quickstarts/pub_sub/python/sdk

Dapr pub/sub

In this quickstart, you'll create a publisher microservice and a subscriber microservice to demonstrate how Dapr enables a publish-subcribe pattern. The publisher will generate messages of a specific topic, while subscribers will listen for messages of specific topics. See Why Pub-Sub to understand when this pattern might be a good choice for your software architecture.

Visit this link for more information about Dapr and Pub-Sub.

Note: This example leverages the Dapr client SDK. If you are looking for the example using only HTTP requests click here.

This quickstart includes one publisher:

• Python client message generator checkout

And one subscriber:

• Python subscriber order-processor

Run all apps with multi-app run template file:

This section shows how to run both applications at once using multi-app run template files with dapr run -f .. This enables to you test the interactions between multiple applications.

1. Install dependencies:

2. Run the Python subscriber app (flask version) with Dapr:

cd ./checkout
pip3 install -r requirements.txt
cd ..
cd ./order-processor
pip3 install -r requirements.txt
cd ..
cd ./order-processor-fastapi
pip3 install -r requirements.txt
cd ..

2. Open a new terminal window and run the multi app run template:

dapr run -f .

The terminal console output should look similar to this:

== APP - checkout-sdk == INFO:root:Published data: {"orderId": 1}
== APP - order-processor-sdk == Subscriber received : 1
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:19] "POST /orders HTTP/1.1" 200 -
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 2}
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:20] "POST /orders HTTP/1.1" 200 -
== APP - order-processor-sdk == Subscriber received : 2
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 3}
== APP - order-processor-sdk == Subscriber received : 3
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:21] "POST /orders HTTP/1.1" 200 -
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 4}
== APP - order-processor-sdk == Subscriber received : 4
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:22] "POST /orders HTTP/1.1" 200 -
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 5}
== APP - order-processor-sdk == Subscriber received : 5
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:23] "POST /orders HTTP/1.1" 200 -
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 6}
== APP - order-processor-sdk == Subscriber received : 6
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:24] "POST /orders HTTP/1.1" 200 -
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 7}
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:25] "POST /orders HTTP/1.1" 200 -
== APP - order-processor-sdk == Subscriber received : 7
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 8}
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:26] "POST /orders HTTP/1.1" 200 -
== APP - order-processor-sdk == Subscriber received : 8
== APP - checkout-sdk == INFO:root:Published data: {"orderId": 9}
== APP - order-processor-sdk == 127.0.0.1 - - [04/Sep/2023 11:15:27] "POST /orders HTTP/1.1" 200 -
== APP - order-processor-sdk == Subscriber received : 9

3. Stop and clean up application processes

dapr stop -f .

Run a single app at a time with Dapr (Optional)

An alternative to running all or multiple applications at once is to run single apps one-at-a-time using multiple dapr run .. -- python3 app.py commands. This next section covers how to do this.

Run Python message subscriber with Dapr

1. Install dependencies:

cd ./order-processor
pip3 install -r requirements.txt

2. Run the Python subscriber app with Dapr:

dapr run --app-id order-processor-sdk --resources-path ../../../components/ --app-port 6001 -- uvicorn app:app --port 6002

Run Python message publisher with Dapr

1. Install dependencies:

cd ./checkout
pip3 install -r requirements.txt 

2. Run the Python publisher app with Dapr:

dapr run --app-id checkout-sdk --resources-path ../../../components/ -- python3 app.py

Stop the apps and clean up

dapr stop --app-id checkout-sdk
dapr stop --app-id order-processor-sdk
dapr stop --app-id order-processor-sdk-fastapi