all posts
blog · topic

Firecracker and microVMs

Firecracker is the virtual machine monitor behind AWS Lambda and PandaStack's sandboxes: a minimal KVM-based VMM that boots a Linux guest with its own kernel in milliseconds. These posts explain how microVMs work, how they compare with containers, gVisor and Kata, and what it takes to run them as a platform.

Firecracker microVM sandboxes

193 posts

·10 min read

KVM Halt Polling Explained: Why an Idle microVM Can Burn a Core Doing Nothing

A guest with nothing to do executes HLT, and the host has to decide whether to block the vCPU thread or spin for a moment hoping an interrupt arrives. That decision is a module parameter, it is global to the host, and on a fleet of sleeping microVMs it quietly puts a floor under every CPU number you bill on.

firecrackerkvmhalt-polling
Ajay Kumar
·10 min read

kvm-clock vs TSC: How a Firecracker Guest Tells the Time, and What a Snapshot Does to It

A guest clock is not one thing. It is a rated list of clocksources, a shared memory page the host writes into, and a userspace fast path that silently becomes a trap when you pick wrong. Then you snapshot it, and the whole stack starts lying in a very specific way: TLS first, loudly.

firecrackerkvm-clockclocksource
Ajay Kumar
·10 min read

Firecracker vs Hyper-V Isolated Containers: Two Ecosystems, One Verdict

Microsoft shipped Hyper-V isolated containers because Windows containers on a shared kernel were not a boundary they would stand behind for other people's code. The Linux world shipped Firecracker, Kata and gVisor for exactly the same reason. Same verdict, opposite engineering — and one of them cannot run your Windows binary.

firecrackerhyper-vwindows-containers
Ajay Kumar
·11 min read

Best bare metal providers for Firecracker in 2026

Firecracker needs /dev/kvm, and that one requirement disqualifies most of the cheap compute on the market. The three tiers of hosting that can actually run it, what each gets wrong, and the 60-second check to run before you sign anything.

firecrackerbare-metalinfrastructure
Ajay Kumar
·11 min read

Letting Customers Run Their Own Container Image

“Bring your own container image” is a remote-code-execution endpoint with a product manager attached. The admission pipeline, the baked-RAM surprise, and why the escape surface you just inherited belongs to the kernel rather than to Docker.

containersocimulti-tenancy
Ajay Kumar
·10 min read

firecracker-containerd: Running OCI Images in MicroVMs, and What It Costs You

It lets you keep your images, your registry and your containerd tooling, and swap the thing at the bottom for a microVM. That is a genuinely small diff for a large change in blast radius — and it is still the wrong tool if what you wanted was a fast sandbox API.

firecrackercontainerdoci
Ajay Kumar
·10 min read

Firecracker vs FreeBSD Jails: Two Honest Answers to the Same Question

Jails predate Linux containers by a decade and are better designed than them. They also share the host kernel, which is the entire comparison. Everything else is downstream of that one sentence.

freebsdjailsfirecracker
Ajay Kumar
·10 min read

Can Firecracker Run Windows? No, and the Reason Is the Point

The answer is no, and it is not an oversight or a roadmap item. It falls out of the one decision that makes a microVM boot in milliseconds — and the set of guests Firecracker does support tells you exactly why.

firecrackerwindowsmicrovm
Ajay Kumar
·11 min read

Firecracker vs VMware ESXi: the Device Model Decides

Both words mean "hypervisor," and that is the last thing they have in common. ESXi's value is an enormous device model and a datacenter control plane; Firecracker's value is having neither. The whole comparison lives in that one trade.

firecrackervmwareesxi
Ajay Kumar

More posts in this topic