Quickstart: Publish/Subscribe

This quickstart showcases how to enable the publish/subscribe pattern using the Pub/Sub API.

Prerequisites

Before you proceed, ensure you have the following prereqs installed.

Python

• Diagrid CLI
• Git
• Python 3.11+

.NET

• Diagrid CLI
• Git
• .NET 8.0+

JavaScript

• Diagrid CLI
• Git
• Node.JS LTS

Java

• Diagrid CLI
• Git
• Java 11.0+: OracleJDK or OpenJDK
• Apache Maven 3.9.5+

Log in to Catalyst

Authenticate to Diagrid Catalyst using the following command:

diagrid login 

Confirm your organization and user details are correct:

diagrid whoami

Deploy quickstart project

Create a project and bootstrap the necessary resources to begin developing locally with the Pubsub API. This command:

✔️ Creates a new Catalyst project
✔️ Deploys a Diagrid Pub/Sub service
✔️ Creates App IDs: one for the publishing application and one for the subscribing application
✔️ Clones a quickstart application to your machine
✔️ Scaffolds a dev config file to run the quickstart code with the necessary Catalyst connectivity info

Python

diagrid project quickstart --type pubsub --language python

.NET

diagrid project quickstart --type pubsub --language csharp

JavaScript

diagrid project quickstart --type pubsub --language javascript

Java

diagrid project quickstart --type pubsub --language java

After the command executes successfully, the CLI will output the contents of your newly created project including the two App IDs publisher and subscriber and a Diagrid KV Store called pubsub.

Run sample application

To run the quickstart code locally, you can use the diagrid dev start command. This command:

• Launches the local quickstart apps: Locates the code directories using the values specified for workDir and launches each application using the respective app command inputs
• Injects environment variables: Configures the Dapr client to talk to Catalyst using the publisher App ID API token
• Establishes private dev tunnel: Creates a private tunnel for the subscriber application on the specified appPort, which will route all traffic destined for the subscriber App ID to the local port where the code is running
• Streams application logs: Displays connectivity logs along with real-time app feedback directly in the terminal to make API testing simple

For additional details on the Catalyst local development experience, read Develop Locally with Catalyst APIs.

Python

Install python dependencies in a virtual environment.

note

This quickstart uses the venv module to create the virtual environment. Please feel free to adapt if you prefer to use conda, pipenv, or another alternative.

python -m venv venv

MacOS

If you are using MacOS, start the virtual environment with the following command:

source venv/bin/activate

tip

Don't forget to close your virtual environment with deactivate when done with the quickstart

Linux

If you are using Linux, start the virtual environment with the following command:

source venv/bin/activate

tip

Don't forget to close your virtual environment with deactivate when done with the quickstart

Windows

If you are using PowerShell on Windows, start the virtual environment with the following command:

venv/Scripts/Activate.ps1

If you are using the Command Prompt on Windows, start the virtual environment with the following command:

venv/Scripts/activate.bat

tip

If running in the Windows Command Prompt, don't forget to close your virtual environment with venv/Scripts/deactivate.bat when done with the quickstart

Install the python packages required by each service:

pip install -r ./publisher/requirements.txt  && pip install -r ./subscriber/requirements.txt

.NET

Restore .NET package dependencies required by each service:

donet restore ./publisher && donet restore ./subscriber

JavaScript

Install node packages and dependencies required by each service:

npm install --prefix ./publisher && npm install --prefix ./subscriber 

Java

Download and install maven dependencies required by each service:

mvn clean install -f ./publisher && mvn clean install -f ./subscriber

Run your applications and connect the subscriber App ID to the local subscriber app using the following command.

diagrid dev start 

tip

Ensure the log Connected App ID "subscriber" to localhost:5002 appears before proceeding to the next section.

Call the Publish API

With the quickstart application running, use the curl commands below or take advantage of the test.rest file in the root folder of the repo powered by the VS Code REST Client extension to trigger requests from the app to the Dapr Publish API hosted by Catalyst.

Open a new terminal and execute the following curl command:

curl -i -X POST http://localhost:5001/order -H "Content-Type: application/json" -d '{"orderId":1}'

Upon successful execution, the publisher app logs should show an indication that a message was successfully published, and the subscriber app logs should indicate the message was successfully received.

You can also view the published messages using the Diagrid Pub/Sub topic explorer. When the Pending Message Count is 0, it means the subscriber app has successfully processed all messages on the orders topic.

To stop the applications use CTL-C and to disconnect the local app connection from the subscriber App ID run the following:

diagrid dev stop

Clean up resources

If you are not going to continue to use this application, you can delete the Catalyst resoures using the following commands:

diagrid appid delete publisher 
diagrid appid delete subscriber

If you want to delete the entire Catalyst project, including the managed infrastructure resources, run the diagrid project delete command.