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Dapr services

Second State launched a new WebAssembly-based SDK for the Dapr API, which provides an easy way for Rust-based microservices in WasmEdge to interact with Dapr APIs and sidecar services.

The figure below shows a Dapr-enabled microservice running inside the WasmEdge sandbox.

Dapr WASM rust API


Before we start, ensure you have Rust and WasmEdge installed.

You also need to install the following tools.

The template project explanation

The template application showcases how Dapr and WasmEdge work together to support lightweight WebAssembly-based microservices in a cloud-native environment. The microservices are all written in Rust and compiled into WebAssembly.

This application consists of three microservices and a standalone web page that enables users to interact with the microservices using an HTML+JavaScript UI. It is a very typical JAMstack setup. Each microservice is attached to a Dapr sidecar, which provides a suite of valuable services commonly required by cloud-native microservices.

Dapr and WasmEdge

The WasmEdge's Dapr SDK is used to access Dapr sidecars from the microservice apps. Specifically, the grayscale microservice takes an image from an HTTP POST, turns it into grayscale, and returns the result image data in the HTTP response.

  • It uses Dapr to discover and invoke the events microservice to record every successful user request.
  • It also stores each user’s IP address and last timestamp data in its Dapr sidecar’s state database. That allows the service to rate limit users if needed.

The classify microservices takes an image from an HTTP POST, runs a Tensorflow model against it to classify the object on the image, and returns the result as a text label in the HTTP response. You can learn more about AI inference in Rust and WasmEdge here. It uses its own Dapr sidecar like the grayscale microservice.

The events microservice takes JSON data from an HTTP POST and saves it to an external MySQL database for later analysis.

  • It uses Dapr to make itself discoverable by name by other microservices that need to record events.
  • It also uses its Dapr sidecar to store secrets such as MySQL database credentials.

Ok, enough concepts for the template project. Let's go ahead.

Live Demo | Tutorial video

Build and deploy these microservices in Dapr

First, start the database and place the connection string in the config/secrets.json file under DB_URL:MYSQL.

Next, start Dapr with the following commands.

dapr init

The image grayscale microservice


cd image-api-grayscale
cargo build --target wasm32-wasi --release
wasmedgec ./target/wasm32-wasi/release/image-api-grayscale.wasm image-api-grayscale.wasm


dapr run --app-id image-api-grayscale \
--app-protocol http \
--app-port 9005 \
--dapr-http-port 3503 \
--components-path ../config \
--log-level debug \
wasmedge image-api-grayscale.wasm

The image classification microservice


cd image-api-classify
cargo build --target wasm32-wasi --release
wasmedgec target/wasm32-wasi/release/wasmedge_hyper_server_tflite.wasm wasmedge_hyper_server_tflite.wasm


dapr run --app-id image-api-classify \
--app-protocol http \
--app-port 9006 \
--dapr-http-port 3504 \
--log-level debug \
--components-path ../config \
wasmedge-tensorflow-lite wasmedge_hyper_server_tflite.wasm

The events recorder microservice


cd events-service
cargo build --target wasm32-wasi --release
wasmedgec target/wasm32-wasi/release/events_service.wasm events_service.wasm


dapr run --app-id events-service \
--app-protocol http \
--app-port 9007 \
--dapr-http-port 3505 \
--log-level debug \
--components-path ../config \
wasmedge events_service.wasm


To test the services, you can use the static web page UI or curl.

Initialize the events database table.

$ curl http://localhost:9007/init

$ curl http://localhost:9007/events

Use the grayscale microservice. The return data is base64 encoded grayscale image.

$ cd docs
$ curl http://localhost:9005/grayscale -X POST --data-binary '@food.jpg'

Use the image classification microservice.

$ cd docs
$ curl http://localhost:9006/classify -X POST --data-binary '@food.jpg'
hotdog is detected with 255/255 confidence

Query the events database again.

$ curl http://localhost:9007/events

Next, you could use WasmEdge and WasmEdge's Dapr Rust API to create lightweight microservices with better security, faster performance, and smaller footprints.