Reversible App Sample – New README

This sample shows a reversible architecture where you can switch messaging backends without changing application code. Dapr pub/sub abstracts the broker so you can run locally with RabbitMQ or in a cloud-like mode with Azure Service Bus. The startup scripts automatically stop any existing environment and build containers when needed; after that, switching backends reuses the same images.

What the sample does

• Java services (Spring Boot)
  • reversible-api (API): publishes customer events through Dapr
  • reversible-observer (Observer): subscribes to the same events via Dapr
• React customer-webapp UI to interact with the API
• PostgreSQL for persistence (pre-seeded data)
• Dapr sidecars + components for pub/sub
• Aspire Dashboard for local telemetry

The API emits customer events to the Dapr pub/sub component. The Observer subscribes to the topic and logs what it receives. You can confirm this behavior by tailing the observer container logs.

Build once, switch freely

• First run of either start script will build the Docker images if they’re missing (no separate build step required).
• When you switch between RabbitMQ and Azure Service Bus, you don’t need to rebuild the images. The Dapr components change, not the Java or React code.
• You don’t need to run a separate stop script—the start scripts stop any existing environment automatically.

Azure prerequisites (for Azure Service Bus mode)

When running the Azure environment, you need an existing Azure Service Bus with a topic for the sample’s events:

• Create (or reuse) a Service Bus namespace
• Create a Topic named customer-events
• Get the connection string (with Manage or Send/Listen as appropriate)
• Put the connection string in docker/dapr/secrets.json under the key servicebus-connection-string
  • See docker/dapr/secrets.json.sample for the expected JSON structure

Dapr’s Azure Service Bus component (docker/dapr/components-azure/pubsub.yaml) reads that secret via the local file secret store (docker/dapr/components-azure/secrets.yaml).

How to start the environments

Prerequisites:

• Windows with PowerShell (pwsh)
• Docker Desktop running

From the repo root, pick one mode:

Option A: Local with RabbitMQ

1. (Optional) Create secrets file if you don’t have one yet:

Copy-Item docker/dapr/secrets.json.sample docker/dapr/secrets.json -ErrorAction SilentlyContinue
# For RabbitMQ mode, you can keep only the Service Bus key empty; RabbitMQ connection is embedded in the component config.

2. Start:

pwsh ./start-rabbitmq.ps1

Services and endpoints:

• Webapp: http://localhost:8083
• API: http://localhost:8081
• Observer: http://localhost:8090
• PostgreSQL: localhost:5432
• RabbitMQ Management: http://localhost:15672 (admin/admin123)
• Aspire Dashboard: http://localhost:18888

Option B: Cloud-like with Azure Service Bus

1. Create secrets file and set your connection string:

Copy-Item docker/dapr/secrets.json.sample docker/dapr/secrets.json
# Edit docker/dapr/secrets.json and set:
# {
#   "servicebus-connection-string": "Endpoint=sb://<yournamespace>.servicebus.windows.net/;SharedAccessKeyName=<name>;SharedAccessKey=<key>"
# }

2. Start:

pwsh ./start-azure.ps1

Services and endpoints:

• Webapp: http://localhost:8083
• API: http://localhost:8081
• Observer: http://localhost:8090
• PostgreSQL: localhost:5432
• Aspire Dashboard: http://localhost:18888

Seeing the observer consume messages

The observer subscribes to the customer-events topic (via Dapr Subscription). To watch it process messages, stream logs from the observer container:

# Azure Service Bus mode
docker-compose -f docker/docker-compose-azure.yml logs -f observer

# RabbitMQ mode
docker-compose -f docker/docker-compose-rabbitmq.yml logs -f observer

You should see log entries whenever you interact with the app (e.g., creating/updating customers through the API/webapp).

Switching backends

To switch backends, just run the other start script. It will stop the currently running environment automatically and start the selected one:

# From Azure -> RabbitMQ
pwsh ./start-rabbitmq.ps1

# From RabbitMQ -> Azure (ensure your Service Bus connection string is set)
pwsh ./start-azure.ps1

No application code changes are needed; Dapr components handle the difference.

Notes and tips

• If a start script fails early, ensure Docker Desktop is running and that required files exist:
  • docker/dapr/secrets.json with servicebus-connection-string for Azure mode
• Use the Aspire Dashboard at http://localhost:18888 to inspect traces and logs.

Contributing

This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit Contributor License Agreements.

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This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.

Trademarks

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