EZToll - serverless toll system

EZToll takes pictures of license plates as input, converts them to toll events, and manages them through a REST API.

Service Requirements

1. Highly available
2. Scales with use to handle peak traffic hours
3. Serverless, pay per use
4. Durable, store events if processing fails
5. Store DynamoDB table logs for easy auditing

Service Flow

1. Images of license plates are uploaded to an S3 bucket under the key format of {id}/{timestamp} where id is the id of the toll booth and timestamp is the timestamp of when the image was taken.
2. This image triggers and S3 event which is stored in an SQS queue for durability until processesed.
3. The Lambda function extracts text information using Rekognition and uses another service to get current toll costs.
4. This information is uploaded to a DynamoDB table which holds toll even information.
5. Toll events can be queried by license plate number.
6. A toll can be resolved by sending a payment id for each toll event id. Payments are stored in an SQS queue for durability until processed.

Example

The following license plate image is uploaded as 12345/2021-09-06T13:00:00Z.jpg. This specifies 12345 as the id of the toll both and 2021-09-06T13:00:00Z.jpg as the timestamp of the image.

This gets processed through Amazon Rekognition and inserted into DynamoDB as the following item.

Then, the REST API can be queried like endpoint/tolls/ABC123, where ABC123 is the license plate number, and receive a list of tolls for that license plate.

{
    "tolls": [
        {
            "id": "1xssNTb05y5mR5VO87SH24vONEP",
            "timestamp": "2021-09-06T13:00:00Z",
            "plateNumber": "123ABC",
            "tollId": "12345",
            "paymentId": "",
            "cost": 2
        }
    ]
}

TODO

• return useful error messages for APIG endpoints/lambdas
• for stream processing, only return single message on failure. log reason for failure
• create toll client to modularize dynamodb table interaction
• use dynamodb UnmarshalListOfMaps
• use dynamodb expression for condition/values/names