The main components of a Kalix service are:
The service interface and the domain data model (for Entities), are contained in individual
.proto files, as gRPC descriptors. Separating the service interface and data model in different files allows you to evolve them independently.
The gRPC definitions in
.proto files describe the external interface, messages, and events. From the
.proto files, the gRPC CLI (
protoc), generates the code framework for remote procedure calls, data access, and serialization. Take a look at Writing gRPC descriptors for more information about defining messages and events.
Stateful services can implement Value Entity, Event Sourced Entity, or Replicated Entity components. Stateless services implement Actions. Typically, a stateful service should only have one Entity type, but can also include Actions.
Actions are stateless functions that can be triggered by gRPC or HTTP calls. They can also subscribe to published events, and they can send commands to other services based on the events they receive. For more information about writing actions see Implementing Actions.
Stateful services encapsulate business logic in in Value Entities, Event Sourced Entities, or Replicated Entities. At runtime, command messages invoke operations on Entities. A command may only act on one Entity at a time.
|To learn more about Kalix entities see Implement a Value Entity, Implement an Event Sourced Entity, and Implement a Replicated Entity.|
To update multiple Entities from a single command use forwarding and effects.
Services can interact asynchronously with other services and with external systems. Event Sourced Entities emit events to a journal, to which other services can subscribe. By configuring your own publish/subscribe (pub/sub) mechanism, any service can publish their own events and subscribe to events published by other services or external systems.
For more details and examples take a look at the following topics:
You can test and debug your services by running them locally before deploying to Kalix.