lambda

--- name: lambda description: AWS Lambda serverless functions for event-driven compute. Use when creating functions, configuring triggers, debugging invocations, optimizing cold starts, setting up event source mappings, or managing layers. last_updated: "2026-01-07" doc_source: https://docs.aws.amazon.com/lambda/latest/dg/ ---

# AWS Lambda

AWS Lambda runs code without provisioning servers. You pay only for compute time consumed. Lambda automatically scales from a few requests per day to thousands per second.

## Table of Contents

- [Core Concepts](#core-concepts) - [Common Patterns](#common-patterns) - [CLI Reference](#cli-reference) - [Best Practices](#best-practices) - [Troubleshooting](#troubleshooting) - [References](#references)

## Core Concepts

### Function

Your code packaged with configuration. Includes runtime, handler, memory, timeout, and IAM role.

### Invocation Types

| Type | Description | Use Case | |------|-------------|----------| | **Synchronous** | Caller waits for response | API Gateway, direct invoke | | **Asynchronous** | Fire and forget | S3, SNS, EventBridge | | **Poll-based** | Lambda polls source | SQS, Kinesis, DynamoDB Streams |

### Execution Environment

Lambda creates execution environments to run your function. Components: - **Cold start**: New environment initialization - **Warm start**: Reusing existing environment - **Handler**: Entry point function - **Context**: Runtime information

### Layers

Reusable packages of libraries, dependencies, or custom runtimes (up to 5 per function).

## Common Patterns

### Create a Python Function

**AWS CLI:**

```bash # Create deployment package zip function.zip lambda_function.py

# Create function aws lambda create-function \ --function-name MyFunction \ --runtime python3.12 \ --role arn:aws:iam::123456789012:role/lambda-role \ --handler lambda_function.handler \ --zip-file fileb://function.zip \ --timeout 30 \ --memory-size 256

# Update function code aws lambda update-function-code \ --function-name MyFunction \ --zip-file fileb://function.zip ```

**boto3:**

```python import boto3 import zipfile import io

lambda_client = boto3.client('lambda')

# Create zip in memory zip_buffer = io.BytesIO() with zipfile.ZipFile(zip_buffer, 'w') as zf: zf.writestr('lambda_function.py', ''' def handler(event, context): return {"statusCode": 200, "body": "Hello"} ''') zip_buffer.seek(0)

# Create function lambda_client.create_function( FunctionName='MyFunction', Runtime='python3.12', Role='arn:aws:iam::123456789012:role/lambda-role', Handler='lambda_function.handler', Code={'ZipFile': zip_buffer.read()}, Timeout=30, MemorySize=256 ) ```

### Add S3 Trigger

```bash # Add permission for S3 to invoke Lambda aws lambda add-permission \ --function-name MyFunction \ --statement-id s3-trigger \ --action lambda:InvokeFunction \ --principal s3.amazonaws.com \ --source-arn arn:aws:s3:::my-bucket \ --source-account 123456789012

# Configure S3 notification (see S3 skill) ```

### Add SQS Event Source

```bash aws lambda create-event-source-mapping \ --function-name MyFunction \ --event-source-arn arn:aws:sqs:us-east-1:123456789012:my-queue \ --batch-size 10 \ --maximum-batching-window-in-seconds 5 ```

### Environment Variables

```bash aws lambda update-function-configuration \ --function-name MyFunction \ --environment "Variables={DB_HOST=mydb.cluster-xyz.us-east-1.rds.amazonaws.com,LOG_LEVEL=INFO}" ```

### Create and Attach Layer

```bash # Create layer zip -r layer.zip python/

aws lambda publish-layer-version \ --layer-name my-dependencies \ --compatible-runtimes python3.12 \ --zip-file fileb://layer.zip

# Attach to function aws lambda update-function-configuration \ --function-name MyFunction \ --layers arn:aws:lambda:us-east-1:123456789012:layer:my-dependencies:1 ```

### Invoke Function

```bash # Synchronous invoke aws lambda invoke \ --function-name MyFunction \ --payload '{"key": "value"}' \ response.json

# Asynchronous invoke aws lambda invoke \ --function-name MyFunction \ --invocation-type Event \ --payload '{"key": "value"}' \ response.json ```

## CLI Reference

### Function Management

| Command | Description | |---------|-------------| | `aws lambda create-function` | Create new function | | `aws lambda update-function-code` | Update function code | | `aws lambda update-function-configuration` | Update settings | | `aws lambda delete-function` | Delete function | | `aws lambda list-functions` | List all functions | | `aws lambda get-function` | Get function details |

### Invocation

| Command | Description | |---------|-------------| | `aws lambda invoke` | Invoke function | | `aws lambda invoke-async` | Async invoke (deprecated) |

### Event Sources

| Command | Description | |---------|-------------| | `aws lambda create-event-source-mapping` | Add event source | | `aws lambda list-event-source-mappings` | List mappings | | `aws lambda update-event-source-mapping` | Update mapping | | `aws lambda delete-event-source-mapping` | Remove mapping |

### Permissions

| Command | Description | |---------|-------------| | `aws lambda add-permission` | Add resource-based policy | | `aws lambda remove-permission` | Remove permission | | `aws lambda get-policy` | View resource policy |

## Best Practices

### Performance

- **Right-size memory**: More memory = more CPU = faster execution - **Minimize cold starts**: Keep functions warm, use Provisioned Concurrency - **Optimize package size**: Smaller packages deploy faster - **Use layers** for shared dependencies - **Initialize outside handler**: Reuse connections across invocations

```python # GOOD: Initialize outside handler import boto3 dynamodb = boto3.resource('dynamodb') table = dynamodb.Table('MyTable')

def handler(event, context): # Reuses existing connection return table.get_item(Key={'id': event['id']}) ```

### Security

- **Least privilege IAM roles** — only grant needed permissions - **Use Secrets Manager** for sensitive data - **Enable VPC** only if needed (adds latency) - **Encrypt environment variables** with KMS

### Cost Optimization

- **Set appropriate timeout** — don't use max 15 minutes unnecessarily - **Use ARM architecture** (Graviton2) for 34% better price/performance - **Batch process** where possible - **Use Reserved Concurrency** to limit costs

### Reliability

- **Configure DLQ** for async invocations - **Handle retries** — async events retry twice - **Make handlers idempotent** - **Use structured logging**

## Troubleshooting

### Timeout Errors

**Symptom:** `Task timed out after X seconds`

**Causes:** - Function takes longer than timeout - Network call to unreachable resource - VPC configuration issues

**Debug:**

```bash # Check function configuration aws lambda get-function-configuration \ --function-name MyFunction \ --query "Timeout"

# Increase timeout aws lambda update-function-configuration \ --function-name MyFunction \ --timeout 60 ```

### Out of Memory

**Symptom:** Function crashes with memory error

**Fix:**

```bash aws lambda update-function-configuration \ --function-name MyFunction \ --memory-size 512 ```

### Cold Start Latency

**Causes:** - Large deployment package - VPC configuration - Many dependencies to load

**Solutions:** - Use Provisioned Concurrency - Reduce package size - Use layers for dependencies - Consider Graviton2 (ARM)

```bash # Enable Provisioned Concurrency aws lambda put-provisioned-concurrency-config \ --function-name MyFunction \ --qualifier LIVE \ --provisioned-concurrent-executions 5 ```

### Permission Denied

**Symptom:** `AccessDeniedException`

**Debug:**

```bash # Check execution role aws lambda get-function-configuration \ --function-name MyFunction \ --query "Role"

# Check role policies aws iam list-attached-role-policies \ --role-name lambda-role ```

### VPC Connectivity Issues

**Symptom:** Cannot reach internet or AWS services

**Causes:** - No NAT Gateway for internet access - Missing VPC endpoint for AWS services - Security group blocking outbound

**Solutions:** - Add NAT Gateway for internet - Add VPC endpoints for AWS services - Check security group rules

## References

- [Lambda Developer Guide](https://docs.aws.amazon.com/lambda/latest/dg/) - [Lambda API Reference](https://docs.aws.amazon.com/lambda/latest/api/) - [Lambda CLI Reference](https://docs.aws.amazon.com/cli/latest/reference/lambda/) - [boto3 Lambda](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/lambda.html)