Service Registration

Servicekit provides automatic service registration with an orchestrator for service discovery in Docker Compose and Kubernetes environments.

Quick Start

Basic Registration

The simplest approach with auto-detected hostname:

from servicekit.api import BaseServiceBuilder, ServiceInfo

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="My Service"))
    .with_registration()  # Reads SERVICEKIT_ORCHESTRATOR_URL from environment
    .build()
)

Set the environment variable:

export SERVICEKIT_ORCHESTRATOR_URL=http://orchestrator:9000/services/$register
fastapi run your_file.py

Docker Compose

The recommended approach for multi-service deployments:

services:
  orchestrator:
    image: your-orchestrator:latest
    ports:
      - "9000:9000"

  my-service:
    image: your-service:latest
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register
      # Hostname auto-detected from container name
    depends_on:
      - orchestrator

Custom ServiceInfo

For services with additional metadata:

from servicekit.api import ServiceInfo

class CustomServiceInfo(ServiceInfo):
    """Extended service info with custom fields."""
    deployment_env: str = "production"
    team: str = "platform"
    capabilities: list[str] = []

app = (
    BaseServiceBuilder(
        info=CustomServiceInfo(
            display_name="My Service",
            version="1.0.0",
            deployment_env="staging",
            team="data-science",
            capabilities=["ml-inference", "analytics"],
        )
    )
    .with_registration()
    .build()
)

---

Configuration Options

The .with_registration() method accepts these parameters:

.with_registration(
    orchestrator_url=None,              # Direct value or env var
    host=None,                          # Direct value, auto-detect, or env var
    port=None,                          # Direct value, env var, or 8000
    orchestrator_url_env="SERVICEKIT_ORCHESTRATOR_URL",
    host_env="SERVICEKIT_HOST",
    port_env="SERVICEKIT_PORT",
    max_retries=5,                      # Number of registration attempts
    retry_delay=2.0,                    # Seconds between retries
    fail_on_error=False,                # Abort startup on failure
    timeout=10.0,                       # HTTP request timeout
)

Parameters

• orchestrator_url (str | None): Orchestrator registration endpoint URL. If None, reads from environment variable.
• host (str | None): Service hostname. If None, auto-detects via socket.gethostname() or reads from environment variable.
• port (int | None): Service port. If None, reads from environment variable or defaults to 8000.
• orchestrator_url_env (str): Environment variable name for orchestrator URL. Default: SERVICEKIT_ORCHESTRATOR_URL.
• host_env (str): Environment variable name for hostname override. Default: SERVICEKIT_HOST.
• port_env (str): Environment variable name for port override. Default: SERVICEKIT_PORT.
• max_retries (int): Maximum number of registration attempts. Default: 5.
• retry_delay (float): Delay in seconds between retry attempts. Default: 2.0.
• fail_on_error (bool): If True, raise exception and abort startup on registration failure. If False, log warning and continue. Default: False.
• timeout (float): HTTP request timeout in seconds. Default: 10.0.

---

How It Works

Registration Flow

1. Service Starts: FastAPI application initializes during lifespan startup
2. Hostname Resolution: Determines service hostname (see resolution order below)
3. Port Resolution: Determines service port (see resolution order below)
4. URL Construction: Builds service URL as http://<hostname>:<port>
5. Payload Creation: Serializes ServiceInfo to JSON (supports custom subclasses)
6. Registration Request: Sends POST to orchestrator endpoint
7. Retry on Failure: Retries with delay if request fails
8. Logging: Logs all attempts and final outcome

Registration Payload

The service sends this payload to the orchestrator:

{
  "url": "http://my-service:8000",
  "info": {
    "display_name": "My Service",
    "version": "1.0.0",
    "summary": "Service description",
    ...
  }
}

For custom ServiceInfo subclasses:

{
  "url": "http://ml-service:8000",
  "info": {
    "display_name": "ML Service",
    "version": "2.0.0",
    "deployment_env": "production",
    "team": "data-science",
    "capabilities": ["ml-inference", "feature-extraction"],
    "priority": 5
  }
}

Hostname Resolution

Priority order:

1. Direct Parameter: host="my-service" in .with_registration()
2. Auto-Detection: socket.gethostname() (returns Docker container name or hostname)
3. Environment Variable: Value of SERVICEKIT_HOST (or custom env var)
4. Error: Raises exception if fail_on_error=True, otherwise logs warning

Docker Behavior: In Docker Compose, socket.gethostname() returns the service name or container ID, making auto-detection work seamlessly.

Port Resolution

Priority order:

1. Direct Parameter: port=8080 in .with_registration()
2. Environment Variable: Value of SERVICEKIT_PORT (or custom env var)
3. Default: 8000

Important: SERVICEKIT_PORT should match the container's internal port, not the host-mapped port.

---

Examples

Environment Variables (Production)

from servicekit.api import BaseServiceBuilder, ServiceInfo

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="Production Service"))
    .with_logging()
    .with_health()
    .with_registration()  # Reads from environment
    .build()
)

docker-compose.yml:

services:
  my-service:
    image: my-service:latest
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register
      # SERVICEKIT_HOST auto-detected
      # SERVICEKIT_PORT defaults to 8000

Direct Configuration (Testing)

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="Test Service"))
    .with_registration(
        orchestrator_url="http://localhost:9000/services/$register",
        host="test-service",
        port=8080,
    )
    .build()
)

Custom Environment Variable Names

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="My Service"))
    .with_registration(
        orchestrator_url_env="MY_APP_ORCHESTRATOR_URL",
        host_env="MY_APP_HOST",
        port_env="MY_APP_PORT",
    )
    .build()
)

Environment:

export MY_APP_ORCHESTRATOR_URL=http://orchestrator:9000/services/$register
export MY_APP_HOST=my-service
export MY_APP_PORT=8000

Fail-Fast Mode

For critical services that must register:

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="Critical Service"))
    .with_registration(
        fail_on_error=True,  # Abort startup if registration fails
        max_retries=10,
        retry_delay=1.0,
    )
    .build()
)

Custom Retry Strategy

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="My Service"))
    .with_registration(
        max_retries=10,      # More attempts
        retry_delay=1.0,     # Faster retries
        timeout=5.0,         # Shorter timeout
    )
    .build()
)

---

Docker Compose

Basic Setup

services:
  orchestrator:
    image: orchestrator:latest
    ports:
      - "9000:9000"

  service-a:
    image: my-service:latest
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register
    depends_on:
      - orchestrator

With Health Checks

Wait for orchestrator to be healthy before starting services:

services:
  orchestrator:
    image: orchestrator:latest
    ports:
      - "9000:9000"
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:9000/health"]
      interval: 10s
      timeout: 5s
      retries: 3

  service-a:
    image: my-service:latest
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register
    depends_on:
      orchestrator:
        condition: service_healthy  # Wait for healthy status

Custom Port Mapping

When container port differs from host port:

services:
  service-a:
    image: my-service:latest
    ports:
      - "8001:8000"  # Host:Container
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register
      SERVICEKIT_PORT: "8000"  # Use container port, not host port

Why: Other services connect using the internal Docker network, so they use the container port (8000), not the host-mapped port (8001).

Multiple Services

services:
  orchestrator:
    image: orchestrator:latest
    ports:
      - "9000:9000"

  service-a:
    image: my-service:latest
    ports:
      - "8000:8000"
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register

  service-b:
    image: my-service:latest
    ports:
      - "8001:8000"
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register

Both services register with different hostnames (service-a, service-b) but same internal port (8000).

---

Kubernetes

ConfigMap for Orchestrator URL

apiVersion: v1
kind: ConfigMap
metadata:
  name: registration-config
data:
  orchestrator-url: "http://orchestrator-service:9000/services/$register"

Deployment with Registration

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-service
spec:
  replicas: 3
  template:
    metadata:
      labels:
        app: my-service
    spec:
      containers:
        - name: my-service
          image: my-service:latest
          env:
            - name: SERVICEKIT_ORCHESTRATOR_URL
              valueFrom:
                configMapKeyRef:
                  name: registration-config
                  key: orchestrator-url
            - name: SERVICEKIT_HOST
              valueFrom:
                fieldRef:
                  fieldPath: metadata.name  # Pod name

Service Discovery

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-service
  ports:
    - port: 8000
      targetPort: 8000

---

Error Handling

Retry Behavior

By default, registration retries 5 times with 2-second delays:

.with_registration(
    max_retries=5,      # Total attempts
    retry_delay=2.0,    # Seconds between attempts
)

Example timeline: - Attempt 1: Immediate - Attempt 2: After 2 seconds - Attempt 3: After 4 seconds (2s + 2s) - Attempt 4: After 6 seconds - Attempt 5: After 8 seconds

Fail on Error

Default (fail_on_error=False): Service starts even if registration fails

.with_registration(fail_on_error=False)  # Log warning, continue

Fail-Fast (fail_on_error=True): Service aborts startup if registration fails

.with_registration(fail_on_error=True)  # Raise exception, abort

When to use fail-fast: - Critical services that require orchestrator awareness - Production environments with strict registration requirements - Services that cannot function without being registered

Structured Logging

All registration events are logged with structured data:

{
  "event": "registration.starting",
  "orchestrator_url": "http://orchestrator:9000/services/$register",
  "service_url": "http://my-service:8000",
  "host_source": "auto-detected",
  "port_source": "default",
  "max_retries": 5
}

Success:

{
  "event": "registration.success",
  "service_url": "http://my-service:8000",
  "attempt": 1,
  "status_code": 200
}

Failure:

{
  "event": "registration.attempt_failed",
  "service_url": "http://my-service:8000",
  "attempt": 1,
  "max_retries": 5,
  "error": "Connection refused",
  "error_type": "ConnectError"
}

---

Troubleshooting

Registration Fails

Check orchestrator is reachable:

# From service container
docker compose exec my-service curl http://orchestrator:9000/health

Check environment variables:

docker compose exec my-service env | grep SERVICEKIT

View registration logs:

docker compose logs my-service | grep registration

Hostname Auto-Detection Issues

Problem: Auto-detection fails or returns unexpected value

Solution: Override with environment variable

environment:
  SERVICEKIT_HOST: my-custom-hostname

Debug hostname detection:

docker compose exec my-service hostname
docker compose exec my-service python -c "import socket; print(socket.gethostname())"

Port Mismatch

Problem: Orchestrator cannot reach service at registered URL

Common mistake: Using host-mapped port instead of container port

# WRONG
ports:
  - "8001:8000"
environment:
  SERVICEKIT_PORT: "8001"  # ❌ Host port

# CORRECT
ports:
  - "8001:8000"
environment:
  SERVICEKIT_PORT: "8000"  # ✅ Container port

Why: Services communicate via Docker's internal network using container ports, not host-mapped ports.

Orchestrator URL Missing

Problem: No orchestrator URL configured

Error: registration.missing_orchestrator_url

Solution: Set environment variable

export SERVICEKIT_ORCHESTRATOR_URL=http://orchestrator:9000/services/$register

Or use direct configuration:

.with_registration(orchestrator_url="http://orchestrator:9000/services/$register")

Service Not Appearing in Registry

Check orchestrator logs:

docker compose logs orchestrator

Check service startup logs:

docker compose logs my-service | grep registration

Verify orchestrator endpoint:

curl http://localhost:9000/services

---

Production Considerations

High Availability

Use multiple orchestrator replicas:

services:
  orchestrator:
    image: orchestrator:latest
    deploy:
      replicas: 3

  service-a:
    environment:
      SERVICEKIT_ORCHESTRATOR_URL: http://orchestrator:9000/services/$register

Retry Strategy

Adjust retries for production reliability:

.with_registration(
    max_retries=10,       # More attempts
    retry_delay=1.0,      # Faster retries
    timeout=30.0,         # Longer timeout
    fail_on_error=True,   # Fail fast in production
)

Security

Authentication: Add API keys or tokens to registration requests (requires custom implementation)

TLS: Use HTTPS for orchestrator communication

.with_registration(
    orchestrator_url="https://orchestrator:9443/services/$register"
)

Monitoring

Monitor registration health: - Track registration success/failure rates - Alert on repeated registration failures - Monitor orchestrator availability - Log all registration attempts for audit

---

Related Examples

• examples/registration/ - Complete registration demo with orchestrator
• core_api/ - Basic CRUD service
• monitoring/ - Prometheus metrics
• auth_envvar/ - Environment-based authentication

See Also

• Health Checks - Configure health endpoints
• Monitoring - Prometheus metrics
• Authentication - API key authentication