mcp-ssh-fleet

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MCP server that gives an agent two tools over SSH to a fleet of hosts outside Kubernetes. The SSH key is a mounted secret (never enters model context); the inventory is a fail-closed allowlist.

Tools

• ssh_probe(tags, check) — curated read-only diagnostics on every host carrying the given tags (AND semantics, like GitLab runner tags). check is one of a built-in set: uptime, disk, mem, failed, logs. Arbitrary commands cannot be passed. Class: read-only.
• ssh_exec(host, command) — one arbitrary non-interactive command on ONE inventory host (by name or address; hosts outside the inventory are refused). Class: write-external: the server executes the command, while access gating (approval/RBAC) belongs to the MCP client.

Both: output size cap, per-host timeout, TOFU host-key check (fingerprint in logs), output as one section per host.

Configuration (env)

Variable	Default	Meaning
SSH_FLEET_TRANSPORT	http	http (StreamableHTTP, endpoint /mcp) | sse | stdio
SSH_FLEET_ADDR	:8080	listen address for http/sse
SSH_FLEET_AUTH_TOKEN	—	optional X-MCP-AUTH token
SSH_FLEET_INVENTORY_PATH	/etc/ssh-fleet/inventory.yaml	path to the inventory (configmap)
SSH_FLEET_KEY_PATH	/etc/ssh-fleet/id_ed25519	path to the private key (secret)
SSH_FLEET_OUTPUT_CAP_BYTES	8192	output cap per section
SSH_FLEET_CMD_TIMEOUT_SECONDS	20	per-host timeout
SSH_FLEET_PROBE_CONCURRENCY	8	probe parallelism pool
SSH_FLEET_PROBE_MAX_HOSTS	50	safety cap on hosts per probe

Inventory format — see deploy/inventory.example.yaml.

Quickstart (docker, stdio)

docker run -i --rm \
  -v /path/to/inventory.yaml:/etc/ssh-fleet/inventory.yaml:ro \
  -v /path/to/id_ed25519:/etc/ssh-fleet/id_ed25519:ro \
  -e SSH_FLEET_TRANSPORT=stdio \
  ghcr.io/inhuman/mcp-ssh-fleet:latest

This is the shape MCP clients use when installing from the MCP Registry (io.github.inhuman/mcp-ssh-fleet).

Connecting an MCP client (http/sse)

By default the server speaks StreamableHTTP; register it as a regular HTTP MCP server with endpoint /mcp (URL like http://<host>:8080/mcp). Both tools become available to the client.

Client-side security recommendations:

• ssh_probe is read-only (curated checks only) and can be granted broadly.
• ssh_exec is arbitrary execution (write-external). Gate its access on the client side (approval / RBAC / user allowlist) — the server merely executes a command on an inventory host; it does not decide access policy.

Development

make test        # unit tests + e2e against a real in-process SSH server
make vet
make vulncheck
make build
make docker

Release: tag vX.Y.Z → GitHub Actions builds and publishes a multi-arch image to ghcr.io/inhuman/mcp-ssh-fleet.