Building Your Own Serverless Platform: Firecracker MicroVMs on Linux KVM
Container isolation is a lie we tell ourselves to sleep at night. If you have been in the trenches of multi-tenant architecture long enough, you know that cgroups and namespaces are not a fortress; they are a picket fence. All it takes is one kernel vulnerability or a noisy neighbor saturating the memory bus to bring your "isolated" environment to its knees.
It is July 2024. We are seeing a shift away from massive Kubernetes clusters for ephemeral workloads. The industry is moving toward MicroVMs. Specifically, Firecracker. This is the technology powering AWS Lambda and Fargate. It offers the speed of containers with the hardware virtualization security of a traditional VM.
Why should you care? Because vendor lock-in is expensive, and data sovereignty laws in Europe (specifically Norway) are tightening. If you want the efficiency of serverless without shipping your data to a US-owned region that might trip over Schrems II, you build it yourself. Here is how we do it on a robust Linux environment.
The Architecture: Why Firecracker?
Firecracker, written in Rust, uses the Linux Kernel-based Virtual Machine (KVM) to create microVMs. Unlike QEMU, which is a Swiss Army knife capable of emulating legacy floppy drives, Firecracker is a scalpel. It emulates a keyboard (to reset), a minimal network device, and a block device. That is it.
The result?
1. Boot time: < 125 ms.
2. Memory overhead: < 5 MiB per microVM.
Pro Tip for Norwegian Devs: Running high-density microVMs requires serious I/O throughput. Standard SATA SSDs will choke during the "boot storms" typical of serverless workloads. Always verify your provider uses NVMe storage. On CoolVDS, our NVMe arrays are configured specifically to handle high IOPS consistency, essential for this architecture.
Prerequisites and Environment Check
You cannot run Firecracker on just any container. You need access to /dev/kvm. This means you need a bare-metal server or a VPS provider that supports nested virtualization (giving you a VMX flag passed through to the guest).
First, verify your host supports hardware virtualization:
lscpu | grep -e 'Virtualization' -e 'Flags' | grep -E 'vmx|svm'
If that returns output, check access to the KVM device:
[ -r /dev/kvm ] && [ -w /dev/kvm ] && echo "OK" || echo "No KVM access"
If you see "No KVM access" and you are on a VPS, submit a ticket or switch providers. CoolVDS instances are built on KVM and support the necessary instruction sets for modern virtualization workloads.
Step 1: Getting the Binary
Let's grab the latest release (v1.7.0 as of mid-2024) and set it up. Do not use package managers; get the binary directly to control the version.
release_url="https://github.com/firecracker-microvm/firecracker/releases"
latest=$(basename $(curl -fsSLI -o /dev/null -w %{url_effective} ${release_url}/latest))
arch=$(uname -m)
curl -L ${release_url}/download/${latest}/firecracker-${latest}-${arch}.tgz | tar -xz
mv release-${latest}-${arch}/firecracker-${latest}-${arch} /usr/local/bin/firecracker
chmod +x /usr/local/bin/firecrackerStep 2: Preparing the Guest Kernel and RootFS
Firecracker boots a Linux kernel. You need an uncompressed vmlinux binary. For the filesystem, we will use a minimal Alpine Linux image. This keeps our cold start times nearly instant.
# Download a pre-compiled kernel suitable for Firecracker
wget https://s3.amazonaws.com/spec.ccfc.min/img/quickstart_guide/x86_64/kernels/vmlinux-5.10.186
# Download a minimal ext4 root filesystem
wget https://s3.amazonaws.com/spec.ccfc.min/img/quickstart_guide/x86_64/rootfs/bionic.rootfs.ext4
# Rename for simplicity
mv vmlinux-5.10.186 vmlinux
mv bionic.rootfs.ext4 rootfs.ext4Step 3: Configuring the MicroVM
Firecracker is API-driven. You start the process, and it listens on a Unix socket. You don't configure it via command line arguments like QEMU. You send it JSON.
Terminal 1: Start Firecracker
rm -f /tmp/firecracker.socket
firecracker --api-sock /tmp/firecracker.socket
Terminal 2: Configure via API
We will set the boot source (kernel) and the root drive.
# 1. Set the Kernel
curl --unix-socket /tmp/firecracker.socket -i \
-X PUT 'http://localhost/boot-source' \
-H 'Accept: application/json' \
-H 'Content-Type: application/json' \
-d '{
"kernel_image_path": "./vmlinux",
"boot_args": "console=ttyS0 reboot=k panic=1 pci=off"
}'
# 2. Set the Root Filesystem
curl --unix-socket /tmp/firecracker.socket -i \
-X PUT 'http://localhost/drives/rootfs' \
-H 'Accept: application/json' \
-H 'Content-Type: application/json' \
-d '{
"drive_id": "rootfs",
"path_on_host": "./rootfs.ext4",
"is_root_device": true,
"is_read_only": false
}'Step 4: The Launch
This is the moment of truth. We instruct the API to power on the instance.
curl --unix-socket /tmp/firecracker.socket -i \
-X PUT 'http://localhost/actions' \
-H 'Accept: application/json' \
-H 'Content-Type: application/json' \
-d '{
"action_type": "InstanceStart"
}'
Check your first terminal. You should see the boot log flying by. It happens so fast that by the time your finger lifts off the Enter key, the VM is likely already at the login prompt.
Performance: MicroVMs vs. Containers
Why go through this hassle instead of just running Docker? Isolation depth and security posture. In a compliant environment—think handling Norwegian health data or financial records subject to Datatilsynet audits—shared kernel containers are a liability.
| Feature | Docker/Container | Firecracker MicroVM |
|---|---|---|
| Isolation | Shared Kernel (Namespaces) | Hardware Virtualization (KVM) |
| Startup Time | ~500ms - 2s | < 125ms |
| Memory Overhead | Varies (High) | < 5 MB |
| Attack Surface | Large (Full Syscall interface) | Minimal (Reduced device model) |
Network Latency and Local Infrastructure
Building a serverless platform is not just about the hypervisor. It is about where the packets physically travel. If your users are in Oslo or Bergen, hosting your microVMs in Frankfurt or Dublin introduces unnecessary latency (20-40ms round trip).
For real-time applications, you want your compute edge close to the NIX (Norwegian Internet Exchange). Hosting on CoolVDS ensures your traffic stays local, reducing latency to single digits for Nordic users. Furthermore, strict adherence to GDPR requires knowing exactly where your physical drives are spinning. With us, that data never leaves the jurisdiction you expect it to be in.
Summary
Firecracker brings the security of the cloud giants to your private infrastructure. It allows you to utilize every CPU cycle of your VPS without fearing that a compromised process will escape to the host. However, it demands a robust underlying host. High-performance NVMe storage and unrestricted KVM access are non-negotiable.
Do not let your infrastructure be the bottleneck for your code. If you are ready to build a high-density, secure compute platform, deploy a CoolVDS High-Performance KVM instance today and start compiling your future.