microsandbox 0.4.0

Python SDK for microsandbox — secure, fast microVM-based sandboxing.

microsandbox

Lightweight VM sandboxes for Python — run AI agents and untrusted code with hardware-level isolation.

The microsandbox Python package provides native bindings to the microsandbox runtime via pyo3. It spins up real microVMs (not containers) in under 100ms, runs standard OCI (Docker) images, and gives you full control over execution, filesystem, networking, and secrets — all from a simple async API.

Features

• Hardware isolation — Each sandbox is a real VM with its own Linux kernel
• Sub-100ms boot — No daemon, no server setup, embedded directly in your app
• OCI image support — Pull and run images from Docker Hub, GHCR, ECR, or any OCI registry
• Command execution — Run commands with collected or streaming output, interactive shells
• Guest filesystem access — Read, write, list, copy files inside a running sandbox
• Named volumes — Persistent storage across sandbox restarts, with quotas
• Network policies — Public-only (default), allow-all, or fully airgapped
• DNS filtering — Block specific domains or domain suffixes
• TLS interception — Transparent HTTPS inspection and secret substitution
• Secrets — Credentials that never enter the VM; placeholder substitution at the network layer
• Port publishing — Expose guest TCP/UDP services on host ports
• Rootfs patches — Modify the filesystem before the VM boots
• Detached mode — Sandboxes can outlive the Python process
• Metrics — CPU, memory, disk I/O, and network I/O per sandbox
• Typed — Frozen dataclasses, StrEnums, sealed event unions, .pyi stubs

Requirements

• Python >= 3.10
• Linux with KVM enabled, or macOS with Apple Silicon (M-series)

Supported Platforms

Platform	Architecture	Wheel tag
macOS	ARM64 (Apple Silicon)	macosx_11_0_arm64
Linux	x86_64	manylinux_2_28_x86_64
Linux	ARM64	manylinux_2_28_aarch64

Runtime binaries (msb + libkrunfw) are bundled in the wheel. One wheel per platform, all Python 3.10+ versions via abi3.

Installation

pip install microsandbox

Quick Start

import asyncio
from microsandbox import Sandbox

async def main():
    # Create a sandbox from an OCI image.
    sandbox = await Sandbox.create(
        "my-sandbox",
        image="alpine",
        cpus=1,
        memory=512,
    )

    # Run a command.
    output = await sandbox.shell("echo 'Hello from microsandbox!'")
    print(output.stdout_text)

    # Stop the sandbox.
    await sandbox.stop_and_wait()

asyncio.run(main())

Examples

Command Execution

from microsandbox import Sandbox

# Collected output.
output = await sandbox.exec("python3", ["-c", "print(1 + 1)"])
print(output.stdout_text)   # "2\n"
print(output.exit_code)      # 0

# Shell command (pipes, redirects, etc.).
output = await sandbox.shell("echo hello && pwd")
print(output.stdout_text)

# Full configuration via ExecOptions dict.
output = await sandbox.exec("python3", {
    "args": ["script.py"],
    "cwd": "/app",
    "env": {"PYTHONPATH": "/app/lib"},
    "timeout": 30.0,
})

# Streaming output.
handle = await sandbox.exec_stream("tail", ["-f", "/var/log/app.log"])
async for event in handle:
    match event.event_type:
        case "stdout": sys.stdout.buffer.write(event.data)
        case "stderr": sys.stderr.buffer.write(event.data)
        case "exited": break

await sandbox.stop_and_wait()

Filesystem Operations

fs = sandbox.fs

# Write and read files.
await fs.write("/tmp/config.json", b'{"debug": true}')
content = await fs.read_text("/tmp/config.json")

# List a directory.
entries = await fs.list("/etc")
for entry in entries:
    print(f"{entry.path} ({entry.kind})")

# Copy between host and guest.
await fs.copy_from_host("./local-file.txt", "/tmp/file.txt")
await fs.copy_to_host("/tmp/output.txt", "./output.txt")

# Check existence and metadata.
if await fs.exists("/tmp/config.json"):
    meta = await fs.stat("/tmp/config.json")
    print(f"size: {meta.size}, kind: {meta.kind}")

# Streaming read.
async for chunk in await fs.read_stream("/tmp/large-file.bin"):
    process(chunk)

Named Volumes

from microsandbox import Sandbox, Volume

# Create a 100 MiB named volume.
data = await Volume.create("my-data", quota_mib=100)

# Mount it in a sandbox.
writer = await Sandbox.create(
    "writer",
    image="alpine",
    volumes={"/data": Volume.named(data.name)},
    replace=True,
)

await writer.shell("echo 'hello' > /data/message.txt")
await writer.stop_and_wait()

# Mount the same volume in another sandbox (read-only).
reader = await Sandbox.create(
    "reader",
    image="alpine",
    volumes={"/data": Volume.named(data.name, readonly=True)},
    replace=True,
)

output = await reader.shell("cat /data/message.txt")
print(output.stdout_text)  # "hello\n"

await reader.stop_and_wait()

# Cleanup.
await Sandbox.remove("writer")
await Sandbox.remove("reader")
await Volume.remove("my-data")

Disk Image Volumes

from microsandbox import Sandbox, Volume, DiskImageFormat

# Mount a host disk image at a guest path. Format is inferred from the
# extension; pass `format=` to override. `fstype` is the inner FS agentd
# will mount; omit to let agentd autodetect.
sb = await Sandbox.create(
    "worker",
    image="alpine",
    volumes={
        "/data": Volume.disk("./data.qcow2", format=DiskImageFormat.QCOW2, fstype="ext4"),
        "/seed": Volume.disk("./seed.raw", readonly=True),
        "/scratch": Volume.tmpfs(size_mib=128, readonly=True),
    },
    replace=True,
)

Network Policies

from microsandbox import Network, Sandbox

# Default: public internet only (blocks private ranges).
sandbox = await Sandbox.create("public", image="alpine")

# Fully airgapped.
sandbox = await Sandbox.create(
    "isolated",
    image="alpine",
    network=Network.none(),
)

# Unrestricted.
sandbox = await Sandbox.create(
    "open",
    image="alpine",
    network=Network.allow_all(),
)

# DNS filtering.
sandbox = await Sandbox.create(
    "filtered",
    image="alpine",
    network=Network(
        block_domains=("blocked.example.com",),
        block_domain_suffixes=(".evil.com",),
    ),
)

Port Publishing

sandbox = await Sandbox.create(
    "web",
    image="python",
    ports={8080: 80},  # host:8080 → guest:80
)

Secrets

Secrets use placeholder substitution — the real value never enters the VM. It is only swapped in at the network layer for HTTPS requests to allowed hosts.

from microsandbox import Sandbox, Secret

sandbox = await Sandbox.create(
    "agent",
    image="python",
    secrets=[
        Secret.env("OPENAI_API_KEY",
                    value=os.environ["OPENAI_API_KEY"],
                    allow_hosts=["api.openai.com"]),
    ],
)

# Guest sees: OPENAI_API_KEY=$MSB_OPENAI_API_KEY (a placeholder)
# HTTPS to api.openai.com: placeholder is transparently replaced with the real key
# HTTPS to any other host with the placeholder: request is blocked

Rootfs Patches

Modify the filesystem before the VM boots:

from microsandbox import Patch, Sandbox

sandbox = await Sandbox.create(
    "patched",
    image="alpine",
    patches=[
        Patch.text("/etc/greeting.txt", "Hello!\n"),
        Patch.mkdir("/app", mode=0o755),
        Patch.text("/app/config.json", '{"debug": true}', mode=0o644),
        Patch.copy_dir("./scripts", "/app/scripts"),
        Patch.append("/etc/hosts", "127.0.0.1 myapp.local\n"),
    ],
)

Detached Mode

Sandboxes in detached mode survive the Python process:

# Create in detached mode.
sandbox = await Sandbox.create(
    "background",
    image="python",
    detached=True,
)
await sandbox.detach()

# Later, from another process:
handle = await Sandbox.get("background")
reconnected = await handle.connect()
output = await reconnected.shell("echo reconnected")

Context Manager

async with await Sandbox.create("temp", image="alpine", replace=True) as sb:
    output = await sb.shell("echo hello")
    print(output.stdout_text)
# Sandbox is automatically killed and removed on exit.

TLS Interception

from microsandbox import Network, Sandbox, TlsConfig

sandbox = await Sandbox.create(
    "tls-inspect",
    image="python",
    network=Network(
        tls=TlsConfig(
            bypass=("*.googleapis.com",),
            verify_upstream=True,
            intercepted_ports=(443,),
        ),
    ),
)

Metrics

from microsandbox import Sandbox, all_sandbox_metrics, MiB

sandbox = await Sandbox.create("metrics-demo", image="python")

# Per-sandbox metrics.
m = await sandbox.metrics()
print(f"CPU: {m.cpu_percent:.1f}%")
print(f"Memory: {m.memory_bytes // MiB} MiB")
print(f"Uptime: {m.uptime_ms / 1000:.1f}s")

# Streaming metrics.
async for m in sandbox.metrics_stream(interval=1.0):
    print(f"CPU: {m.cpu_percent:.1f}%")

# All sandboxes at once.
all_metrics = await all_sandbox_metrics()
for name, metrics in all_metrics.items():
    print(f"{name}: {metrics.cpu_percent:.1f}%")

Runtime Setup

from microsandbox import is_installed, install

if not is_installed():
    await install()  # Downloads msb + libkrunfw to ~/.microsandbox/

API Reference

Classes (native)

Class	Description
Sandbox	Live handle to a running sandbox — lifecycle, execution, filesystem
SandboxHandle	Lightweight database handle — use connect() or start() to get a live Sandbox
ExecOutput	Captured stdout/stderr with exit status
ExecHandle	Streaming execution handle — async iterator over events
ExecSink	Writable stdin channel for streaming exec
SandboxFs	Guest filesystem operations (read, write, list, copy, stat)
FsReadStream	Async iterator over file data chunks
FsWriteSink	Async context manager for streaming writes
Volume	Persistent named volume
VolumeHandle	Lightweight volume handle from the database
MetricsStream	Async iterator over metrics snapshots
PullSession	Async context manager for creation with pull progress

Factories (Python)

Class	Description
Volume.bind() / .named() / .tmpfs() / .disk()	Volume mount configuration
Network.none() / .public_only() / .allow_all()	Network presets
Secret.env()	Secret entry with host allowlist
Patch.text() / .mkdir() / .copy_file() / .append() / ...	Pre-boot filesystem modifications
Image.oci() / .bind() / .disk()	Explicit rootfs source configuration
Rlimit.nofile() / .cpu() / .as_() / ...	POSIX resource limits

Enums (Python StrEnum)

Enum	Values
PullPolicy	ALWAYS, IF_MISSING, NEVER
LogLevel	TRACE, DEBUG, INFO, WARN, ERROR
SandboxStatus	RUNNING, STOPPED, CRASHED, DRAINING, PAUSED
Action	ALLOW, DENY
Direction	EGRESS, INGRESS
Protocol	TCP, UDP, ICMPV4, ICMPV6
DestGroup	LOOPBACK, PRIVATE, LINK_LOCAL, METADATA, MULTICAST
ViolationAction	BLOCK, BLOCK_AND_LOG, BLOCK_AND_TERMINATE
FsEntryKind	FILE, DIRECTORY, SYMLINK, OTHER
RlimitResource	CPU, FSIZE, NOFILE, AS, ... (16 variants)

Dataclasses (Python, frozen)

Type	Description
ExecOptions	Full execution options (args, cwd, env, timeout, tty, rlimits)
AttachOptions	Attach options (args, cwd, env, detach_keys)
ExitStatus	Exit code and success flag
MountConfig	Volume mount (bind, named, or tmpfs)
PatchConfig	Pre-boot filesystem modification
SecretEntry	Secret binding to env var with host allowlist
NetworkPolicy	Custom network policy with rules
TlsConfig	TLS interception options
Network	Full network configuration
Rule	Network policy rule
RegistryAuth	Docker registry credentials
Size	Memory/storage size value type
Rlimit	POSIX resource limit

Event Types (Python, sealed unions)

Type	Variants
ExecEvent	StartedEvent, StdoutEvent, StderrEvent, ExitedEvent
PullProgress	Resolving, Resolved, LayerDownloadProgress, LayerDownloadComplete, LayerExtractStarted, LayerExtractProgress, LayerExtractComplete, LayerIndexStarted, LayerIndexComplete, PullComplete

Functions

Function	Description
is_installed()	Check if msb and libkrunfw are available
install()	Download and install runtime dependencies
all_sandbox_metrics()	Get metrics for all running sandboxes
version()	Return the SDK version string

Development

Prerequisites

• Rust (2024 edition)
• uv (Python package manager)
• maturin (uv tool install maturin)

Setup

cd sdk/python
uv sync --group dev

Build the extension

maturin develop --release

Run tests

uv run pytest tests/

Run an example

uv run --project sdk/python python examples/python/root-oci/main.py

Lint

uv run ruff check .

License

Apache-2.0