traditional VMs means higher workload density.
• Speed: Fast boot times enable on-demand computing models.
• Cost Effectiveness: Better resource utilization can reduce infrastructure costs.
• Compatibility: Many solutions maintain compatibility with existing container workflows.

Limitations and Challenges

Despite their advantages, Micro VMs do have some limitations:

• Limited OS Support: Most Micro VM technologies primarily support Linux workloads.
• Specialized Tooling: May require learning new deployment and management tools.
• Maturity: Some implementations are relatively new compared to established virtualization technologies.
• Feature Set: May lack some advanced features of full VMs like live migration.

Micro VMs in Modern Cloud Architecture

Micro VMs have become a foundational component in modern cloud architecture, particularly in:

• Cloud Provider Services: Powers many serverless offerings from major cloud providers, with AWS Lambda and Fargate being prime examples built on Firecracker microVMs.
• Kubernetes Environments: Projects like KubeVirt and Kata Containers bring Micro VM isolation to Kubernetes.
• Hybrid Architectures: Enables new patterns that blend VM security with container workflows.
• Serverless Platforms: Many modern serverless providers run workloads in microVMs to optimize resource usage while maintaining strong isolation.

Firecracker: A Leading Micro VM Implementation

Firecracker deserves special attention as one of the most widely adopted microVM technologies:

• Origin: Developed by AWS specifically to optimize their serverless offerings (Lambda and Fargate)
• Implementation: Written in Rust for security, flexibility, and memory efficiency
• Release: Open-sourced under Apache 2.0 license in 2018
• Performance: Achieves impressive benchmarks including:
  • Creation of up to 150 microVMs per second per host
  • Application code initiation in under 125ms
  • Memory footprint under 5 MiB per instance
• Security: Uses "jailer" companion program that leverages cgroups and seccomp BPF to strictly limit system call access

Deploying Workloads in Micro VMs

One of the key advantages of microVMs is their versatility in workload deployment:

• Any function or container workload can run inside a microVM
• Many cloud providers automatically provision microVMs to run serverless and container workloads
• Resource management is optimized through built-in rate limiters that enable flexible distribution of resources across microVMs on a single host
• Supports a variety of processor architectures including 64-bit Intel, AMD, and ARM processors

Conclusion

Micro VMs represent a significant advancement in virtualization technology, bridging the gap between traditional virtual machines and containers. They provide an optimal balance of security, performance, and resource efficiency for many modern workloads. Don't be fooled by the "micro" name - these lightweight VMs pack considerable power by combining the density and speed of containers with the security and isolation of traditional VMs.

As cloud computing continues to evolve, Micro VMs are playing an increasingly important role in securing and optimizing application deployment, particularly in the serverless space. They enable cloud providers managing bare metal servers to run more workloads with significantly less overhead while maintaining strong isolation barriers between tenants.

For organizations evaluating their virtualization strategies, understanding the capabilities and appropriate use cases for Micro VMs is essential for making informed architectural decisions in an increasingly complex cloud landscape. Particularly for workloads that require both the security benefits of VMs and the efficiency of containers, microVMs offer an compelling technological solution.