MicroVMs Explained: The Perfect Balance Between Containers and Virtual Machines

What is a MicroVM?

A microVM is a lightweight virtual machine that combines the security and isolation of traditional VMs with the resource efficiency of containers. It’s designed to run multiple high-performance, secure workloads concurrently on a single machine.

Firecracker: The Leading MicroVM Technology

AWS created Firecracker, written in Rust, to address the limitations they faced with their Lambda and Fargate services. They needed faster scaling, lower latency, and better security without compromising performance. Firecracker was open-sourced in 2018 and uses Linux KVM (Kernel-based Virtual Machine) for virtualization.

Where to use MicroVMs

1. Isolated Execution Environments for Sensitive Workloads

Use Case: Run high-risk workloads such as code from third-party vendors, AI/ML models, or financial simulations in isolated environments.

They provide hardware-level isolation with minimal overhead — better than containers alone, but lighter than full VMs.

Example: Risk modeling engines or fraud detection algorithms that require isolation from other banking systems.

2. Secure Multi-Tenant PaaS in Private Cloud

Use Case: Build a Platform-as-a-Service for internal teams, where each team gets isolated compute environments.

They ensure tenant isolation and fast provisioning, while keeping the resource cost low.

Example: Internal DevOps platform for development and testing of microservices by various business units.

3. Zero Trust & Confidential Computing

Use Case: Combine with trusted execution environments (e.g., AMD SEV, Intel TDX) for encrypted computation.

Some MicroVM frameworks (like Firecracker or Kata Containers) can run in confidential compute mode.

Example: Run machine learning on customer data with encryption-in-use, satisfying zero trust policies.

When NOT to Use MicroVMs

High-Frequency Trading - Microsecond latency requirements favor direct container deployment.

ML Training - GPU-intensive workloads benefit more from bare metal or container solutions.

Legacy Applications - Monolithic applications without security concerns work better with traditional deployment methods.

Key Features of MicroVMs

Minimalist Design: Excludes unnecessary devices and functionality, maintaining a small memory footprint (< 5 MiB)

Fast Startup: Can create up to 150 microVMs per second per host, with application code starting in just 125ms

Strong Isolation: Provides VM-level security isolation while being much more lightweight than traditional VMs

Resource Efficiency: Supports compute oversubscription, allowing more efficient use of resources

Comparison: MicroVMs vs Containers vs VMs

- MicroVMs: Best of both worlds - stronger isolation than containers, more efficient than full VMs

- Containers: Fastest and most resource-efficient, but share the host OS kernel

- Traditional VM*: Strongest isolation but highest resource overhead

Benefits

1. Security: Small attack surface with jailed processes using cgroups and seccomp BPF

2. Speed: Sub-125ms launch times at scale

3. Scalability: Small memory footprint allows many microVMs per server

Practical Applications

MicroVMs are ideal for serverless computing, multi-tenant workloads, and scenarios requiring strong isolation with minimal overhead. You can use them to automatically run customer workloads with both security and performance.

Technical Architecture Deep Dive

Core Components:

Virtual Machine Monitor (VMM) - Firecracker acts as a minimalist VMM that creates and manages microVMs, written in Rust for memory safety and performance.

Linux KVM Integration - Leverages the Linux Kernel-based Virtual Machine for hardware virtualization support, running entirely in userspace.

Guest Kernel - Each microVM runs its own Linux kernel, providing complete OS-level isolation from the host system.

Hardware Virtualization Layer

CPU Virtualization - Uses Intel VT-x or AMD-V extensions to create isolated execution contexts for each microVM.

Memory Management - Implements hardware-assisted memory virtualization with minimal overhead, typically under 5MB per instance.

I/O Virtualization - Provides paravirtualized network and block devices for efficient host-guest communication.

Firecracker Architecture

RESTful API - Controls microVM lifecycle through HTTP endpoints for creating, configuring, and managing instances.

Jailer Process - Provides additional security isolation using Linux cgroups, namespaces, and seccomp-BPF filters.

Rate Limiting - Built-in bandwidth and IOPS controls prevent resource contention between microVMs on the same host.

Boot Process

Fast Boot Path - Bypasses traditional BIOS/UEFI by directly loading a Linux kernel, eliminating firmware overhead.

Minimal Device Model - Exposes only essential virtualized devices (network, block storage, serial console) for faster initialization.

Memory Balloon - Dynamically adjusts memory allocation without guest OS restart for efficient resource utilization.

Networking Architecture

Tap Interface - Each microVM gets a dedicated tap device connected to the host's network bridge.

Traffic Shaping - Implements ingress/egress bandwidth controls at the hypervisor level for predictable performance.

Metadata Service - Provides secure configuration exchange between host and guest without network exposure.

Security Model

Hardware Isolation - Leverages CPU virtualization features to create strong memory and execution boundaries.

Syscall Filtering - Restricts Firecracker process to a minimal set of system calls using seccomp-BPF.

Resource Constraints - Enforces CPU, memory, and I/O limits through Linux control groups integration.