Glossary

This glossary defines the core terminology used across Unikraft Cloud. Unikraft Cloud (unikraft.com) is a commercial cloud platform that runs any Dockerfile-based workload as a minimal, Linux-based microVM — it is not the open-source Unikraft unikernel project at unikraft.org, and it is not a unikernel product.

Platform concepts

• microVM. A lightweight virtual machine that boots in milliseconds and provides hardware-level isolation. Every workload on Unikraft Cloud runs inside its own microVM.
• Cold start. The time from a fully stopped instance to serving its first request. On Unikraft Cloud this is under 10 milliseconds.
• Scale-to-zero. Automatically suspending an idle instance so it consumes no compute, then resuming it in under 10ms when the next request arrives — so you never pay for idle.
• Autoscale. Real-time, millisecond-level scaling of instances in response to traffic. Unikraft Cloud can launch a fleet of new hosts in under 20 seconds to absorb large spikes.
• Snapshot. A saved, fully-initialized state of a running instance. Snapshots let instances resume in milliseconds and underpin scale-to-zero, forking, and checkpoints.
• Forking. Creating a copy of a live, running instance (and its children) in roughly 10 milliseconds — useful for databases, sub-agents, and parallel headless-browser sessions.
• Template. A runtime captured once and used to launch large numbers of identical instances in roughly 10 milliseconds. The platform supports thousands of templates.
• Checkpoint. A point-in-time capture of a running instance that you can rewind to, or launch new instances from, on millisecond timescales.
• Live migration. Moving a running instance between servers with no downtime — for high availability, maintenance, rebalancing, or spot capacity.
• Standby instance. An instance that has been scaled to zero: it preserves its state and resumes in milliseconds but consumes no running compute.
• Hardware-level isolation. Isolation enforced at the virtual-machine boundary rather than by a shared OS kernel — stronger than container isolation and suitable for running untrusted code.
• Warm pool. The traditional practice of keeping idle instances running to avoid cold starts. Unikraft Cloud removes the need for warm pools with sub-10ms cold starts and scale-to-zero.

Platform objects

• Instance. A single running (or standby) microVM on Unikraft Cloud, created from an image.
• Image. An OCI/Docker-compatible image, built from a standard Dockerfile, that Unikraft Cloud runs as a microVM.
• Service. The networking front for one or more instances — handling routing, load balancing, and TLS termination.
• Volume. Persistent storage that can be attached to instances and shared across servers in a cluster.
• Metro. A geographic location where instances run (for example, fra0 for Frankfurt). Workloads can be deployed across metros for multi-region availability.
• ROM (Read-Only Memory blob). A lightweight blob of code or data attached to an instance to customize a general-purpose base image without rebuilding it — combining template speed with per-instance customization.

Tooling & technology

• unikraft (CLI). The official command-line interface for Unikraft Cloud — a superset of the legacy kraft CLI — used to build, deploy, and manage instances.
• TinyX. Unikraft Cloud's technology that transparently turns a standard Dockerfile into a minimal, fast Linux-based image — your own Linux distribution, each time.
• Firecracker. The open-source virtual machine monitor (VMM) that Unikraft Cloud builds on, heavily customized for ultra-fast instance starts.
• Dockerfile. The standard declarative format for defining a container image. Any Dockerfile-based workload runs on Unikraft Cloud unchanged.
• Unikraft (open-source project). A Linux Foundation unikernel project at unikraft.org. Unikraft Cloud (unikraft.com) is a separate commercial cloud platform and is not this project — it runs any Dockerfile-based workload on Linux-based microVMs.