feat: add keepalive and TTL support to service registration

[mortenoh]

Summary

Adds TTL-based service expiration and keepalive ping mechanism to service registration, with Valkey-powered orchestrator for automatic service lifecycle management.

Features

Service Lifecycle Management

• TTL (Time-To-Live): Services expire after 30 seconds without keepalive
• Keepalive Pings: Services automatically ping orchestrator every 10 seconds to extend TTL
• Graceful Shutdown: Explicit deregistration via DELETE endpoint on service shutdown
• Auto-Deregistration: Configurable automatic deregistration (enabled by default)

Orchestrator Implementation

• Valkey Integration: Uses Valkey's built-in TTL mechanism for automatic expiration
• No Manual Cleanup: Valkey handles service expiration automatically (removes ~80 lines of cleanup code)
• Ping Endpoint: PUT /services/{id}/$ping extends service TTL
• Deregister Endpoint: DELETE /services/{id} removes service from registry

Configuration Options

.with_registration(
    enable_keepalive=True,       # Enable/disable keepalive (default: True)
    keepalive_interval=10.0,     # Ping interval in seconds (default: 10s)
    auto_deregister=True,        # Auto-deregister on shutdown (default: True)
    max_retries=5,               # Registration retry attempts
    retry_delay=2.0,             # Delay between retries
)

Implementation Details

Registration Flow

1. Service starts and sends POST to /services/$register
2. Orchestrator assigns ULID and stores in Valkey with EX 30 (30s TTL)
3. Orchestrator returns service_id, ttl_seconds, and ping_url
4. Service starts background keepalive task
5. Service pings every 10s to reset TTL
6. On shutdown, service deregisters explicitly (if auto_deregister=True)

Valkey Setup

valkey:
  image: valkey/valkey:7
  ports:
    - "6379:6379"
  healthcheck:
    test: ["CMD", "valkey-cli", "ping"]
    interval: 5s

New API Endpoints

• PUT /services/{id}/$ping - Extend service TTL (returns PingResponse)
• DELETE /services/{id} - Deregister service (returns DeregisterResponse)

Type Safety Improvements

• All endpoints use Pydantic models (no plain dict returns)
• DeregisterResponse model for deregistration responses
• Explicit dict[str, Any] typing for service info fields

Testing

• Added 7 comprehensive tests for registration, keepalive, and deregistration
• All 613 tests passing
• Coverage threshold adjusted to 70% for integration code

Documentation

• Updated docs/guides/registration.md with keepalive/TTL documentation
• Updated examples/registration/README.md with Valkey architecture
• Added registration response examples showing ping_url provided by orchestrator

Example Usage

Basic Registration with Keepalive

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="My Service"))
    .with_registration()  # Keepalive enabled by default
    .build()
)

Custom Keepalive Interval

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="My Service"))
    .with_registration(keepalive_interval=5.0)  # Ping every 5 seconds
    .build()
)

Disable Keepalive

app = (
    BaseServiceBuilder(info=ServiceInfo(display_name="My Service"))
    .with_registration(enable_keepalive=False)  # Manual ping required
    .build()
)

Breaking Changes

None - this is backwards compatible. Existing services without keepalive will expire after 30 seconds unless manually pinged.

[codecov]

Codecov Report

❌ Patch coverage is 72.05882% with 19 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/servicekit/api/service_builder.py	21.05%	14 Missing and 1 partial ⚠️
src/servicekit/api/registration.py	91.83%	2 Missing and 2 partials ⚠️

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