Skip to content
aws-serverless · agentic-awesome-skills · Flowy
$ npx -y skills add sickn33/agentic-awesome-skills --skill aws-serverless --agent claude-codeInstalls just this skill. Get the whole plugin for auto-invocation.
⚡ How it fires
How this skill gets triggered: by you, by Claude, or both.
Fires itself Claude auto-loads it when your prompt matches the work. You can call it Invoke it directly when you want it. Slash command /aws-serverless👁️ Context preview
The summary Claude sees to decide when to auto-load this skill.
Specialized skill for building production-ready serverless 📦 Ships with agentic-awesome-skills
</> SKILL.md
aws-serverless.SKILL.md
---
name : aws-serverless
description : Specialized skill for building production-ready serverless
applications on AWS. Covers Lambda functions, API Gateway, DynamoDB, SQS/SNS
event-driven patterns, SAM/CDK deployment, and cold start optimization.
risk : unknown
source : vibeship-spawner-skills (Apache 2.0)
date_added : 2026-02-27
---
# AWS Serverless
Specialized skill for building production-ready serverless applications on AWS.
Covers Lambda functions, API Gateway, DynamoDB, SQS/SNS event-driven patterns,
SAM/CDK deployment, and cold start optimization.
## Principles
- Right-size memory and timeout (measure before optimizing)
- Minimize cold starts for latency-sensitive workloads
- Use SnapStart for Java/.NET functions
- Prefer HTTP API over REST API for simple use cases
- Design for failure with DLQs and retries
- Keep deployment packages small
- Use environment variables for configuration
- Implement structured logging with correlation IDs
## Patterns
### Lambda Handler Pattern
Proper Lambda function structure with error handling
Flowy AI Flows that just work. Hand-picked Claude Code plugins that fire the right skill as you prompt.
**When to use**: Any Lambda function implementation,API handlers, event processors, scheduled tasks
```javascript
// Node.js Lambda Handler
// handler.js
// Initialize outside handler (reused across invocations)
const { DynamoDBClient } = require('@aws-sdk/client-dynamodb');
const { DynamoDBDocumentClient, GetCommand } = require('@aws-sdk/lib-dynamodb');
const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);
// Handler function
exports.handler = async (event, context) => {
// Optional: Don't wait for event loop to clear (Node.js)
context.callbackWaitsForEmptyEventLoop = false;
try {
// Parse input based on event source
const body = typeof event.body === 'string'
? JSON.parse(event.body)
: event.body;
// Business logic
const result = await processRequest(body);
// Return API Gateway compatible response
return {
statusCode: 200,
headers: {
'Content-Type': 'application/json',
'Access-Control-Allow-Origin': '*'
},
body: JSON.stringify(result)
};
} catch (error) {
console.error('Error:', JSON.stringify({
error: error.message,
stack: error.stack,
requestId: context.awsRequestId
}));
return {
statusCode: error.statusCode || 500,
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({
error: error.message || 'Internal server error'
})
};
}
};
async function processRequest(data) {
// Your business logic here
const result = await docClient.send(new GetCommand({
TableName: process.env.TABLE_NAME,
Key: { id: data.id }
}));
return result.Item;
}
```
```python
# Python Lambda Handler
# handler.py
import json
import os
import logging
import boto3
from botocore.exceptions import ClientError
# Initialize outside handler (reused across invocations)
logger = logging.getLogger()
logger.setLevel(logging.INFO)
dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table(os.environ['TABLE_NAME'])
def handler(event, context):
try:
# Parse input
body = json.loads(event.get('body', '{}')) if isinstance(event.get('body'), str) else event.get('body', {})
# Business logic
result = process_request(body)
return {
'statusCode': 200,
'headers': {
'Content-Type': 'application/json',
'Access-Control-Allow-Origin': '*'
},
'body': json.dumps(result)
}
except ClientError as e:
logger.error(f"DynamoDB error: {e.response['Error']['Message']}")
return error_response(500, 'Database error')
except json.JSONDecodeError:
return error_response(400, 'Invalid JSON')
except Exception as e:
logger.error(f"Unexpected error: {str(e)}", exc_info=True)
return error_response(500, 'Internal server error')
def process_request(data):
response = table.get_item(Key={'id': data['id']})
return response.get('Item')
def error_response(status_code, message):
return {
'statusCode': status_code,
'headers': {'Content-Type': 'application/json'},
'body': json.dumps({'error': message})
}
```
### Best_practices
- Initialize clients outside handler (reused across warm invocations)
- Always return proper API Gateway response format
- Log with structured JSON for CloudWatch Insights
- Include request ID in error logs for tracing
### API Gateway Integration Pattern
REST API and HTTP API integration with Lambda
**When to use**: Building REST APIs backed by Lambda,Need HTTP endpoints for functions
```yaml
# template.yaml (SAM)
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Globals:
Function:
Runtime: nodejs20.x
Timeout: 30
MemorySize: 256
Environment:
Variables:
TABLE_NAME: !Ref ItemsTable
Resources:
# HTTP API (recommended for simple use cases)
HttpApi:
Type: AWS::Serverless::HttpApi
Properties:
StageName: prod
CorsConfiguration:
AllowOrigins:
- "*"
AllowMethods:
- GET
- POST
- DELETE
AllowHeaders:
- "*"
# Lambda Functions
GetItemFunction:
Type: AWS::Serverless::Function
Properties:
Handler: src/handlers/get.handler
Events:
GetItem:
Type: HttpApi
Properties:
ApiId: !Ref HttpApi
Path: /items/{id}
Method: GET
Policies:
- DynamoDBReadPolicy:
TableName: !Ref ItemsTable
CreateItemFunction:
Type: AWS::Serverless::Function
Properties:
Handler: src/handlers/create.handler
Events:
CreateItem:
Type: HttpApi
Properties:
ApiId: !Ref HttpApi
Path: /items
Method: POST
Policies:
- DynamoDBCrudPolicy:
TableName: !Ref ItemsTable
# DynamoDB Table
ItemsTable:
Type: AWS::DynamoDB::Table
Properties:
AttributeDefinitions:
- AttributeName: id
AttributeType: S
KeySchema:
- AttributeName: id
KeyType: HASH
BillingMode: PAY_PER_REQUEST
Outputs:
ApiUrl:
Value: !Sub "https://${HttpApi}.execute-api.${AWS::Region}.amazonaws.com/prod"
```
```javascript
// src/handlers/get.js
const { getItem } = require('../lib/dynamodb');
exports.handler = async (event) => {
const id = event.pathParameters?.id;
if (!id) {
return {
statusCode: 400,
body: JSON.stringify({ error: 'Missing id parameter' })
};
}
const item = await getItem(id);
if (!item) {
return {
statusCode: 404,
body: JSON.stringify({ error: 'Item not found' })
};
}
return {
statusCode: 200,
body: JSON.stringify(item)
};
};
```
### Structure
project/
├── template.yaml # SAM template
├── src/
│ ├── handlers/
│ │ ├── get.js
│ │ ├── create.js
│ │ └── delete.js
│ └── lib/
│ └── dynamodb.js
└── events/
└── event.json # Test events
### Api_comparison
- Http_api:
- Lower latency (~10ms)
- Lower cost (50-70% cheaper)
- Simpler, fewer features
- Best for: Most REST APIs
- Rest_api:
- More features (caching, request validation, WAF)
- Usage plans and API keys
- Request/response transformation
- Best for: Complex APIs, enterprise features
### Event-Driven SQS Pattern
Lambda triggered by SQS for reliable async processing
**When to use**: Decoupled, asynchronous processing,Need retry logic and DLQ,Processing messages in batches
```yaml
# template.yaml
Resources:
ProcessorFunction:
Type: AWS::Serverless::Function
Properties:
Handler: src/handlers/processor.handler
Events:
SQSEvent:
Type: SQS
Properties:
Queue: !GetAtt ProcessingQueue.Arn
BatchSize: 10
FunctionResponseTypes:
- ReportBatchItemFailures # Partial batch failure handling
ProcessingQueue:
Type: AWS::SQS::Queue
Properties:
VisibilityTimeout: 180 # 6x Lambda timeout
RedrivePolicy:
deadLetterTargetArn: !GetAtt DeadLetterQueue.Arn
maxReceiveCount: 3
DeadLetterQueue:
Type: AWS::SQS::Queue
Properties:
MessageRetentionPeriod: 1209600 # 14 days
```
```javascript
// src/handlers/processor.js
exports.handler = async (event) => {
const batchItemFailures = [];
for (const record of event.Records) {
try {
const body = JSON.parse(record.body);
await processMessage(body);
} catch (error) {
console.error(`Failed to process message ${record.messageId}:`, error);
// Report this item as failed (will be retried)
batchItemFailures.push({
itemIdentifier: record.messageId
});
}
}
// Return failed items for retry
return { batchItemFailures };
};
async function processMessage(message) {
// Your processing logic
console.log('Processing:', message);
// Simulate work
await saveToDatabase(message);
}
```
```python
# Python version
import json
import logging
logger = logging.getLogger()
def handler(event, context):
batch_item_failures = []
for record in event['Records']:
try:
body = json.loads(record['body'])
process_message(body)
except Exception as e:
logger.error(f"Failed to process {record['messageId']}: {e}")
batch_item_failures.append({
'itemIdentifier': record['messageId']
})
return {'batchItemFailures': batch_item_failures}
```
### Best_practices
- Set VisibilityTimeout to 6x Lambda timeout
- Use ReportBatchItemFailures for partial batch failure
- Always configure a DLQ for poison messages
- Process messages idempotently
### DynamoDB Streams Pattern
React to DynamoDB table changes with Lambda
**When to use**: Real-time reactions to data changes,Cross-region replication,Audit logging, notifications
```yaml
# template.yaml
Resources:
ItemsTable:
Type: AWS::DynamoDB::Table
Properties:
TableName: items
AttributeDefinitions:
- AttributeName: id
AttributeType: S
KeySchema:
- AttributeName: id
KeyType: HASH
BillingMode: PAY_PER_REQUEST
StreamSpecification:
StreamViewType: NEW_AND_OLD_IMAGES
StreamProcessorFunction:
Type: AWS::Serverless::Function
Properties:
Handler: src/handlers/stream.handler
Events:
Stream:
Type: DynamoDB
Properties:
Stream: !GetAtt ItemsTable.StreamArn
StartingPosition: TRIM_HORIZON
BatchSize: 100
MaximumRetryAttempts: 3
DestinationConfig:
OnFailure:
Destination: !GetAtt StreamDLQ.Arn
StreamDLQ:
Type: AWS::SQS::Queue
```
```javascript
// src/handlers/stream.js
exports.handler = async (event) => {
for (const record of event.Records) {
const eventName = record.eventName; // INSERT, MODIFY, REMOVE
// Unmarshall DynamoDB format to plain JS objects
const newImage = record.dynamodb.NewImage
? unmarshall(record.dynamodb.NewImage)
: null;
const oldImage = record.dynamodb.OldImage
? unmarshall(record.dynamodb.OldImage)
: null;
console.log(`${eventName}: `, { newImage, oldImage });
switch (eventName) {
case 'INSERT':
await handleInsert(newImage);
break;
case 'MODIFY':
await handleModify(oldImage, newImage);
break;
case 'REMOVE':
await handleRemove(oldImage);
break;
}
}
};
// Use AWS SDK v3 unmarshall
const { unmarshall } = require('@aws-sdk/util-dynamodb');
```
### Stream_view_types
- KEYS_ONLY: Only key attributes
- NEW_IMAGE: After modification
- OLD_IMAGE: Before modification
- NEW_AND_OLD_IMAGES: Both before and after
### Cold Start Optimization Pattern
Minimize Lambda cold start latency
**When to use**: Latency-sensitive applications,User-facing APIs,High-traffic functions
## 1. Optimize Package Size
```javascript
// Use modular AWS SDK v3 imports
// GOOD - only imports what you need
const { DynamoDBClient } = require('@aws-sdk/client-dynamodb');
const { DynamoDBDocumentClient, GetCommand } = require('@aws-sdk/lib-dynamodb');
// BAD - imports entire SDK
const AWS = require('aws-sdk'); // Don't do this!
```
## 2. Use SnapStart (Java/.NET)
```yaml
# template.yaml
Resources:
JavaFunction:
Type: AWS::Serverless::Function
Properties:
Handler: com.example.Handler::handleRequest
Runtime: java21
SnapStart:
ApplyOn: PublishedVersions # Enable SnapStart
AutoPublishAlias: live
```
## 3. Right-size Memory
```yaml
# More memory = more CPU = faster init
Resources:
FastFunction:
Type: AWS::Serverless::Function
Properties:
MemorySize: 1024 # 1GB gets full vCPU
Timeout: 30
```
## 4. Provisioned Concurrency (when needed)
```yaml
Resources:
CriticalFunction:
Type: AWS::Serverless::Function
Properties:
Handler: src/handlers/critical.handler
AutoPublishAlias: live
ProvisionedConcurrency:
Type: AWS::Lambda::ProvisionedConcurrencyConfig
Properties:
FunctionName: !Ref CriticalFunction
Qualifier: live
ProvisionedConcurrentExecutions: 5
```
## 5. Keep Init Light
```python
# GOOD - Lazy initialization
_table = None
def get_table():
global _table
if _table is None:
dynamodb = boto3.resource('dynamodb')
_table = dynamodb.Table(os.environ['TABLE_NAME'])
return _table
def handler(event, context):
table = get_table() # Only initializes on first use
# ...
```
### Optimization_priority
- 1: Reduce package size (biggest impact)
- 2: Use SnapStart for Java/.NET
- 3: Increase memory for faster init
- 4: Delay heavy imports
- 5: Provisioned concurrency (last resort)
### SAM Local Development Pattern
Local testing and debugging with SAM CLI
**When to use**: Local development and testing,Debugging Lambda functions,Testing API Gateway locally
```bash
# Install SAM CLI
pip install aws-sam-cli
# Initialize new project
sam init --runtime nodejs20.x --name my-api
# Build the project
sam build
# Run locally
sam local start-api
# Invoke single function
sam local invoke GetItemFunction --event events/get.json
# Local debugging (Node.js with VS Code)
sam local invoke --debug-port 5858 GetItemFunction
# Deploy
sam deploy --guided
```
```json
// events/get.json (test event)
{
"pathParameters": {
"id": "123"
},
"httpMethod": "GET",
"path": "/items/123"
}
```
```json
// .vscode/launch.json (for debugging)
{
"version": "0.2.0",
"configurations": [
{
"name": "Attach to SAM CLI",
"type": "node",
"request": "attach",
"address": "localhost",
"port": 5858,
"localRoot": "${workspaceRoot}/src",
"remoteRoot": "/var/task/src",
"protocol": "inspector"
}
]
}
```
### Commands
- Sam_build: Build Lambda deployment packages
- Sam_local_start_api: Start local API Gateway
- Sam_local_invoke: Invoke single function
- Sam_deploy: Deploy to AWS
- Sam_logs: Tail CloudWatch logs
### CDK Serverless Pattern
Infrastructure as code with AWS CDK
**When to use**: Complex infrastructure beyond Lambda,Prefer programming languages over YAML,Need reusable constructs
```typescript
// lib/api-stack.ts
import * as cdk from 'aws-cdk-lib';
import * as lambda from 'aws-cdk-lib/aws-lambda';
import * as apigateway from 'aws-cdk-lib/aws-apigateway';
import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
import { Construct } from 'constructs';
export class ApiStack extends cdk.Stack {
constructor(scope: Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);
// DynamoDB Table
const table = new dynamodb.Table(this, 'ItemsTable', {
partitionKey: { name: 'id', type: dynamodb.AttributeType.STRING },
billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
removalPolicy: cdk.RemovalPolicy.DESTROY, // For dev only
});
// Lambda Function
const getItemFn = new lambda.Function(this, 'GetItemFunction', {
runtime: lambda.Runtime.NODEJS_20_X,
handler: 'get.handler',
code: lambda.Code.fromAsset('src/handlers'),
environment: {
TABLE_NAME: table.tableName,
},
memorySize: 256,
timeout: cdk.Duration.seconds(30),
});
// Grant permissions
table.grantReadData(getItemFn);
// API Gateway
const api = new apigateway.RestApi(this, 'ItemsApi', {
restApiName: 'Items Service',
defaultCorsPreflightOptions: {
allowOrigins: apigateway.Cors.ALL_ORIGINS,
allowMethods: apigateway.Cors.ALL_METHODS,
},
});
const items = api.root.addResource('items');
const item = items.addResource('{id}');
item.addMethod('GET', new apigateway.LambdaIntegration(getItemFn));
// Output API URL
new cdk.CfnOutput(this, 'ApiUrl', {
value: api.url,
});
}
}
```
```bash
# CDK commands
npm install -g aws-cdk
cdk init app --language typescript
cdk synth # Generate CloudFormation
cdk diff # Show changes
cdk deploy # Deploy to AWS
```
## Sharp Edges
### Cold Start INIT Phase Now Billed (Aug 2025)
Severity: HIGH
Situation: Running Lambda functions in production
Symptoms:
Unexplained increase in Lambda costs (10-50% higher).
Bill includes charges for function initialization.
Functions with heavy startup logic cost more than expected.
Why this breaks:
As of August 1, 2025, AWS bills the INIT phase the same way it bills
invocation duration. Previously, cold start initialization wasn't billed
for the full duration.
This affects functions with:
- Heavy dependency loading (large packages)
- Slow initialization code
- Frequent cold starts (low traffic or poor concurrency)
Cold starts now directly impact your bill, not just latency.
Recommended fix:
## Measure your INIT phase
```bash
# Check CloudWatch Logs for INIT_REPORT
# Look for Init Duration in milliseconds
# Example log line:
# INIT_REPORT Init Duration: 423.45 ms
```
## Reduce INIT duration
```javascript
// 1. Minimize package size
// Use tree shaking, exclude dev dependencies
// npm prune --production
// 2. Lazy load heavy dependencies
let heavyLib = null;
function getHeavyLib() {
if (!heavyLib) {
heavyLib = require('heavy-library');
}
return heavyLib;
}
// 3. Use AWS SDK v3 modular imports
const { S3Client } = require('@aws-sdk/client-s3');
// NOT: const AWS = require('aws-sdk');
```
## Use SnapStart for Java/.NET
```yaml
Resources:
JavaFunction:
Type: AWS::Serverless::Function
Properties:
Runtime: java21
SnapStart:
ApplyOn: PublishedVersions
```
## Monitor cold start frequency
```javascript
// Track cold starts with custom metric
let isColdStart = true;
exports.handler = async (event) => {
if (isColdStart) {
console.log('COLD_START');
// CloudWatch custom metric here
isColdStart = false;
}
// ...
};
```
### Lambda Timeout Misconfiguration
Severity: HIGH
Situation: Running Lambda functions, especially with external calls
Symptoms:
Function times out unexpectedly.
"Task timed out after X seconds" in logs.
Partial processing with no response.
Silent failures with no error caught.
Why this breaks:
Default Lambda timeout is only 3 seconds. Maximum is 15 minutes.
Common timeout causes:
- Default timeout too short for workload
- Downstream service taking longer than expected
- Network issues in VPC
- Infinite loops or blocking operations
- S3 downloads larger than expected
Lambda terminates at timeout without graceful shutdown.
Recommended fix:
## Set appropriate timeout
```yaml
# template.yaml
Resources:
MyFunction:
Type: AWS::Serverless::Function
Properties:
Timeout: 30 # Seconds (max 900)
# Set to expected duration + buffer
```
## Implement timeout awareness
```javascript
exports.handler = async (event, context) => {
// Get remaining time
const remainingTime = context.getRemainingTimeInMillis();
// If running low on time, fail gracefully
if (remainingTime < 5000) {
console.warn('Running low on time, aborting');
throw new Error('Insufficient time remaining');
}
// For long operations, check periodically
for (const item of items) {
if (context.getRemainingTimeInMillis() < 10000) {
// Save progress and exit gracefully
await saveProgress(processedItems);
throw new Error('Timeout approaching, saved progress');
}
await processItem(item);
}
};
```
## Set downstream timeouts
```javascript
const axios = require('axios');
// Always set timeouts on HTTP calls
const response = await axios.get('https://api.example.com/data', {
timeout: 5000 // 5 seconds
});
```
### Out of Memory (OOM) Crash
Severity: HIGH
Situation: Lambda function processing data
Symptoms:
Function stops abruptly without error.
CloudWatch logs appear truncated.
"Max Memory Used" hits configured limit.
Inconsistent behavior under load.
Why this breaks:
When Lambda exceeds memory allocation, AWS forcibly terminates
the runtime. This happens without raising a catchable exception.
Common causes:
- Processing large files in memory
- Memory leaks across invocations
- Buffering entire response bodies
- Heavy libraries consuming too much memory
Recommended fix:
## Increase memory allocation
```yaml
Resources:
MyFunction:
Type: AWS::Serverless::Function
Properties:
MemorySize: 1024 # MB (128-10240)
# More memory = more CPU too
```
## Stream large data
```javascript
// BAD - loads entire file into memory
const data = await s3.getObject(params).promise();
const content = data.Body.toString();
// GOOD - stream processing
const { S3Client, GetObjectCommand } = require('@aws-sdk/client-s3');
const s3 = new S3Client({});
const response = await s3.send(new GetObjectCommand(params));
const stream = response.Body;
// Process stream in chunks
for await (const chunk of stream) {
await processChunk(chunk);
}
```
## Monitor memory usage
```javascript
exports.handler = async (event, context) => {
const used = process.memoryUsage();
console.log('Memory:', {
heapUsed: Math.round(used.heapUsed / 1024 / 1024) + 'MB',
heapTotal: Math.round(used.heapTotal / 1024 / 1024) + 'MB'
});
// ...
};
```
## Use Lambda Power Tuning
```bash
# Find optimal memory setting
# https://github.com/alexcasalboni/aws-lambda-power-tuning
```
### VPC-Attached Lambda Cold Start Delay
Severity: MEDIUM
Situation: Lambda functions in VPC accessing private resources
Symptoms:
Extremely slow cold starts (was 10+ seconds, now ~100ms).
Timeouts on first invocation after idle period.
Functions work in VPC but slow compared to non-VPC.
Why this breaks:
Lambda functions in VPC need Elastic Network Interfaces (ENIs).
AWS improved this significantly with Hyperplane ENIs, but:
- First cold start in VPC still has overhead
- NAT Gateway issues can cause timeouts
- Security group misconfig blocks traffic
- DNS resolution can be slow
Recommended fix:
## Verify VPC configuration
```yaml
Resources:
MyFunction:
Type: AWS::Serverless::Function
Properties:
VpcConfig:
SecurityGroupIds:
- !Ref LambdaSecurityGroup
SubnetIds:
- !Ref PrivateSubnet1
- !Ref PrivateSubnet2 # Multiple AZs
LambdaSecurityGroup:
Type: AWS::EC2::SecurityGroup
Properties:
GroupDescription: Lambda SG
VpcId: !Ref VPC
SecurityGroupEgress:
- IpProtocol: tcp
FromPort: 443
ToPort: 443
CidrIp: 0.0.0.0/0 # Allow HTTPS outbound
```
## Use VPC endpoints for AWS services
```yaml
# Avoid NAT Gateway for AWS service calls
DynamoDBEndpoint:
Type: AWS::EC2::VPCEndpoint
Properties:
ServiceName: !Sub com.amazonaws.${AWS::Region}.dynamodb
VpcId: !Ref VPC
RouteTableIds:
- !Ref PrivateRouteTable
VpcEndpointType: Gateway
S3Endpoint:
Type: AWS::EC2::VPCEndpoint
Properties:
ServiceName: !Sub com.amazonaws.${AWS::Region}.s3
VpcId: !Ref VPC
VpcEndpointType: Gateway
```
## Only use VPC when necessary
Don't attach Lambda to VPC unless you need:
- Access to RDS/ElastiCache in VPC
- Access to private EC2 instances
- Compliance requirements
Most AWS services can be accessed without VPC.
### Node.js Event Loop Not Cleared
Severity: MEDIUM
Situation: Node.js Lambda function with callbacks or timers
Symptoms:
Function takes full timeout duration to return.
"Task timed out" even though logic completed.
Extra billing for idle time.
Why this breaks:
By default, Lambda waits for the Node.js event loop to be empty
before returning. If you have:
- Unresolved setTimeout/setInterval
- Dangling database connections
- Pending callbacks
Lambda waits until timeout, even if your response was ready.
Recommended fix:
## Tell Lambda not to wait for event loop
```javascript
exports.handler = async (event, context) => {
// Don't wait for event loop to clear
context.callbackWaitsForEmptyEventLoop = false;
// Your code here
const result = await processRequest(event);
return {
statusCode: 200,
body: JSON.stringify(result)
};
};
```
## Close connections properly
```javascript
// For database connections, use connection pooling
// or close connections explicitly
const mysql = require('mysql2/promise');
exports.handler = async (event, context) => {
context.callbackWaitsForEmptyEventLoop = false;
const connection = await mysql.createConnection({...});
try {
const [rows] = await connection.query('SELECT * FROM users');
return { statusCode: 200, body: JSON.stringify(rows) };
} finally {
await connection.end(); // Always close
}
};
```
### API Gateway Payload Size Limits
Severity: MEDIUM
Situation: Returning large responses or receiving large requests
Symptoms:
"413 Request Entity Too Large" error
"Execution failed due to configuration error: Malformed Lambda proxy response"
Response truncated or failed
Why this breaks:
API Gateway has hard payload limits:
- REST API: 10 MB request/response
- HTTP API: 10 MB request/response
- Lambda itself: 6 MB sync response, 256 KB async
Exceeding these causes failures that may not be obvious.
Recommended fix:
## For large file uploads
```javascript
// Use presigned S3 URLs instead of passing through API Gateway
const { S3Client, PutObjectCommand } = require('@aws-sdk/client-s3');
const { getSignedUrl } = require('@aws-sdk/s3-request-presigner');
exports.handler = async (event) => {
const s3 = new S3Client({});
const command = new PutObjectCommand({
Bucket: process.env.BUCKET_NAME,
Key: `uploads/${Date.now()}.file`
});
const uploadUrl = await getSignedUrl(s3, command, { expiresIn: 300 });
return {
statusCode: 200,
body: JSON.stringify({ uploadUrl })
};
};
```
## For large responses
```javascript
// Store in S3, return presigned download URL
exports.handler = async (event) => {
const largeData = await generateLargeReport();
await s3.send(new PutObjectCommand({
Bucket: process.env.BUCKET_NAME,
Key: `reports/${reportId}.json`,
Body: JSON.stringify(largeData)
}));
const downloadUrl = await getSignedUrl(s3,
new GetObjectCommand({
Bucket: process.env.BUCKET_NAME,
Key: `reports/${reportId}.json`
}),
{ expiresIn: 3600 }
);
return {
statusCode: 200,
body: JSON.stringify({ downloadUrl })
};
};
```
### Infinite Loop or Recursive Invocation
Severity: HIGH
Situation: Lambda triggered by events
Symptoms:
Runaway costs.
Thousands of invocations in minutes.
CloudWatch logs show repeated invocations.
Lambda writing to source bucket/table that triggers it.
Why this breaks:
Lambda can accidentally trigger itself:
- S3 trigger writes back to same bucket
- DynamoDB trigger updates same table
- SNS publishes to topic that triggers it
- Step Functions with wrong error handling
Recommended fix:
## Use different buckets/prefixes
```yaml
# S3 trigger with prefix filter
Events:
S3Event:
Type: S3
Properties:
Bucket: !Ref InputBucket
Events: s3:ObjectCreated:*
Filter:
S3Key:
Rules:
- Name: prefix
Value: uploads/ # Only trigger on uploads/
# Output to different bucket or prefix
# OutputBucket or processed/ prefix
```
## Add idempotency checks
```javascript
exports.handler = async (event) => {
for (const record of event.Records) {
const key = record.s3.object.key;
// Skip if this is a processed file
if (key.startsWith('processed/')) {
console.log('Skipping already processed file:', key);
continue;
}
// Process and write to different location
await processFile(key);
await writeToS3(`processed/${key}`, result);
}
};
```
## Set reserved concurrency as circuit breaker
```yaml
Resources:
RiskyFunction:
Type: AWS::Serverless::Function
Properties:
ReservedConcurrentExecutions: 10 # Max 10 parallel
# Limits blast radius of runaway invocations
```
## Monitor with CloudWatch alarms
```yaml
InvocationAlarm:
Type: AWS::CloudWatch::Alarm
Properties:
MetricName: Invocations
Namespace: AWS/Lambda
Statistic: Sum
Period: 60
EvaluationPeriods: 1
Threshold: 1000 # Alert if >1000 invocations/min
ComparisonOperator: GreaterThanThreshold
```
## Validation Checks
### Hardcoded AWS Credentials
Severity: ERROR
AWS credentials must never be hardcoded
Message: Hardcoded AWS access key detected. Use IAM roles or environment variables.
### AWS Secret Key in Source Code
Severity: ERROR
Secret keys should use Secrets Manager or environment variables
Message: Hardcoded AWS secret key. Use IAM roles or Secrets Manager.
### Overly Permissive IAM Policy
Severity: WARNING
Avoid wildcard permissions in Lambda IAM roles
Message: Overly permissive IAM policy. Use least privilege principle.
### Lambda Handler Without Error Handling
Severity: WARNING
Lambda handlers should have try/catch for graceful errors
Message: Lambda handler without error handling. Add try/catch.
### Missing callbackWaitsForEmptyEventLoop
Severity: INFO
Node.js handlers should set callbackWaitsForEmptyEventLoop
Message: Consider setting context.callbackWaitsForEmptyEventLoop = false
### Default Memory Configuration
Severity: INFO
Default 128MB may be too low for many workloads
Message: Using default 128MB memory. Consider increasing for better performance.
### Low Timeout Configuration
Severity: WARNING
Very low timeout may cause unexpected failures
Message: Timeout of 1-3 seconds may be too low. Increase if making external calls.
### No Dead Letter Queue Configuration
Severity: WARNING
Async functions should have DLQ for failed invocations
Message: No DLQ configured. Add for async invocations.
### Importing Full AWS SDK v2
Severity: WARNING
Import specific clients from AWS SDK v3 for smaller packages
Message: Importing full AWS SDK. Use modular SDK v3 imports for smaller packages.
### Hardcoded DynamoDB Table Name
Severity: WARNING
Table names should come from environment variables
Message: Hardcoded table name. Use environment variable for portability.
## Collaboration
### Delegation Triggers
- user needs GCP serverless -> gcp-cloud-run (Cloud Run for containers, Cloud Functions for events)
- user needs Azure serverless -> azure-functions (Azure Functions, Logic Apps)
- user needs database design -> postgres-wizard (RDS design, or use DynamoDB patterns)
- user needs authentication -> auth-specialist (Cognito, API Gateway authorizers)
- user needs complex workflows -> workflow-automation (Step Functions, EventBridge)
- user needs AI integration -> llm-architect (Lambda calling Bedrock or external LLMs)
## When to Use
Use this skill when the request clearly matches the capabilities and patterns described above.
## Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.
© 2026 Flowy · Free and open source
Built for Claude Code · Not affiliated with Anthropic
