Assignment 5 - Add a Dapr output binding

Assignment goals

To complete this assignment, you must reach the following goals:

• The FineCollectionService uses the Dapr SMTP output binding to send an email.
• The SMTP binding calls a development SMTP server that runs as part of the solution in a Docker container.

This assignment targets number 4 in the end-state setup:

Step 1: Run the SMTP server

In this assignment, you will use MailDev as your SMTP server. This is a development SMTP server that doesn't actually send out emails (by default), but collects them and shows them in an inbox type web application it has built-in. This is extremely handy in test or demo scenarios.

You will run this server as a Docker container:

1. Open the terminal window in VS Code.

2. Start a MailDev SMTP server by entering the following command:

   docker run -d -p 4000:1080 -p 4025:1025 --name dtc-maildev maildev/maildev:2.0.5
   

This will pull the docker image maildev/maildev:2.0.5 from Docker Hub and start it. The name of the container will be dtc-maildev. The server will be listening for connections on port 4025 for SMTP traffic and port 4000 for HTTP traffic. This last port is where the inbox web app will run for inspecting the emails.

If everything goes well, you should see some output like this:

❯ docker run -d -p 4000:1080 -p 4025:1025 --name dtc-maildev maildev/maildev:2.0.5
Unable to find image 'maildev/maildev:2.0.5' locally
2.0.5: Pulling from maildev/maildev
df9b9388f04a: Already exists
70c90f7de7cb: Pull complete
f83937c3ce37: Pull complete
98b78bba1d70: Pull complete
ee0959d18bfc: Pull complete
42bcb104f1ff: Pull complete
Digest: sha256:082ec5ee92266c6e17493998ff1bf1c3eb70604b159fbeeaa435ee777f5cc953
Status: Downloaded newer image for maildev/maildev:2.0.5
15460526eeec36fb10de920a92086797b69dab7638c7a7a8254d237346fd82e2

If you see any errors, make sure you have access to the Internet and are able to download images from Docker Hub. See Docker Hub for more info.

The container will keep running in the background. If you want to stop it, enter the following command:

docker stop dtc-maildev

You can then start the container later by entering the following command:

docker start dtc-maildev

If you are done using the container, you can also remove it by entering the following command:

docker rm dtc-maildev -f

Once you have removed it, you need to start it again with the docker run command shown at the beginning of this step.

For your convenience, the Infrastructure folder contains Powershell scripts for starting the infrastructural components you'll use throughout the workshop. You can use the Infrastructure/maildev/start-maildev.sh script to start the MailDev container.

If you don't mind starting all the infrastructural containers at once (also for assignments to come), you can also use the Infrastructure/start-all.sh script.

Step 2: Use the Dapr output binding in the FineCollectionService

You will add code to the FineCollectionService so it uses the Dapr SMTP output binding to send an email:

1. Open the file FineCollectionService/fine_collection/services.py in VS Code.

2. Inspect the code of the process_speed_violation method. There's a TODO comment at the end of the method. You'll add code to complete this TODO and actually send an email.

3. Add an import statement at the top of the file so you can invoke the binding using a REST request:

   import requests
   

4. Add the following code to the process_speed_violation method to replace the TODO comment:

   message_data = {
      "data": message_body,
      "operation": "create",
      "metadata": {
            "subject": "Fine for exceeding the speed limit.",
            "emailTo": vehicle.ownerEmail,
            "emailFrom": "test@domain.org"
      }
   }
   
   response = requests.post("http://localhost:3601/v1.0/bindings/sendmail", json=message_data)
   

   First, we create the message data containing the subject, sender, body, and recipient of the message. The message data also contains information about the operation that we want to invoke on the binding. Finally, we invoke the sendemail binding to send the message to the vehicle owner.

That's it, that's all the code you need to write to send an email over SMTP.

Step 3: Configure the output binding

In this step you will add a Dapr binding component configuration file to the custom components folder you created in Assignment 3.

1. Add a new file in the dapr/components folder named email.yaml.

2. Open this file in VS Code.

3. Paste this snippet into the file:

   apiVersion: dapr.io/v1alpha1
   kind: Component
   metadata:
     name: sendmail
   spec:
     type: bindings.smtp
     version: v1
     metadata:
     - name: host
       value: localhost
     - name: port
       value: 4025
     - name: user
       value: "_username"
     - name: password
       value: "_password"
     - name: skipTLSVerify
       value: true
   scopes:
     - finecollectionservice
   

As you can see, you specify the binding type SMTP (bindings.smtp) and you specify in the metadata how to connect to the SMTP server container you started in step 1 (running on localhost on port 4025). The other metadata can be ignored for now.

Important to notice with bindings is the name of the binding. This name must be the same as the name used in the call to the bindings API as you did in the code in step 2:

response = requests.post("http://localhost:3601/v1.0/bindings/sendmail", json=message_data)

Step 4: Test the application

You're going to start all the services now. You specify the custom components folder you've created on the command-line using the --resources-path flag so Dapr will use these config files:

1. Make sure no services from previous tests are running (close the terminal windows)

2. Make sure all the Docker containers introduced in the previous assignments are running (you can use the Infrastructure/start-all.ps1 script to start them).

3. Open the terminal window in VS Code and make sure the current folder is VehicleRegistrationService.

4. Enter the following command to run the VehicleRegistrationService with a Dapr sidecar:

   dapr run --app-id vehicleregistrationservice --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --resources-path ../dapr/components -- uvicorn vehicle_registration:app --port 6002
   

5. Open a new terminal window in VS Code and change the current folder to FineCollectionService.

6. Enter the following command to run the FineCollectionService with a Dapr sidecar:

   dapr run --app-id finecollectionservice --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --resources-path ../dapr/components -- uvicorn fine_collection:app --port 6001
   

7. Open a new terminal window in VS Code and change the current folder to TrafficControlService.

8. Enter the following command to run the TrafficControlService with a Dapr sidecar:

   dapr run --app-id trafficcontrolservice --app-port 6000 --dapr-http-port 3600 --dapr-grpc-port 60000 --resources-path ../dapr/components -- uvicorn traffic_control:app --port 6000
   

9. Open a new terminal window in VS Code and change the current folder to Simulation.

10. Start the simulation:

    python simulation
    

You should see the same logs as before. But now you should also be able to see the fine emails being sent by the FineCollectionService:

1. Open a browser and browse to http://localhost:4000.
2. Wait for the first emails to come in.
3. Click on an email in the inbox to see its content:

Next assignment

Make sure you stop all running processes and close all the terminal windows in VS Code before proceeding to the next assignment.

Go to assignment 6.