aws-lambda

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• SKILL.md

SKILL.md (first lines)

# AWS Lambda

Build serverless applications with AWS Lambda, covering function creation, event sources, layers, SAM templates, and cold start optimization.

## When to Use This Skill

- Building event-driven applications triggered by API Gateway, S3, SQS, or EventBridge
- Running scheduled tasks (cron) without managing servers
- Processing data streams from Kinesis or DynamoDB
- Building lightweight APIs with API Gateway or function URLs
- Implementing webhooks, Slack bots, or automation scripts
- Reducing compute costs for intermittent or bursty workloads

## Prerequisites

- AWS CLI v2 installed and configured
- Least-privilege IAM actions for the chosen resources; restrict `iam:PassRole` to the execution role. Wildcard service grants are not a prerequisite.
- Python 3.11+, Node.js 20+, or another supported runtime installed locally
- (Optional) AWS SAM CLI for local development and deployment

## Create and Deploy a Function

```bash
# Create a deployment package
cd my-function
zip -r function.zip app.py

# Create the Lambda function
aws lambda create-function \
  --function-name my-api-handler \
  --runtime python3.12 \
  --handler app.handler \
  --role arn:aws:iam::123456789012:role/LambdaExecRole \
  --zip-file fileb://function.zip \
  --memory-size 256 \
  --timeout 30 \
  --environment 'Variables={STAGE=production,LOG_LEVEL=INFO}' \
  --architectures arm64 \
  --tracing-config Mode=Active \
  --tags '{"Team":"backend","Environment":"production"}'

# Update function code
aws lambda update-function-code \
  --function-name my-api-handler \
  --zip-file fileb://function.zip

# Update function configuration
aws lambda update-function-configuration \
  --function-name my-api-handler \
  --memory-size 512 \
  --timeout 60 \
  --environment 'Variables={STAGE=production,LOG_LEVEL=WARNING}'

# Publish a version (immutable snapshot)
aws lambda publish-version \
  --function-name my-api-handler \
  --description "v1.2.0 - added rate limiting"

# Create an alias pointing to the version
aws lambda create-alias \
  --function-name my-api-handler \
  --name live \
  --function-version 3

# Weighted alias for canary deployments (90% v3, 10% v4)
aws lambda update-alias \
  --function-name my-api-handler \
  --name live \
  --function-version 4 \
  --routing-config '{"AdditionalVersionWeights":{"3":0.9}}'
```

## Function Code Examples

```python
# app.py - API Gateway REST proxy (v1) sketch; not the function URL/v2 event shape
import json
import logging
import os

logger = logging.getLogger()
logger.setLevel(os.environ.get("LOG_LEVEL", "INFO"))

def handler(event, context):
    """Handle API Gateway proxy event."""
    logger.info("Request: %s %s", event["httpMethod"], event["path"])

    try:
        body = json.loads(event.get("body") or "{}")
        result = process_request(body)

        return {
            "statusCode": 200,
            "headers": {
                "Content-Type": "application/json",
                "X-Request-Id": context.aws_request_id
            },
            "body": json.dumps(result)
        }
    except ValueError as e:
        logger.warning("Validation error: %s", e)
        return {"statusCode": 400, "body": json.dumps({"error": str(e)})}
    except Exception as e:
        logger.exception("Unhandled error")
        return {"statusCode": 500, "body": json.dumps({"error": "Internal server error"})}

def process_request(body):
    return {"message": "OK", "data": body}
```

```python
# sqs_processor.py - SQS batch processor with partial failure reporting
import json
import logging

logger = logging.getLogger()
logger.setLevel("INFO")

def handler(event, context):

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