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Tailscale

Read when:

  • adding or debugging tailnet reachability for a lease;
  • deciding whether a host is provider-owned or only network-reachable;
  • changing SSH, VNC, or coordinator bootstrap behavior over a tailnet.

Tailscale is an optional reachability layer, not a provider. Providers still own the machines (Hetzner, AWS, Azure, Google Cloud, Proxmox, static SSH hosts, and the rest). Tailscale only changes which host Crabbox dials when it runs SSH-backed work against a lease.

Scope

  • Managed Linux leases can join a tailnet at creation time with --tailscale. Tailscale provisioning is offered by the providers that declare the capability: Hetzner, AWS, Azure, and Google Cloud.
  • Static (provider=ssh) hosts are not joined by Crabbox; point static.host at a MagicDNS name or 100.x address and assert reachability with --network tailscale.
  • --tailscale is rejected for non-Linux targets, for Blacksmith Testbox (Blacksmith owns connectivity), for static hosts, and for sandbox providers such as Sprites that expose SSH through their own proxy.

Commands

Create a managed Linux lease that joins the configured tailnet:

crabbox warmup --tailscale
crabbox run --tailscale -- pnpm test
crabbox run --tailscale --desktop --browser -- pnpm test:e2e

Choose the connection path when acting on an existing lease (ssh, vnc, screenshot, webvnc, status, inspect, and reused run --id leases):

crabbox ssh --id swift-crab --network auto
crabbox ssh --id swift-crab --network tailscale
crabbox vnc --id swift-crab --network tailscale --open
crabbox run --id swift-crab --network public -- pnpm test

Network modes

--network (config key network, default auto) selects how the SSH endpoint is resolved:

  • auto: prefer the tailnet host when the lease carries Tailscale metadata and SSH is reachable there; otherwise fall back to the provider/public host.
  • tailscale: require a tailnet host and fail clearly when this client cannot reach it over SSH.
  • public: force the provider/public host (useful for debugging).

When auto falls back to the public host, Crabbox prints network fallback tailscale_unreachable and reports the selected path in ready/status output (ready ssh=… network=public …) instead of silently switching.

Config

network: auto
tailscale:
  enabled: true
  tags:
    - tag:crabbox
  hostnameTemplate: crabbox-{slug}
  authKeyEnv: CRABBOX_TAILSCALE_AUTH_KEY
  exitNode: build-host.example.ts.net
  exitNodeAllowLanAccess: true

tailscale.enabled (or --tailscale) requests a tailnet join for newly created managed Linux leases. tailscale.network is an alias that sets the top-level network mode used for target resolution on SSH-backed commands. Hostname templates support {id}, {slug}, and {provider}; the rendered value is sanitized to a DNS label. When enabled is set, tags must contain at least one valid tag: value and hostnameTemplate must be non-empty.

Environment overrides:

CRABBOX_TAILSCALE=1
CRABBOX_NETWORK=auto|tailscale|public
CRABBOX_TAILSCALE_TAGS=tag:crabbox,tag:ci
CRABBOX_TAILSCALE_HOSTNAME_TEMPLATE=crabbox-{slug}
CRABBOX_TAILSCALE_AUTH_KEY_ENV=CRABBOX_TAILSCALE_AUTH_KEY
CRABBOX_TAILSCALE_AUTH_KEY=<direct-provider only>
CRABBOX_TAILSCALE_EXIT_NODE=build-host.example.ts.net
CRABBOX_TAILSCALE_EXIT_NODE_ALLOW_LAN_ACCESS=1

Flag equivalents: --tailscale, --network, --tailscale-tags, --tailscale-hostname-template, --tailscale-auth-key-env, --tailscale-exit-node, and --tailscale-exit-node-allow-lan-access.

In direct-provider mode the auth key is read from the variable named by tailscale.authKeyEnv (default CRABBOX_TAILSCALE_AUTH_KEY). Managed VM providers normally use a one-off key. Islo requires a reusable, ephemeral key because its snapshot-safe memory-only node identity must re-enroll after daemon loss. Brokered mode does not need a local key; the coordinator mints one per lease (see below).

Exit nodes

Exit-node egress is opt-in per lease. The lease routes its outbound internet through an approved tailnet exit node after it joins Tailscale:

crabbox warmup --tailscale --tailscale-exit-node build-host.example.ts.net --tailscale-exit-node-allow-lan-access
crabbox run --tailscale --tailscale-exit-node 100.100.100.100 -- curl -4 https://ifconfig.me

exitNodeAllowLanAccess maps to Tailscale's LAN-access flag and requires exitNode. The exit node must already advertise exit-node capability and be approved in the Tailscale admin console, and the tailnet policy must grant the lease's tags (for example tag:crabbox) access to autogroup:internet through exit nodes.

When an exit node is selected, network: auto prefers the tailnet host for bootstrap because the provider/public SSH path can become asymmetric once the lease routes outbound traffic through the exit node. Before sync or the remote command, Crabbox verifies on the box that an exit node is selected in tailscale prefs and that the node can reach the public internet. If that check fails, the run stops and reports the exit-node egress failure (tailscale exit node … joined but remote internet egress failed), which usually means the exit node is not approved, the policy does not grant autogroup:internet to the lease tag, or the exit-node machine is not forwarding.

Brokered mode

When a lease is created through the coordinator, it mints a fresh auth key per lease using Tailscale OAuth. Secrets live in coordinator configuration:

CRABBOX_TAILSCALE_CLIENT_ID
CRABBOX_TAILSCALE_CLIENT_SECRET
CRABBOX_TAILSCALE_TAILNET    optional, defaults to "-"
CRABBOX_TAILSCALE_TAGS       default/allowed comma-separated tags (default tag:crabbox)
CRABBOX_TAILSCALE_ENABLED    set 0 to force-disable, 1 to force-enable
CRABBOX_TAILSCALE_INSTALL_MODE package or pinned (default package)
CRABBOX_TAILSCALE_VERSION       pinned static build version
CRABBOX_TAILSCALE_SHA256_AMD64  pinned amd64 archive checksum
CRABBOX_TAILSCALE_SHA256_ARM64  pinned arm64 archive checksum

The OAuth client's tags and each requested lease tag must also satisfy Tailscale's ownership rules:

  • Single tag: give the OAuth client tag:crabbox and set CRABBOX_TAILSCALE_TAGS=tag:crabbox. The tag sets match exactly.
  • Multi-tag exact match: an OAuth client with tag:ci,tag:staging can mint a key requesting both tags together without extra ownership rules.
  • Multi-tag subsets: requesting only tag:ci from that two-tag client requires tag:ci to own itself in tagOwners; do the same for every subset tag.
  • Deployment-owner pattern: preferably give the OAuth client one narrow owner tag, such as tag:crabbox-deployer, and make that tag an owner of each workload tag that Crabbox may request.

Example deployment-owner policy:

{
  "tagOwners": {
    "tag:crabbox-deployer": ["autogroup:admin"],
    "tag:ci": ["tag:crabbox-deployer"],
    "tag:staging": ["tag:crabbox-deployer"]
  }
}

Then assign only tag:crabbox-deployer to the OAuth client and set CRABBOX_TAILSCALE_TAGS=tag:ci,tag:staging. This keeps the client least-privilege without requiring it to carry every workload tag. Do not broaden the OAuth client to unrelated tags just to resolve an ownership error.

Flow:

  1. The CLI sends the requested Tailscale settings (enabled, tags, hostname, optional exit node) in CreateLease.
  2. The coordinator validates the requested tags against CRABBOX_TAILSCALE_TAGS and rejects any tag outside that set.
  3. The coordinator exchanges the OAuth client for a token and mints a one-off auth key that is non-reusable, ephemeral, pre-approved, tagged, and expires in 10 minutes.
  4. The key is injected only into the runner's cloud-init user-data.
  5. The runner installs Tailscale, runs tailscale up with the requested hostname and tags, and writes non-secret metadata under /var/lib/crabbox (tailscale-ipv4, -hostname, -fqdn, -version, -device-id, and exit-node markers).
  6. After SSH readiness, the CLI reads that metadata and posts it back to the coordinator so the lease record carries the tailnet address.

The auth key is never stored in lease records, provider labels, run logs, or local config. The short-lived key can still appear in user-data at the provider, so the Worker only mints one-off ephemeral keys — never long-lived reusable keys.

The default package mode configures Tailscale's signed stable APT repository, verifies and scopes its pinned keyring with signed-by, installs the current package, and records the client version. Set CRABBOX_TAILSCALE_INSTALL_MODE=pinned to download a static archive, verify the configured SHA-256 checksum, and install the tailscale and tailscaled binaries. Neither mode pipes a downloaded installer script into a root shell.

On release, crabbox stop attempts a best-effort remote tailscale logout before provider cleanup when SSH is still reachable. Coordinator cleanup does not delete a device by an ID posted from the lease client; that metadata is diagnostic, not trusted authorization for a privileged tailnet operation. One-off nodes are ephemeral and age out in Tailscale if remote logout is unavailable.

If Tailscale rejects a requested subset or unowned tag, the coordinator returns invalid_tailscale_tags with exact-match/tagOwners guidance and preserves the raw Tailscale HTTP status and response body for diagnosis.

Preflight the coordinator without leasing a machine:

CRABBOX_TAILSCALE_ENABLED=0 scripts/live-tailscale-smoke.sh --json
CRABBOX_LIVE=1 CRABBOX_COORDINATOR=https://broker.example.com CRABBOX_ADMIN_TOKEN=replace-me scripts/live-tailscale-smoke.sh --json

SSH and VNC

Crabbox continues to use OpenSSH with per-lease keys; Tailscale SSH is not used. Tailscale only changes the SSH endpoint from the public/provider host to the tailnet host.

Managed VNC remains loopback-bound and tunneled over SSH:

local localhost:5901 -> SSH -> remote 127.0.0.1:5900

Crabbox does not bind managed VNC to 100.x addresses and does not use Tailscale Serve, Funnel, or noVNC for managed leases.

Static hosts

Static hosts are operator-managed. Point static.host at a MagicDNS name or 100.x address and use --network tailscale to assert reachability:

provider: ssh
target: macos
static:
  host: build-host.example.ts.net
  user: alice
  port: "22"
  workRoot: /Users/alice/crabbox

For static hosts, --network tailscale only asserts reachability and probes SSH; Crabbox does not install or join Tailscale on the host.

Tailscale references

Related docs