Running One Agent Somewhere Else

Sometimes a single seat needs to be somewhere the rest of the company is not: a support agent that must reach an internal API only one VPC can see, an engineer whose MCP server drives a licensed binary installed on one host, a seat that needs a GPU, a lab network, or a database behind a jump host.

You do not move the company for that. You start one more Crewlet process on that host, tell it what it is, and pin that one role to it. Everything else — the API, the webhooks, the scheduler, the other agents — stays exactly where it is. This shape is called a satellite: a node that runs agents, holds no company-wide duty, and terminates no inbound traffic.

A satellite comes in two shapes, and the difference is the data role:

	`roles: [seats]` — stateless	`roles: [data, seats]` — holds data
Its store	Scratch: deleted at every boot, and no copy of the tracker or knowledge base	Its own full copy of the replicated estate
Its broker	A leaf of the members’ — no JetStream, no replica, no vote	A cluster member, holding replicas (a data node on a leaf is refused)
Disk it needs	Its seats’ memory and working rows, nothing else	The whole company’s history
Its seats’ tools	Read and write through a data node, over the broker	Read and write its own copy, through the same router
Replacing it	Delete it and start another — it keeps nothing	A member leaving and joining

Which of the two its broker is — its broker kind — comes from its stream block, never from its roles: stream.leaf.urls makes it a leaf, and every node advertises the kind it runs on its presence (crewlet fleet broker list, or the Broker column on Settings › Nodes). See The broker: members and leaves.

Stateless is what you want for an agent host you intend to keep small and disposable: it can be rebuilt from its Tier A file alone, holds no raft state, and restarts in seconds whatever the company’s size. Its price is that its seats need a data node to answer — see what a satellite still needs.

A satellite is a normal crewlet run with roles subtracted, not a lighter agent-only binary. Either shape still needs to reach the fleet’s broker. If that is not possible from where you want the agent, this is not the mechanism you want.

What actually moves

Pinning a seat moves the whole seat, which is the point — an agent is not a request handler you can route, it is a place where things run:

Moves to the satellite	Stays on the core
The agent instance, its state and its turns	The HTTP API, the dashboard, every integration’s webhooks
Its per-role MCP servers, spawned as child processes of the node that claimed the seat	The scheduler tick, the retention sweep, the sandbox waiter, skill clustering and curation
Its LLM calls, its knowledge searches, its tool calls	Every other seat’s agents and MCP servers
Its sandbox launches, if the role is sandboxed	The company config, the leases and the ledgers — all shared, in the coordination slot

The MCP row is the one that makes this feature what it is. A seat’s stdio MCP servers are children of the process holding its lease, so “pin the seat” and “run its tools over there” are the same act. That is also why the mechanism cannot be a routing trick: the tools are not somewhere the request can be forwarded to, they are somewhere the agent has to be.

Work still reaches it normally. A trigger is published to the seat’s inbox topic, and the node holding that seat’s lease is the one consuming it — so nothing that publishes has to know where the agent is, and a Slack message routed to that agent works exactly as before.

Set it up

Three steps: say what the node is, say where the role belongs, start it.

1. Give the satellite a Tier A config

Only the Tier A file lives on the satellite. The company itself (roles, prompts, providers, integrations) comes from the fleet, so there is no company YAML to copy or keep in sync.

A stateless satellite on an embedded fleet:

# crewlet.yaml, on the satellite host
node:
  id: "${CREWLET_NODE_ID}"        # distinct and stable — sat-eu-1
  roles: [seats]                  # agents only: no data, no API, no duties
  labels:
    zone: eu                      # what a role will select on
  max_concurrent: 4               # this host runs one or two seats, not a
                                  #   company's worth — see below

store:
  path: "/var/lib/crewlet/sat-eu-1.db"
  scratch: true                   # deleted at every boot — required without
                                  #   the data role, and it says so twice

stream:
  leaf:
    urls:                         # any member's leaf listener will do
      - "nats-leaf://node-a.internal:7422"
      - "nats-leaf://node-b.internal:7422"

coordination:
  type: embedded-kv               # the fleet's replicated KV, reached over
                                  #   the same link

There is no stream.store_dir here, and there must not be: a leaf runs no JetStream, so it has no stream store to keep, and Tier A refuses one beside stream.leaf.urls. Every stream the satellite’s seats use lives on the members, in theirs — which is also why crewlet validate raises no in-memory stream warning for this file.

The members open that listener with stream.leaf.port, and a member that opens one must persist (stream.store_dir), as every member of a fleet must: the nodes that join it keep nothing, so it keeps everything they do.

# on node-a and node-b — alongside their existing cluster block
stream:
  store_dir: /var/lib/crewlet/stream
  leaf:
    port: 7422                    # where stateless nodes join

A leaf port something else already holds is refused when the member starts, by name, as a taken route port is (see Every node embeds a member of one cluster). NATS does not fail when it cannot bind the listener — it logs the error and the member never becomes ready — so the engine probes the port first:

leaf listener port taken: stream.leaf.port 7422 is already in use on
every interface, so no stateless node could join the fleet through this
member — free that port or give this node a different one

On an external NATS cluster there is no leaf to configure: a stateless node dials the cluster as every node does, and keeps store.scratch: true and roles: [seats].

A satellite that holds data is the same file with roles: [data, seats], a durable store (no scratch) and a cluster member’s stream.cluster block and stream.store_dir instead of stream.leaf — see Running a Fleet. It joins the broker as a voter: mind the five-member ceiling before adding one to a fleet that already has five.

${VAR} references are resolved in node.labels and node.id like anywhere else, so an orchestrator injects both from the environment without templating the file. There is a -roles flag for the same reason; labels have no flag, because ${VAR} already covers it.

api.port can stay set, and one config file works for both shapes: a node without the ingress role binds it for its probes alone — /health and /ready — and serves no API, no dashboard and no webhook on it (api_probes_listening). Every other path answers 404, or 401 for a write or an always-guarded prefix, exactly as an unknown path does on an ingress node. The one route it adds is for a seat in agent mode: its box calls the seat’s tools back over /mcp/{token}, and only the node that runs the seat can answer, so a satellite with CREWLET_MCP_BRIDGE_URL set serves that route (tool_bridge=true on the same line) — beside the probes, or on api.public.port when the file sets one (public_addr on the same line names it), since the bridge is a route a sandbox outside your network calls (see Deployment → Exposing webhooks without the admin API). With api.port: 0 the satellite binds nothing at all, which is the shape for a host that must accept no connection of any kind — at the price of no probe and no agent mode.

2. Pin the role

In the company config (Tier B), on the role that has to run there:

roles:
  - name: EU Support
    handle: eu-support
    goal: "Answer in-zone customer requests"
    placement:
      labels: {zone: eu}

labels requires every pair to be present and equal on the node. node: sat-eu-1 pins to one node id instead. Give both and both must hold — a placement only ever narrows.

Prefer a label over a node id. A label is a statement about what the host is (“this one is in the EU zone”), so a replacement host with the same label picks the seat up; a node id is a statement about which process, and it strands the seat when that particular process is gone.

3. Start it

On a stateless satellite there is one command:

crewlet run                     # roles come from the file

Its store is created fresh, at the binary’s own schema, every time it starts, so there is nothing to migrate — crewlet migrate refuses a scratch store and says so, and so do the offline config, secrets and search eval commands, because anything they wrote into it would be gone at the next boot. Configure the company through the API of a node that holds data.

A satellite that holds data is migrated on the satellite first:

crewlet migrate                 # this host's own store file
crewlet run

crewlet migrate is per node, not per fleet. There is no shared database to migrate from elsewhere: it applies the pending schema migrations to the one local store file its Tier A config names, and every node owns its file exclusively.

Or, if you would rather not put roles in the file:

crewlet run -roles seats

Verify it landed

The Settings › Nodes screen in the dashboard is the direct answer: it reads the lease table, so it gives the same picture from whichever node you happen to reach. Look for the satellite in Nodes with its roles and labels, and for the pinned handle in Seat ownership against that node.

From the logs on the satellite:

seat_claimed    seat=eu-support epoch=3
inbox_attached  seat=eu-support epoch=3 elapsed_ms=5.1

Probe it

A satellite with api.port set answers the same two probes every node does, so an orchestrator can restart one that wedged and wait for one to join before it replaces the next:

curl -s http://sat-eu-1.internal:8000/ready
# {"ready":true,"node":"sat-eu-1","configured":true,"draining":false,"posture":"serve"}

/health is liveness, and answers 200 for as long as the process is alive — through a drain, and through a broker link that is down — with the node’s half of the health envelope: its id, its roles, its posture and applied epoch, the seats it holds, and shutting_down.

/ready answers whether the node is doing its work, because a satellite takes no traffic for a probe to steer. It is 503 until all of these hold, naming the first that does not in reason:

`reason`	What it means here
`draining`	The node is stopping: its turns finish and it claims nothing new.
`broker_unlinked`	Its leaf link to every member is down (or, on an external cluster, its connection is reconnecting); `detail` says which. Its seats can neither receive nor publish anything.
`unconfigured`	No company revision has reached it yet.
`shed` or `stuck`	Its config posture: it cannot apply the revision its peers run.
`no_presence`	It does not hold its presence lease, so its peers do not count it and nothing routes to it.
`admission_withheld`	No data node has yet answered that a copy of the estate admits a seat — or the node cannot serve the seats it holds — so it claims nothing. This is the state a fresh satellite sits in until it is admitted, and the one it returns to while no data node is reachable.

Two failures to know by sight:

seats_unplaceable — no live node matches the selector, or the only one that does cannot serve its seats right now and has withdrawn (seats_shed_unserviceable on that node says why). Usually a typo (zone: EU does not match zone: eu; comparison is exact) or a satellite that has not started. The seat is not being served, and every other node’s sweep looks perfectly healthy, which is why this is logged rather than left to be noticed.
The label change did not take. Labels are advertised on the node’s presence lease, so a change takes effect one heartbeat after the restart that made it — editing the file is not enough.

What a satellite still needs

It is a full engine process with roles subtracted, so be honest about the dependency surface before choosing a host for it:

Outbound reach to the coordination slot and to the stream. Seat leases, the activation pointer, the ledgers and the seat’s inbox all live there. A network so restricted that neither is reachable cannot host a satellite. Its own store file is local, so that one costs nothing.
For a stateless satellite, a data node that answers. Its seats’ tracker and knowledge-base tools, their knowledge search and its tool-skill walks are each a request to a data node over the broker — no inbound port, the same link. It is admitted to claim seats only once a data node answers that its own copy is level with its logs, and while none answers its tools fail naming the estate nobody served rather than answering from nothing. What it publishes about its own turns is handed to a data node’s event log (the audit trail cannot live in a store deleted at its next boot), so GET /events on that data node shows it; its seats’ memory rides the compacted changelog every seat’s memory does and is rehydrated after a restart.
Whatever its LLM provider needs. Usually outbound HTTPS to the provider. A network with no egress at all can still work if the role uses a subscription CLI backend or an on-premises OpenAI-compatible endpoint.
The MCP servers its role declares, installed on that host — the whole reason the seat is there.
The same keyring, if company-config encryption is on. The satellite decrypts the company document and the secret store itself; without the keyring it cannot read the config at all.
Nothing inbound from the fleet or the outside world. No ingress rule, no public URL: the satellite dials out to the broker and coordination slot and is never dialled back. That is what makes this shape workable in a zone the rest of the fleet is not in. What reaches api.port is the orchestrator’s probes and, if a seat pinned here runs in agent mode, that seat’s box calling its /mcp/{token} bridge — the box must be able to dial this node for that one. api.port: 0 closes both.

What it costs

A pinned seat is unserved whenever nothing matches it. The engine will not widen a selector to keep a seat running — widening it is exactly what you asked it not to do. So when the satellite is down, that agent is down, and the fleet says so (seats_unplaceable) rather than quietly running it somewhere it does not belong. If that is not acceptable, run two satellites carrying the same label: the seat moves between them, and the fair share is computed per placement group, so the pinned seat does not eat into anything else’s capacity — and nothing else eats into the pinned seat’s: a satellite’s share of the unpinned seats is a separate bound from its share of its own, so it keeps room for the seat it exists for and claims it first. A seat whose teardown failed on the satellite is charged against the unpinned seats before the pinned one, for the same reason.

A satellite is eligible for unpinned seats too. It runs seats, so it takes its share of the ones nobody pinned — on top of its pinned seat, never instead of it — which is a real property to be deliberate about, because those seats’ MCP servers may not work in a restricted network. There is no “only take pinned seats” switch. To keep general work off it, pin the general work to the core, which is one label and a YAML anchor rather than a block per role:

roles:
  - name: CEO
    handle: ceo
    goal: "Set direction"
    placement: &core {labels: {tier: core}}       # anchor, on first use

  - {name: Engineer, handle: eng, goal: "Build", placement: *core}
  - {name: Designer, handle: design, goal: "Design", placement: *core}

  - name: EU Support
    handle: eu-support
    goal: "Answer in-zone customer requests"
    placement: {labels: {zone: eu}}

Give the core nodes labels: {tier: core} and the satellite only {zone: eu}, and each group stays on its own side. (The anchor has to be declared on a real placement field as above — a top-level holder key is rejected, since the company schema forbids unknown fields.)

Two more, inherited from running a fleet at all:

node.max_concurrent is per process, so the satellite has its own ceiling. Size it for one agent, not for the company — the default of 32 is sized for a node holding a company’s worth of seats, and a satellite running one seat wants a much smaller number.
A rolling upgrade across a lease-protocol bump makes new nodes wait for old ones. Upgrade the satellite in the same rollout as the core — see mixed-version fleets.

Sandboxed seats

A sandboxed seat can be pinned like any other, with three network facts the engine cannot check for you:

The satellite launches the sandbox, so it must reach the sandbox provider (E2B cloud, or your self-hosted domain).
Whichever node holds the sandbox-waiter duty polls it. On a satellite (roles: [seats]) that duty is on a core node by construction — so check that node’s reachability too, not just the satellite’s.
CREWLET_SANDBOX_OTEL_RECEIVER_URL must name an address the sandbox can reach, which means an ingress node. It is explicit config and is never derived from whichever node launched the run, so a satellite never advertises itself by accident.

Pinning a sandboxed seat to a node that cannot reach the provider gives you a seat that claims cleanly and fails every run. The engine knows what a node says it is, never what it can talk to.