Limits & behaviors

Hard limits (measured/enforced as of 2026-09-05; each is a real bound):

What	Bound	What happens at the bound
`cpus`	1–4 at launch	`400` before any host work
`memory_mb`	128–8192 at launch	`400`
writable disk	16 GiB sparse, fixed	`writable_size_bytes` other than 16 GiB → `400`
processes per sandbox	one per MiB of `memory_mb` (four for `runtime="vm"`), floor 256 / cap 4096 (1024 / 16384 for vm) — 1024 at the default 1 GiB; a cgroup pids cap, independent of `cpus`; `ulimit -u` is not it (root is exempt from RLIMIT_NPROC)	forks fail with `EAGAIN` inside the sandbox. A steady load recovers as processes exit. An exec or session whose processes reach the cap is treated as a fork storm and that exec’s process group is killed; the sandbox stays up and answers
sessions per sandbox	256 concurrent `session()` shells; the 257th open returns 409 `session limit (256) reached` (ConflictError). `close()` frees a slot.
container memory	guest RAM minus max(128 MiB, 10 %) reserved for the guest agent and kernel	a process over the cap is OOM-killed inside the sandbox; the agent survives and keeps answering
`exec` argv	128 KiB (kernel `MAX_ARG_STRLEN`)	`400`; ship bulk data via `stdin`
`exec` stdout / stderr	16 MiB per stream, text (UTF-8; invalid bytes become U+FFFD)	truncated: `stdout_truncated` / `stderr_truncated` `true` (SDK `ExecResult.truncated`) + an inline notice; write large or binary output to a file and read it back
synchronous `exec`	~110 s at the edge	the call fails; use `run(…, background=True)`/sessions for long work
request budget	per organization, per request class — the documented numbers are the EFFECTIVE fleet-wide budget	`429` + `Retry-After` (see status codes)

Rate limits are per organization per minute (new organizations: 300 acquisitions — creates/snapshots/forks/exposes/templates/exports — and 12,000 other operations; DELETE is never limited). Each figure is a per-minute guarantee enforced as a fixed-window bucket per gateway replica (two), refilled in full each minute — so sustained throughput can measure up to ~2× the figure before any 429, and after a 429 the budget returns all at once; a 429 carries Retry-After, and successful responses carry x-ratelimit-remaining (nv.rate.acquire / nv.rate.ops in the SDK).

Behaviors

Idle sleep policy (since 2026-09-07). The platform never auto-sleeps a sandbox that is doing work: a process that outlived its exec, guest CPU above the idle floor, live network connections, or an exposed port all count as work. Only a sandbox idle by every measure, with no API call for ~60 s, is slept; the next call wakes it transparently. No maximum hold. Fork bombs are contained to their sandbox; a watchdog freezes and kills the storm near the pids cap and the sandbox’s agent normally survives (measured 2026-09-05/07). If the guest wedges anyway: SandboxUnhealthyError → reboot() or delete. archive/unarchive is a true resume: processes, sockets and memory continue. /tmp is ordinary writable-disk space (not RAM), so it survives archiving and counts toward the disk. delete() returns before the guest is gone: the record answers 404 immediately (repeat DELETE = no-op 204) while the host tears down asynchronously — typically under a second. Its URL and in-flight execs fail during that window; that is teardown, not a leak. Network policy. Link-local 169.254.0.0/16 is blackholed for every sandbox. disable_internet is inherited by snapshots’ restores and fork children; a no-egress connect blocks until the client’s own timeout (no fast rejection) — give such clients short connect timeouts. Environment variables cannot be set per sandbox at create: bake them into the image or set them per run (run("VAR=value cmd") or a session’s export). Clock. Guests boot with clocksource=kvm-clock: CLOCK_MONOTONIC is consistent across vCPUs.

Harbor benchmarks

The nanovm-harbor wheel (/sdk/ on the console) is a Harbor environment provider (--env nanovm_environment:NanoVMEnvironment); it handles template builds, retries, compose tasks, and ships python -m nanovm_prebuild images.txt. README inside the wheel or the repo’s integrations/harbor/.

Getting Started

Guides

Concepts

Reference

Limits & behaviors

Behaviors

Harbor benchmarks

​Behaviors

​Harbor benchmarks

Behaviors

Harbor benchmarks