Networking

The generated Compose service publishes MCP on host loopback by default:

http://127.0.0.1:8025/mcp

The service listens on all container interfaces so Docker's host-loopback port publish can reach it. The host publish remains loopback-only unless you change AGENT_ARBITER_HOST_BIND.

Docker env values

Edit Docker wrapper settings with:

./arbiter-docker/arbiter-docker edit-docker

Common values in docker.env:

• AGENT_ARBITER_HOST_BIND: host bind address, default 127.0.0.1.
• AGENT_ARBITER_HOST_PORT: host port, default 8025.
• AGENT_ARBITER_CONTAINER_PORT: container port, default 8025.
• AGENT_ARBITER_DOCKER_NETWORK_NAME: Docker network name, default agent-arbiter.
• AGENT_ARBITER_DOCKER_BRIDGE_NAME: bridge interface name, default agent-arbiter0.
• AGENT_ARBITER_DOCKER_SUBNET: bridge subnet, default 172.31.250.0/24.

Bridge overrides

The standard Compose file uses a deterministic Docker bridge so firewall rules can target stable names:

• Docker network name: agent-arbiter
• bridge interface: agent-arbiter0
• bridge subnet: 172.31.250.0/24

If that subnet or interface name conflicts with the host, override them for the Compose invocation. Keep the bridge interface name short enough for Linux network interface limits:

cd /opt/arbiter
AGENT_ARBITER_DOCKER_BRIDGE_NAME=arbiter1 \
AGENT_ARBITER_DOCKER_SUBNET=172.31.251.0/24 \
sudo --preserve-env=AGENT_ARBITER_DOCKER_BRIDGE_NAME,AGENT_ARBITER_DOCKER_SUBNET \
  docker compose --env-file /opt/arbiter/docker.env \
  -f /opt/arbiter/compose.yaml up -d

The helper normally wraps docker compose for you. Use the manual form only when you need one-off Docker options that the helper does not expose.

Exposure

Keep the host bind on 127.0.0.1 unless the deployment is intentionally exposed through a controlled local proxy or firewall rule. The host file permissions protect deployment state and secrets; they do not add authentication to the MCP API. Any local process that can reach the MCP endpoint can use the tools allowed by the configured policy.