aws-cloudformation-lambda

# AWS CloudFormation Lambda Functions

## Overview

Create production-ready Lambda functions using CloudFormation templates with validation and deployment workflows.

## When to Use

- Creating Lambda functions with CloudFormation
- Configuring event sources (S3, SQS, DynamoDB, Kinesis)
- Implementing Lambda layers and cold start optimization
- Integrating Lambda with API Gateway
- Deploying Lambda infrastructure with validation

## Deployment Workflow

Always follow this deployment workflow:

### 1. Validate Template
```bash
aws cloudformation validate-template --template-body file://template.yaml
```

### 2. Deploy Stack
```bash
aws cloudformation deploy \
  --template-file template.yaml \
  --stack-name my-lambda-stack \
  --capabilities CAPABILITY_IAM \
  --parameter-overrides Environment=prod
```

### 3. Monitor Stack Events
```bash
aws cloudformation describe-stack-events \
  --stack-name my-lambda-stack \
  --query 'StackEvents[?ResourceStatus==`CREATE_FAILED`||ResourceStatus==`UPDATE_FAILED`]'
```

### 4. Verify Resources
```bash
aws lambda get-function --function-name my-lambda-stack-function
aws cloudformation describe-stacks --stack-name my-lambda-stack \
  --query 'Stacks[0].StackStatus'
```

### 5. Rollback on Failure
```bash
aws cloudformation delete-stack --stack-name my-lambda-stack
aws logs describe-log-groups --log-group-name-prefix "/aws/lambda/my-lambda"
```

## Instructions

Follow these steps to create Lambda functions with CloudFormation:

### 1. Define Lambda Function Parameters

Specify runtime, memory, timeout, and environment variables:

```yaml
Parameters:
  FunctionMemory:
    Type: Number
    Default: 256
    AllowedValues:
      - 128
      - 256
      - 512
      - 1024
      - 2048
    Description: Lambda function memory in MB

  FunctionTimeout:
    Type: Number
    Default: 30
    MinValue: 1
    MaxValue: 900
    Description: Function timeout in seconds

  Runtime:
    Type: String
    Default: nodejs20.x
    AllowedValues:
      - nodejs20.x
      - python3.11
      - java21
      - dotnet8
      - go1.x
    Description: Lambda runtime environment
```

### 2. Create Lambda Function

Define the basic function configuration:

```yaml
Resources:
  LambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: !Sub "${AWS::StackName}-function"
      Runtime: !Ref Runtime
      Handler: index.handler
      Role: !Ref ExecutionRole
      MemorySize: !Ref FunctionMemory
      Timeout: !Ref FunctionTimeout
      Code:
        S3Bucket: !Ref CodeBucket
        S3Key: !Ref CodeKey
      Environment:
        Variables:
          LOG_LEVEL: INFO
          DATABASE_URL: !Ref DatabaseUrl
      Tags:
        - Key: Environment
          Value: !Ref Environment
```

### 3. Configure Execution Role

Apply least privilege IAM policies:

```yaml
Resources:
  ExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: S3ReadAccess
          PolicyDocument:
            Version: "2012-10-17"
            Statement:
              - Effect: Allow
                Action:
                  - s3:GetObject
                Resource: !Sub "${DataBucket.Arn}/*"
```

### 4. Add Event Sources

Configure triggers for Lambda invocation:

```yaml
Resources:
  # S3 event source
  S3EventSource:
    Type: AWS::Lambda::EventSourceMapping
    Properties:
      EventSourceArn: !GetAtt DataBucket.Arn
      FunctionName: !Ref LambdaFunction

  # SQS event source
  SQSEventSource:
    Type: AWS::Lambda::EventSourceMapping
    Properties:
      EventSourceArn: !GetAtt Queue.Arn
      FunctionName: !Ref LambdaFunction
      BatchSize: 10
      MaximumBatchingWindowInSeconds: 5
```

### 5. Configure API Gateway Integration

Set up REST or HTTP API integration:

```yaml
Resources:
  # HTTP API integration
  HttpApi:
    Type: AWS::ApiGatewayV2::Api
    Properties:
      Name: !Sub "${AWS::StackName}-api"
      ProtocolType: HTTP
      Target: !Ref LambdaFunction

  ApiIntegration:
    Type: AWS::ApiGatewayV2::Integration
    Properties:
      ApiId: !Ref HttpApi
      IntegrationType: AWS_PROXY
      IntegrationUri: !Sub "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${LambdaFunction.Arn}/invocations"
```

### 6. Implement Versioning and Aliases

Create function versions and aliases:

```yaml
Resources:
  LambdaVersion:
    Type: AWS::Lambda::Version
    Properties:
      FunctionName: !Ref LambdaFunction
      Description: !Sub "Version ${AWS::StackName} v1"

  LambdaAlias:
    Type: AWS::Lambda::Alias
    Properties:
      FunctionName: !Ref LambdaFunction
      FunctionVersion: !GetAtt LambdaVersion.Version
      Name: live
```

### 7. Configure Monitoring

Enable CloudWatch logging and X-Ray tracing:

```yaml
Resources:
  LambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      LoggingConfig:
        LogGroup: !Ref LogGroup
      TracingConfig:
        Mode: Active

  LogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Sub "/aws/lambda/${LambdaFunction}"
      RetentionInDays: 7
```

### 8. Set Up Dead Letter Queue

Configure DLQ for failed invocations:

```yaml
Resources:
  DeadLetterQueue:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: !Sub "${AWS::StackName}-dlq"

  LambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      DeadLetterConfig:
        TargetArn: !GetAtt DeadLetterQueue.Arn
```

## Examples

### Complete Lambda Stack Template

```yaml
AWSTemplateFormatVersion: '2010-09-09'
Description: Lambda function with monitoring and DLQ

Parameters:
  FunctionMemory:
    Type: Number
    Default: 256
    AllowedValues: [128, 256, 512, 1024]
  FunctionT