# fleet-agent — on-host control-plane client (telemetry v1)

The workstation-side half of the fleet management plane. It dials the
**fleet-manager** agent plane, identifies with the host's **TPM**, and streams
health telemetry up. It is the client peer of the server hub in
`serving/fleet-manager/` (`agent.go` + `proto/fleet_agent.proto`).

Baked into the immutable verity image, so — like `fleet-hostapi` and `fleet-enrol`
— it is a **static, reproducible, `CGO_ENABLED=0`** Go binary built **out of the
build VM** by CI (deps proxy-fetched, `go.sum`-pinned) and file-provisioned in.

## What it does (v1 — telemetry only)

1. **Reuses the TPM identity for mTLS.** Loads the signing key at the persistent
   handle (`0x81000100`) as a `crypto.Signer` (`tpmkey.LoadSigner` — the private
   key never leaves the TPM) and the enrolment cert from NV (`0x01800100`), and
   presents them as the mTLS client cert. The manager verifies the chain to the
   fleet CA and derives the **cert serial = inventory key** — a host can only ever
   report as itself (`agent.go`: `peerSerial`).
2. **Opens the long-lived `Session` bidi stream** (host dials out; no inbound host
   port — works across the OPNsense L3 hop from the host VLAN to the mgmt plane).
3. **Sends `Hello`** (image version, kernel, kiosk URL, root hash, starship name —
   the fleet-generic facts, pulled from `fleet-hostapi` on `127.0.0.1:9099`).
4. **Sends a `HealthSnapshot` every `FLEET_AGENT_INTERVAL`** — load/cpu/temp/mem/
   tmpfs, nvme-root, 802.1X-macsec, selinux, chrony, kiosk-active — probed
   read-only from `/proc`+`/sys` (each probe degrades gracefully; a failure never
   kills the stream).
5. **Receives `DesiredState`/`Command` and LOGS them.** This build does **not**
   act on them. The reconcile actuators (apply kiosk URL, reboot, drain) are a
   deliberate follow-up (see `docs/TODO.md` #14) — the receive path is wired now so
   adding them needs no protocol change.

A dropped stream is retried with jittered backoff; the manager treats stream loss
as the host going **offline**.

## Prerequisite: the host must already be enrolled

The manager rejects the stream (`PermissionDenied`) until an inventory record
exists for the host's cert serial — that record is born when an admin **approves**
the host's TPM enrolment (`fleet-enrol` → enrol-broker → manager). Enrolment
precedes the agent; this ordering is expected.

## Config (`/etc/fleet-agent/agent.env`)

All values are **fleet-generic** (invariant #1). See the file for the full list:
`FLEET_AGENT_MANAGER` (manager `host:port`), `FLEET_AGENT_CA` (fleet root, reused
from `/etc/dot1x/radius-ca.pem`), `FLEET_AGENT_HANDLE` / `FLEET_AGENT_NVINDEX` (TPM
identity, mirror `rd.dot1x.*`), `FLEET_AGENT_INTERVAL`, `FLEET_AGENT_HOSTAPI`.

## Layout

| file | purpose |
|------|---------|
| `main.go` | config, connect loop (jittered backoff), `Session` send/recv |
| `identity.go` | TPM-backed mTLS client cert + fleet-CA-verifying `tls.Config` |
| `snapshot.go` | read-only `/proc`+`/sys` health probes + hostapi facts fetch |
| `tpmkey/` | **copy** of `files/enrol/tpmkey` + read-only `LoadSigner` (see its header) |
| `proto/` | **copy** of the generated `fleet.agent.v1` package (one `.proto` contract, two peers) |
| `fleet-agent.service` | hardened unit (tss group for the TPM, INET egress) |

## Build / test

```bash
cd files/agent
CGO_ENABLED=0 go build -trimpath -buildvcs=false -ldflags '-s -w -buildid=' -o bin/fleet-agent .
go test ./...
# TPM handshake end-to-end (go-tpm software simulator, CGO — isolated module):
( cd simtest && CGO_ENABLED=1 go test ./... )
```