How to Mock a Service Registry in Python with an In-Memory Dict

A lightweight ServiceRegistry class backed by a dict, exposing register, unregister, lookup, list, and health-check methods.

Easy Python 3.9+ Aug 9, 2026 Microservices patterns 13 views 0 copies

microservices service-registry dictionary mock in-memory

Python code

37 lines

Python 3.9+

class ServiceRegistry:
    def __init__(self):
        self._services = {}

    def register(self, name, endpoint, version="1.0"):
        self._services[name] = {
            "endpoint": endpoint,
            "version": version,
            "status": "healthy"
        }

    def unregister(self, name):
        return self._services.pop(name, None)

    def get_service(self, name):
        return self._services.get(name)

    def list_services(self):
        return list(self._services.keys())

    def health_check(self, name):
        service = self._services.get(name)
        if service:
            return service["status"]
        return "unknown"


if __name__ == "__main__":
    registry = ServiceRegistry()
    registry.register("auth-service", "http://localhost:8001")
    registry.register("user-service", "http://localhost:8002", version="2.0")
    print("Registered:", registry.list_services())
    print("Auth:", registry.get_service("auth-service"))
    print("User status:", registry.health_check("user-service"))
    registry.unregister("auth-service")
    print("After unregister:", registry.list_services())
    print("Missing status:", registry.health_check("auth-service"))

Output

stdout

Registered: ['auth-service', 'user-service']
Auth: {'endpoint': 'http://localhost:8001', 'version': '1.0', 'status': 'healthy'}
User status: healthy
After unregister: ['user-service']
Missing status: unknown

How it works

The class wraps a plain dict (self._services) as the in-memory storage, keyed by service name. Each value is itself a small dict holding endpoint, version, and status, so get_service returns the full service metadata in one lookup. unregister uses dict.pop which returns the removed value or None if absent. health_check safely returns "unknown" when the key is missing, avoiding a KeyError. This pattern mirrors real service registries like Consul or etcd, but with zero external dependencies.

Common mistakes

Mutating the returned dict from `get_service` and accidentally changing the registry's internal state
Forgetting that `unregister` returns the removed service dict, which can be mistaken for a bool
Not using a lock or threading when sharing the registry across multiple threads

Variations

Use `defaultdict` to auto-create an empty service entry on first register
Replace the dict with an external store like Redis for persistence across processes

Real-world use cases

Caching service locations in a microservices demo before introducing a real discovery server.
Simulating a registry in unit tests to verify consumer code without network calls.
Storing dynamic endpoints for internal tools or feature flags updated at runtime.

How to Mock a Service Registry in Python with an In-Memory Dict

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

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How it works

Common mistakes

Variations

Real-world use cases

More from Microservices patterns

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