---
title: Fleets, brokers & compute
description: How the broker schedules sessions onto a pool of cloud machines across pluggable compute backends — and why provider is not the same as harness.
status: verified
sidebar:
  order: 2
---

Three words describe where a session runs: **fleet**, **broker**, and **compute
provider**. Getting these straight makes the rest of Sessions legible.

## Fleet

A **fleet** is your org's pool of ephemeral session machines. It has settings
you control — pool size, idle and inactivity timeouts, the default agent and
model, the default personality, and how credentials are distributed. See the
[configuration reference](/sessions/reference/config/).

## Broker

The **broker** is the orchestrator. It keeps the warm pool, claims a machine
when a session starts, provisions it, and runs the Slack / Discord surfaces
and the HTTP API. You don't operate the broker directly; you configure your
fleet and start sessions, and the broker does the scheduling. Each org gets
its own single-tenant broker at `<org>.norisessions.com`.

## Compute provider (not the same as harness)

Two independent axes are easy to confuse — keep them apart:

- **Compute provider** — *where the VM runs*. The backend is pluggable behind
  one contract, selected per fleet: **Sprites** (Fly) is the default, and
  **Modal** is the alternative. A "sprite" is one Fly VM — it is *a* backend,
  not a synonym for "session machine."
- **Harness** — *what runs inside the VM*. The coding agent: Claude Code,
  Codex, Gemini, or a custom agent. Chosen per session.

So "any compute" and "any harness" are two separate promises. You can run
Claude Code on Modal, or Codex on Sprites — the axes don't constrain each
other.

:::note
Which backend a fleet uses is a fleet-level choice, not something you set per
run — and switching it drains and rebuilds the pool. See the
[configuration reference](/sessions/reference/config/).
:::

## Next steps

- [What is a session](/sessions/concepts/what-is-a-session/) — the lifecycle a machine moves through.
- [Harnesses & personalities](/sessions/concepts/harnesses-and-personalities/) — the other axis: what runs inside the VM.
- [Configuration reference](/sessions/reference/config/) — every fleet-level knob.