Lambda

Overview

CloudMock emulates AWS Lambda function management (create, update, delete, list, invoke). Function invocation returns a stub 200 response — actual code execution is not performed.

Supported Operations

Operation	Status	Notes
CreateFunction	Supported	Stores function configuration and code reference
DeleteFunction	Supported	Removes a function
GetFunction	Supported	Returns function configuration
ListFunctions	Supported	Returns all functions
UpdateFunctionCode	Supported	Updates the code reference
UpdateFunctionConfiguration	Supported	Updates runtime, handler, environment, etc.
InvokeFunction	Supported	Returns a stub 200 response; does not execute code
AddPermission	Supported	Stores a resource-based policy statement
RemovePermission	Supported	Removes a policy statement
CreateEventSourceMapping	Supported	Stores an event source mapping
ListEventSourceMappings	Supported	Returns all event source mappings
TagResource	Supported	Adds tags to a function
UntagResource	Supported	Removes tags from a function

Quick Start

curl

# Create a function
curl -X POST http://localhost:4566/2015-03-31/functions \
  -H "Content-Type: application/json" \
  -d '{
    "FunctionName": "my-function",
    "Runtime": "nodejs20.x",
    "Role": "arn:aws:iam::000000000000:role/lambda-role",
    "Handler": "index.handler",
    "Code": {"ZipFile": "UEsDBBQAAAAI..."}
  }'

# Invoke (stub response)
curl -X POST http://localhost:4566/2015-03-31/functions/my-function/invocations \
  -d '{"key": "value"}'

Node.js

import { LambdaClient, CreateFunctionCommand, InvokeCommand } from '@aws-sdk/client-lambda';

const lambda = new LambdaClient({
  endpoint: 'http://localhost:4566',
  region: 'us-east-1',
  credentials: { accessKeyId: 'test', secretAccessKey: 'test' },
});

await lambda.send(new CreateFunctionCommand({
  FunctionName: 'hello',
  Runtime: 'nodejs20.x',
  Role: 'arn:aws:iam::000000000000:role/lambda-role',
  Handler: 'index.handler',
  Code: { ZipFile: Buffer.from('placeholder') },
}));

const response = await lambda.send(new InvokeCommand({
  FunctionName: 'hello', Payload: Buffer.from('{}'),
}));

Python

import boto3, zipfile, io

client = boto3.client('lambda', endpoint_url='http://localhost:4566',
                      aws_access_key_id='test', aws_secret_access_key='test',
                      region_name='us-east-1')

buf = io.BytesIO()
with zipfile.ZipFile(buf, 'w') as zf:
    zf.writestr('index.js', 'exports.handler = async () => ({ statusCode: 200 });')
buf.seek(0)

client.create_function(
    FunctionName='hello', Runtime='nodejs20.x',
    Role='arn:aws:iam::000000000000:role/lambda-role',
    Handler='index.handler', Code={'ZipFile': buf.read()},
)

response = client.invoke(FunctionName='hello', Payload=b'{}')
print(response['StatusCode'])  # 200

Configuration

cloudmock.yml

services:
  lambda:
    enabled: true

No additional service-specific configuration is required.

Known Differences from AWS

• Invocation is a stub — InvokeFunction returns an empty 200 response without executing any code.
• Event source mappings are stored and returned but no trigger logic runs.
• Layers, versions, and aliases are not implemented.
• Concurrency limits are not enforced.
• To test Lambda-triggered workflows, invoke your function logic directly in your test code and use CloudMock for the downstream services (SQS, DynamoDB, S3, etc.).

Error Codes

Code	HTTP Status	Description
ResourceNotFoundException	404	The specified function does not exist
ResourceConflictException	409	A function with this name already exists
InvalidParameterValueException	400	A parameter value is not valid
ServiceException	500	Internal service error