10 -- Discovery: Docker

Prerequisite: 01 -- HTTP GatewayYou will need: Running Hangar, Docker or Podman Time: 10 minutes Adds: Auto-discover MCP providers from Docker container labels

The Problem

You have MCP providers running as Docker containers. You don't want to manually update config.yaml every time a container starts or stops. You want Hangar to detect them automatically.

The Config

# config.yaml -- Recipe 10: Docker Discovery
discovery:                               # NEW: discovery configuration
  enabled: true                          # NEW: enable auto-discovery
  refresh_interval_s: 30                 # NEW: scan every 30 seconds
  auto_register: false                   # NEW: require manual approval

  sources:                               # NEW: discovery sources
    - type: docker                       # NEW: Docker source
      mode: additive                     # NEW: only add, never remove

Try It

1. Start an MCP provider container with labels:

   docker run -d --name my-provider \
     -l mcp.hangar.enabled=true \
     -l mcp.hangar.name=docker-math \
     -l mcp.hangar.mode=http \
     -l mcp.hangar.port=8080 \
     my-mcp-server:latest

2. Start Hangar:

   mcp-hangar serve --http --port 8000

3. Trigger a discovery scan:

   curl -X POST http://localhost:8000/api/discovery/sources

4. Check pending providers:

   curl http://localhost:8000/api/discovery/pending

   {"pending": [{"name": "docker-math", "source": "docker", "mode": "remote"}]}

5. Approve the provider:

   curl -X POST http://localhost:8000/api/discovery/approve/docker-math

6. Verify it's registered:

   mcp-hangar status

   docker-math    remote    cold    source=docker:auto-discovery

What Just Happened

The Docker discovery source connects to the Docker socket and lists containers with mcp.hangar.enabled=true labels. In additive mode, it only adds new providers -- never removes existing ones. With auto_register: false, discovered providers go to a pending queue for manual approval.

Set auto_register: true if you trust all labeled containers and want zero-touch registration.

Key Config Reference

Key	Type	Default	Description
discovery.enabled	bool	false	Enable auto-discovery
discovery.refresh_interval_s	int	30	Seconds between scans
discovery.auto_register	bool	false	Register without approval
discovery.sources[].type	string	--	docker, filesystem, kubernetes, entrypoint
discovery.sources[].mode	string	--	additive (add only) or authoritative (add and remove)

Docker Labels

Label	Required	Default	Description
mcp.hangar.enabled	Yes	--	Must be "true"
mcp.hangar.name	No	Container name	Provider name
mcp.hangar.mode	No	http	Provider mode
mcp.hangar.port	No	8080	Provider port
mcp.hangar.group	No	--	Auto-add to group

What's Next

Docker discovery works for local and CI environments. For Kubernetes, you need annotation-based discovery.

--> 11 -- Discovery: Kubernetes