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.
apm install @itsmostafa/lambda
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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)