# Creating an Order Processing System with Lambda Durable Functions
<a name="order-processing-app"></a>

**Note**  
NEED: Add architecture diagram showing API Gateway, Durable Function workflow, and supporting services (DynamoDB, EventBridge)

## Prerequisites
<a name="order-processing-prerequisites"></a>
+ AWS CLI installed and configured
+ NEED: Specific Durable Functions requirements

## Create the Source Code Files
<a name="order-processing-source"></a>

Create the following files in your project directory:
+ `lambda_function.py` - the function code
+ `requirements.txt` - dependencies manifest

### Function Code
<a name="order-processing-function-code"></a>

```
# NEED: Verify correct imports
import boto3
import json

def lambda_handler(event, context):
    # NEED: Verify DurableContext syntax
    durable = context.durable
    
    try:
        # Validate and store order
        order = await durable.step('validate', async () => {
            return validate_order(event['order'])
        })
        
        # Process payment
        # NEED: Verify wait syntax
        await durable.wait(/* wait configuration */)
        
        # Additional steps
        # NEED: Complete implementation
        
    except Exception as e:
        # NEED: Error handling patterns
        raise e

def validate_order(order_data):
    # NEED: Implementation
    pass
```

### Requirements File
<a name="order-processing-requirements"></a>

```
# NEED: List of required packages
```

## Deploy the App
<a name="order-processing-deploy"></a>

### Create a DynamoDB Table for Orders
<a name="order-processing-dynamodb"></a>

1. Open the DynamoDB console at [https://console.aws.amazon.com/dynamodb/](https://console.aws.amazon.com/dynamodb/)

1. Choose **Create table**

1. For **Table name**, enter **Orders**

1. For **Partition key**, enter **orderId**

1. Leave other settings as default

1. Choose **Create table**

### Create the Lambda Function
<a name="order-processing-lambda"></a>

1. Open the Lambda console at [https://console.aws.amazon.com/lambda/](https://console.aws.amazon.com/lambda/)

1. Choose **Create function**

1. Select **Author from scratch**

1. For **Function name**, enter **ProcessOrder**

1. For **Runtime**, choose your preferred runtime

1. NEED: Add Durable Functions-specific configuration

1. Choose **Create function**

### Create the API Gateway Endpoint
<a name="order-processing-apigateway"></a>

1. Open the API Gateway console at [https://console.aws.amazon.com/apigateway/](https://console.aws.amazon.com/apigateway/)

1. Choose **Create API**

1. Select **HTTP API**

1. Choose **Build**

1. Add an integration with your Lambda function

1. Configure routes for order processing

1. Deploy the API

## Test the App
<a name="order-processing-test"></a>

Submit a test order:

```
{
    "orderId": "12345",
    "items": [
        {
            "productId": "ABC123",
            "quantity": 1
        }
    ]
}
```

NEED: Add specific monitoring instructions for Durable Functions

## Next Steps
<a name="order-processing-next-steps"></a>

### Add Business Logic
<a name="order-processing-business-logic"></a>

Implement inventory management:

```
async def check_inventory(order):
    # Add inventory check logic
    pass
```

Add price calculations:

```
async def calculate_total(order):
    # Add pricing logic
    pass
```

### Improve Error Handling
<a name="order-processing-error-handling"></a>

Add compensation logic:

```
async def reverse_payment(order):
    # Add payment reversal logic
    pass
```

Handle order cancellations:

```
async def cancel_order(order):
    # Add cancellation logic
    pass
```

### Integrate External Systems
<a name="order-processing-integrations"></a>

```
async def notify_shipping_provider(order):
    # Add shipping integration
    pass

async def send_customer_notification(order):
    # Add notification logic
    pass
```

### Enhance Monitoring
<a name="order-processing-monitoring"></a>
+ Create CloudWatch dashboards
+ Set up metrics for order processing times
+ Configure alerts for delayed orders