Karapace vs Pact

Karapace is a free, open-source implementation of the Kafka Schema Registry and Kafka REST Proxy. Its registry stores Avro, JSON Schema, and Protobuf schemas, keeps version histories, and checks compatibility between versions. The REST Proxy exposes HTTP APIs for producing and consuming Kafka events and handling administrative operations. Karapace implements the Confluent Schema Registry API and REST Proxy API versions 1 and 2, with version 2 as the default. A leader-and-replica design provides high availability and load balancing. Monitoring includes Prometheus-native metrics and OpenTelemetry traces and metrics, with optional Sentry reporting. Schema Registry authentication supports HTTP basic authentication and OAuth2/OIDC bearer-token validation; the REST Proxy forwards OAuth2 tokens instead of validating them. Karapace is self-hosted, requires Python 3.12 or newer, and installs from Docker images or source. Default Docker ports are 8081 for the Schema Registry and 8082 for the REST Proxy. It is offered at free.

Pact is a free, code-first tool for testing HTTP and message integrations with contract tests. Automated consumer tests create contracts describing concrete interactions between consumer and provider applications. Teams can then test each side in isolation against that shared contract, without deploying the entire system. Pact implementations are available for more than 10 languages, including JavaScript, Java, .NET, Go, Python, Ruby, Swift and Objective-C, Scala, Rust, PHP, and C++. Its CLI includes mock and stub servers, a provider verifier, a broker client, and a plugin CLI. The open-source Pact Broker shares contracts and verification results; teams can host and administer it themselves, and use its CI/CD workflows to check whether application versions can be deployed together. The verifier supports HTTP and asynchronous and synchronous messages, while plugins include gRPC, Avro, and CSV support. Documentation includes recipes for tools and scenarios such as GraphQL, Cypress, Kafka, and AWS Lambda. Pact is most useful when teams control both consumer and provider development. The free Broker is self-hosted, leaving its security, maintenance, and upgrades to its operator.