MCPServer CRD

The MCPServer custom resource deploys MCP (Model Context Protocol) tool servers that agents can use.

Full Specification

apiVersion: kaos.tools/v1alpha1
kind: MCPServer
metadata:
  name: my-mcp
  namespace: my-namespace
spec:
  # Required: Runtime identifier
  # Use a registered runtime (python-string, kubernetes, slack) or "custom"
  runtime: python-string
  
  # Optional: Runtime-specific parameters
  # Passed to container via runtime's paramsEnvVar (e.g., MCP_TOOLS_STRING for python-string)
  params: |
    def echo(text: str) -> str:
        """Echo the input text."""
        return f"Echo: {text}"
  
  # Optional: ServiceAccount for RBAC (e.g., kubernetes runtime)
  serviceAccountName: my-mcp-sa
  
  # Optional: Container overrides
  container:
    image: my-custom-image:v1  # Required for "custom" runtime
    env:
    - name: LOG_LEVEL
      value: "INFO"
    resources:
      requests:
        memory: "128Mi"
        cpu: "100m"
  
  # Optional: Full PodSpec override
  podSpec:
    nodeSelector:
      gpu: "true"

status:
  phase: Ready           # Pending, Ready, Failed
  ready: true
  endpoint: "http://mcpserver-my-mcp.my-namespace.svc.cluster.local:8000"
  availableTools:
  - "echo"
  message: ""

Spec Fields

runtime (required)

Runtime identifier for the MCP server. Can be:

Value	Description
python-string	Python code execution via MCP_TOOLS_STRING
kubernetes	Kubernetes CRUD operations
slack	Slack integration
custom	User-provided container image

Additional runtimes can be registered via the kaos-mcp-runtimes ConfigMap.

params (optional)

Runtime-specific configuration passed to the container. The delivery method depends on the runtime:

Runtime	Params Environment Variable
python-string	MCP_TOOLS_STRING
kubernetes	MCP_PARAMS
slack	MCP_PARAMS

python-string params

For the python-string runtime, define Python functions inline:

spec:
  runtime: python-string
  params: |
    def greet(name: str) -> str:
        """Greet a person by name."""
        return f"Hello, {name}!"
    
    def calculate(expression: str) -> str:
        """Evaluate a math expression."""
        try:
            return str(eval(expression))
        except Exception as e:
            return f"Error: {e}"

Requirements:

• Functions must have type annotations
• Functions must have docstrings (used as descriptions)
• Supported types: str, int, dict, list

Security Note: python-string uses exec() to define functions. Only use with trusted input.

serviceAccountName (optional)

ServiceAccount for the MCPServer pod. Required for runtimes that need Kubernetes API access (e.g., kubernetes runtime).

Create RBAC using:

kaos system create-rbac --name my-mcp-sa --namespace my-namespace

container (optional)

Override container configuration. For "custom" runtime, container.image is required.

spec:
  runtime: custom
  container:
    image: my-mcp-server:v1
    env:
    - name: API_KEY
      valueFrom:
        secretKeyRef:
          name: mcp-secrets
          key: api-key
    resources:
      requests:
        memory: "256Mi"
        cpu: "100m"

podSpec (optional)

Override the generated pod spec using Kubernetes strategic merge patch.

gatewayRoute (optional)

Configure Gateway API routing, including request timeout:

spec:
  gatewayRoute:
    timeout: "30s"  # Default for MCPServer

Available Runtimes

python-string

Execute Python functions defined in params.

spec:
  runtime: python-string
  params: |
    def echo(message: str) -> str:
        """Echo back the message."""
        return f"Echo: {message}"

kubernetes

Kubernetes CRUD operations. Requires serviceAccountName with appropriate RBAC.

spec:
  runtime: kubernetes
  serviceAccountName: k8s-mcp-sa

slack

Slack integration. Configure via container environment variables.

spec:
  runtime: slack
  container:
    env:
    - name: SLACK_BOT_TOKEN
      valueFrom:
        secretKeyRef:
          name: slack-secrets
          key: bot-token

custom

User-provided MCP server image. Must expose HTTP on port 8000.

spec:
  runtime: custom
  container:
    image: my-mcp-server:v1

Status Fields

Field	Type	Description
phase	string	Current phase: Pending, Ready, Failed
ready	bool	Whether server is ready
endpoint	string	Service URL for agents
availableTools	[]string	List of tool names
message	string	Additional status info
deployment	object	Deployment status

Examples

Echo Tool (python-string)

apiVersion: kaos.tools/v1alpha1
kind: MCPServer
metadata:
  name: echo-tools
spec:
  runtime: python-string
  params: |
    def echo(message: str) -> str:
        """Echo the message back."""
        return f"Echo: {message}"

Calculator (python-string)

apiVersion: kaos.tools/v1alpha1
kind: MCPServer
metadata:
  name: calculator
spec:
  runtime: python-string
  params: |
    def add(a: int, b: int) -> int:
        """Add two numbers together."""
        return a + b
    
    def subtract(a: int, b: int) -> int:
        """Subtract b from a."""
        return a - b

Kubernetes CRUD

apiVersion: kaos.tools/v1alpha1
kind: MCPServer
metadata:
  name: k8s-tools
spec:
  runtime: kubernetes
  serviceAccountName: k8s-mcp-sa

Custom MCP Server

apiVersion: kaos.tools/v1alpha1
kind: MCPServer
metadata:
  name: my-custom
spec:
  runtime: custom
  container:
    image: ghcr.io/myorg/my-mcp-server:v1
    env:
    - name: API_KEY
      valueFrom:
        secretKeyRef:
          name: api-secrets
          key: key

Integration with Agent

Reference MCPServer in Agent spec:

apiVersion: kaos.tools/v1alpha1
kind: Agent
metadata:
  name: my-agent
spec:
  modelAPI: my-modelapi
  model: gpt-4
  mcpServers:
  - echo-tools
  - calculator
  config:
    instructions: |
      You have access to echo and calculator tools.

CLI Commands

# List MCPServers
kaos mcp list

# Deploy from YAML
kaos mcp deploy mcpserver.yaml

# Deploy custom image directly
kaos mcp deploy --name my-mcp --image my-image:v1

# Deploy registered runtime
kaos mcp deploy --name my-mcp --runtime slack

# Get details
kaos mcp get my-mcp

# View logs
kaos mcp logs my-mcp

# Invoke a tool
kaos mcp invoke my-mcp --tool echo --args '{"message": "hello"}'

# Delete
kaos mcp delete my-mcp

Creating Custom MCP Servers

Use the CLI to scaffold and build custom MCP servers:

# Initialize project
kaos mcp init my-server

# Edit server.py with your tools

# Build image
kaos mcp build --name my-server --tag v1

# Load to KIND (for local testing)
kaos mcp build --name my-server --tag v1 --kind-load

# Deploy
kaos mcp deploy --name my-server --image my-server:v1

Troubleshooting

MCPServer CrashLoopBackOff

Check pod logs:

kaos mcp logs my-mcp

Common causes:

• Invalid Python syntax in params
• Missing serviceAccountName for kubernetes runtime
• Image pull errors for custom runtime

Tools Not Discovered

Verify MCPServer is Ready:

kaos mcp get my-mcp

RBAC Errors (kubernetes runtime)

Create appropriate permissions:

kaos system create-rbac --name my-mcp-sa --namespace my-ns
kubectl apply -f rbac.yaml