ButterStack Connector

An outbound-only daemon a game studio runs inside its own network so ButterStack can reach a private, on-premises Perforce, TeamCity, Jenkins, GitHub Enterprise Server, or Horde without the studio opening a single inbound port. One outbound TLS connection to one hostname on 443. A typed command allowlist, never a tunnel and never a shell. Credentials stay on the studio's disk and never cross the wire.

Status: pre-release. Tracking: ButterStack/butter_stack#1575.

What it is

The connector is a daemon the studio runs on its own hardware (or in a container on its own network). It opens exactly one outbound TLS connection to wss://connect.butterstack.com/connect on port 443, announces what it can do, and then executes only commands from a typed, versioned allowlist with constrained arguments, each one logged locally. Every credential the studio configures (Perforce tickets, TeamCity tokens) stays in the studio's config file and never crosses the wire. There is no inbound port, no tunnel, no shell, and no remote configuration: the broker cannot tell the connector where to find a credential.

Requirements

• Go 1.25 or later (for building from source)
• Ruby 3.2+ (only for running the drill harness in test/)
• A ButterStack account with a connector token issued from the project's Connectors UI

Install

From source:

go build -o butterstack-connector ./cmd/butterstack-connector

Docker image (from the in-tree Dockerfile):

docker build -t butterstack-connector .

The Dockerfile produces a minimal image with a static Go binary and a Ruby runtime for the UAT entrypoint. In production, the entrypoint runs the connector directly from /usr/local/bin/butterstack-connector.

Configure

Copy connector.example.yml to your install location (e.g. /etc/butterstack/connector.yml) and set its permissions to 0600. The daemon refuses to start if the config file or any *_file path is readable by group or other users.

install -m 0600 connector.example.yml /etc/butterstack/connector.yml

Every credential comes from this file, or from a *_file path it names. There is no environment-variable fallback, no flag that takes a secret, and no remote configuration.

Fields

Field	Type	Secret	Source	Description
endpoint	string	no	file	The broker URL. Must be wss:// with no query string, no userinfo, no fragment. This is the one hostname your egress rule needs.
endpoint_ca_file	string	no	file	Optional. Pins the trust anchor for the endpoint, for a private CA or a TLS-inspecting proxy. There is no option to skip verification for the broker connection.
token	string	yes	file	The connector token issued in the ButterStack UI. Shown exactly once at issue time. Format: bsc_<project-id>_<secret>.
token_file	string	no	file	Alternative to token: path to a file containing the token (for vault-injected secrets). Mutually exclusive with token. The file must be mode 0600.
connector_id	string	no	file	A name for this host, shown in the Connection Status panel.
log_dir	string	no	file	Local audit log directory. One JSON line per command, including every denial. Defaults to a logs/ directory next to the config file.
max_concurrent	int	no	file	Commands executed in parallel. Range: 1-32. Default: 4.
scopes.depot_scope	list	no	file	Literal Perforce depot prefixes (no wildcards). A path whose literal prefix is not inside one of these is denied.
scopes.allowed_build_types	list	no	file	For the reserved teamcity.build.queue verb. Not compiled in v0.
scopes.repo_allowlist	list	no	file	For the reserved ghes.* verbs. Not compiled in v0.
toggles.content_verbs	bool	no	file	Content-class verbs are off in v0 at the schema level. This switch cannot turn one on yet.
perforce.enabled	bool	no	file	Enable the Perforce tool.
perforce.binary	string	no	file	Path to the p4 CLI. Default: p4.
perforce.port	string	no	file	Helix Core server address (e.g. ssl:perforce.studio.lan:1666).
perforce.user	string	no	file	A read-only Perforce user.
perforce.ticket	string	yes	file	The Perforce ticket. Passed to p4 via the P4PASSWD environment variable so it does not appear in the process list.
perforce.ticket_file	string	no	file	Alternative to perforce.ticket. Must be mode 0600.
perforce.timeout	duration	no	file	Timeout for p4 commands. Default: 20s.
teamcity.enabled	bool	no	file	Enable the TeamCity tool.
teamcity.url	string	no	file	The TeamCity server URL on your LAN (e.g. https://teamcity.studio.lan).
teamcity.token	string	yes	file	A project-limited TeamCity access token with a read-only role. Never crosses the wire.
teamcity.token_file	string	no	file	Alternative to teamcity.token. Must be mode 0600.
teamcity.ca_file	string	no	file	Optional. Trust anchor for a self-signed certificate on your LAN TeamCity. Scoped to this server only, not the broker connection.
teamcity.allow_insecure_tls	bool	no	file	Skip TLS verification for the LAN TeamCity. There is no equivalent for the broker connection, which always verifies.
teamcity.timeout	duration	no	file	Timeout for TeamCity REST calls. Default: 10s.

Two rules the daemon enforces at startup rather than documents:

• connector.yml and every *_file must be mode 0600 or stricter, or it refuses to start.
• The endpoint must be wss:// with no query string. A copy-pasted ?token=... URL cannot start the daemon at all.

Run

Foreground:

./butterstack-connector -config /etc/butterstack/connector.yml

Print the compiled vocabulary:

./butterstack-connector -print-vocabulary

systemd unit (example):

[Unit]
Description=ButterStack Connector
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
User=butterstack-connector
ExecStart=/usr/local/bin/butterstack-connector -config /etc/butterstack/connector.yml
Restart=on-failure
RestartSec=5s

[Install]
WantedBy=multi-user.target

Docker Compose (example):

services:
  connector:
    image: butterstack-connector
    build: .
    entrypoint:
      - /usr/local/bin/butterstack-connector
      - -config
      - /etc/butterstack/connector.yml
    volumes:
      - ./connector.yml:/etc/butterstack/connector.yml:ro
    restart: unless-stopped

Verify

The drill harness (test/drills.rb) runs seven drills from design note section 4.3 against the mock broker (test/mock_broker.rb), plus a round-trip phase and the broker-side half of drill (f). Requires Ruby 3.2+ and a built binary.

make check        # go vet + go test + drills
make test         # go vet + go test only
make drills       # drills only (needs a built binary)
make build        # build the binary
make vocabulary   # print the compiled allowlist

make build uses docker run golang:1.23-alpine by default. If you have Go on the host, GO=go make build uses it directly.

See test/README.md for details on the individual drills and the mock broker.

Supported backends

Backend	Status	Compiled verbs
Perforce (Helix Core)	Implemented	p4.describe, p4.changes
TeamCity	Implemented	teamcity.server.info, teamcity.build.get
Jenkins	Planned (reserved)	jenkins.build.trigger (denied in v0)
GitHub Enterprise Server	Planned (reserved)	ghes.commit.get (denied in v0)
Horde	Planned (reserved)	horde.server.info (denied in v0)

System verbs (sys.ping, sys.version, sys.capabilities) are always compiled and touch no studio tool.

Reserved verbs are listed in the vocabulary so that the schema is self-documenting and the drills exercise their denial path, but they cannot be executed in this build. p4.file_contents is reserved as a content-class verb and is off at both the schema level and the config level. teamcity.build.queue is reserved as a mutation-class verb. No mutating verb and no content-class verb is compiled in v0.

See internal/vocab/vocab.go for the full allowlist.

Protocol

See PROTOCOL.md for the wire-level protocol details: transport, authentication, frame format, vocabulary resolution, and the audit log.