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Readme.md
Publish/Subcribe message broker
Dapr enables developers to design their application using the pub/sub pattern using a message broker, where event consumers and producers are decoupled from one another, and communicate by sending and receiving messages that are associated with a namespace, usually in the form of topics.
This allows event producers to send messages to consumers that aren't running, and consumers to receive messages based on subscriptions to topics.
Dapr provides At-Least-Once messaging guarantees, and integrates with various message brokers implementations. These implementations are pluggable, and developed outside of the Dapr runtime in components-contrib.
Publish/Subcribe API
The API for Publish/Subcribe can be found in the spec repo.
Behavior and guarantees
Dapr guarantees At-Least-Once semantics for message delivery.
That is, when an application publishes a message to a topic using the Publish/Subcribe API, it can assume the message is delivered at least once to any subscriber when the response status code from that endpoint is 200, or returns no error if using the gRPC client.
The burden of dealing with concepts like consumer groups and multiple instances inside consumer groups is all catered for by Dapr.
Dapr has the concept of an id. Dapr requires a single ID to be assigned to every application instance
When multiple instances of the same application type, each with their own ID, subscribe to a topic, Dapr invokes only one message instance for each application id. If two different applications with different IDs subscribe to a topic, at least one consumer in each application receives a copy of the same message.
Cloud Events
Dapr follows the Cloud Events 0.3 spec and wraps any payload sent to a topic inside a Cloud Events envelope.
The following fields from the Cloud Events spec are implemented with Dapr:
idsourcespecversiontypedatacontenttype(Optional)