Dapr uses a modular design where functionality is delivered as a component. Each component has an interface definition. All of the components are pluggable so that you can swap out one component with the same interface for another. The components contrib repo is where you can contribute implementations for the component interfaces and extends Dapr’s capabilities.
A building block can use any combination of components. For example the actors building block and the state management building block both use state components. As another example, the Pub/Sub building block uses Pub/Sub components.
You can get a list of current components available in the current hosting environment using the
dapr components CLI command.
The following are the component types provided by Dapr:
State store components are data stores (databases, files, memory) that store key-value pairs as part of the state management building block.
Service discovery components are used with the service invocation building block to integrate with the hosting environment to provide service-to-service discovery. For example, the Kubernetes service discovery component integrates with the Kubernetes DNS service and self hosted uses mDNS.
Dapr allows custom middleware to be plugged into the request processing pipeline. Middleware can perform additional actions on a request, such as authentication, encryption and message transformation before the request is routed to the user code, or before the request is returned to the client. The middleware components are used with the service invocation building block.
Pub/sub broker components are message brokers that can pass messages to/from services as part of the publish & subscribe building block.
External resources can connect to Dapr in order to trigger a service or be called from a service as part of the bindings building block.
In Dapr, a secret is any piece of private information that you want to guard against unwanted users. Secrets stores are used to store secrets that can be retrieved and used in services.