Preview features

Preview features in Dapr are considered experimental when they are first released.

Runtime preview features require explicit opt-in in order to be used. The runtime opt-in is specified in a preview setting feature in Dapr’s application configuration. See How-To: Enable preview features for more information.

For CLI there is no explicit opt-in, just the version that this was first made available.

Current preview features

Feature	Description	Setting	Documentation	Version introduced
App Middleware	Allow middleware components to be executed when making service-to-service calls	N/A	App Middleware	v1.9
Streaming for HTTP service invocation	Enables (partial) support for using streams in HTTP service invocation; see below for more details.	ServiceInvocationStreaming	Details	v1.10
App health checks	Allows configuring app health checks	AppHealthCheck	App health checks	v1.9
Pluggable components	Allows creating self-hosted gRPC-based components written in any language that supports gRPC. The following component APIs are supported: State stores, Pub/sub, Bindings	N/A	Pluggable components concept	v1.9
Multi-App Run	Configure multiple Dapr applications from a single configuration file and run from a single command	dapr run -f	Multi-App Run	v1.10
Workflows	Author workflows as code to automate and orchestrate tasks within your application, like messaging, state management, and failure handling	N/A	Workflows concept	v1.10

Streaming for HTTP service invocation

Running Dapr with the ServiceInvocationStreaming feature flag enables partial support for handling data as a stream in HTTP service invocation. This can offer improvements in performance and memory utilization when using Dapr to invoke another service using HTTP with large request or response bodies.

The table below summarizes the current state of support for streaming in HTTP service invocation in Dapr, including the impact of enabling ServiceInvocationStreaming, in the example where “app A” is invoking “app B” using Dapr. There are six steps in the data flow, with various levels of support for handling data as a stream:

Step	Handles data as a stream	Dapr 1.10	Dapr 1.10 with ServiceInvocationStreaming
1	Request: “App A” to “Dapr sidecar A	❌	❌
2	Request: “Dapr sidecar A” to “Dapr sidecar B	❌	✅
3	Request: “Dapr sidecar B” to “App B”	✅	✅
4	Response: “App B” to “Dapr sidecar B”	✅	✅
5	Response: “Dapr sidecar B” to “Dapr sidecar A	❌	✅
6	Response: “Dapr sidecar A” to “App A	❌	✅

Important notes:

• ServiceInvocationStreaming needs to be applied on caller sidecars only.
  In the example above, streams are used for HTTP service invocation if ServiceInvocationStreaming is applied to the configuration of “app A” and its Dapr sidecar, regardless of whether the feature flag is enabled for “app B” and its sidecar.
• When ServiceInvocationStreaming is enabled, you should make sure that all services your app invokes using Dapr (“app B”) are updated to Dapr 1.10, even if ServiceInvocationStreaming is not enabled for those sidecars.
  Invoking an app using Dapr 1.9 or older is still possible, but those calls may fail if you have applied a Dapr Resiliency policy with retries enabled.

Full support for streaming for HTTP service invocation will be completed in a future Dapr version.