cognito-local 0.1.0

A lightweight, persistent Cognito mock server using Moto with file-based state persistence.

cognito-local

A lightweight, persistent Cognito mock server using Moto with file-based state persistence.

This is a wrapper around the moto library in a lightweight Docker container and adds a custom persistence layer that auto-saves your data to disk.

✨ Features

💾 Persistent. ⚡ Blazing Fast. 🆓 Free & Open. 🐳 Docker Ready.

Cryptography Support: Includes patches to correctly serialize RSA keys used for JWT signing.

🔁 Auto-Save: Background thread saves state every interval and handles graceful shutdowns (SIGTERM).

It supports multiple regions and can be configured to use a custom data directory.

🚀 Quick Start

Using Docker Compose (Recommended)

Add this to your docker-compose.yml.

services:
  cognito:
    image: usermalikhan/cognito-local:latest
    container_name: cognito-local
    ports:
      - "4566:4566"
    volumes:
      - ./cognito-data:/data
    environment:
      - AWS_DEFAULT_REGION=eu-central-1
      - PORT=4566

Using Docker CLI

docker run -d \
  -p 4566:4566 \
  -v $(pwd)/cognito-data:/data \
  --region eu-central-1 \
  --name cognito-local \
  usermalikhan/cognito-local:latest

🛠 How It Works

This project is a Python wrapper around the moto[server] library.

The Engine: It uses moto's ThreadedMotoServer to handle AWS API requests.

The Patch: It injects a custom serializer into Python's pickle module using copyreg. This allows it to save complex C-based cryptography objects (like RSA Private Keys) which standard Python cannot pickle.

The Loop: A background thread monitors the Moto backend object. Every interval (or on Docker shutdown signals), it dumps the entire memory state to a file (/data/cognito.db).

The Restoration: On startup, it checks for the database file and injects the data back into Moto's memory before the server starts accepting requests.

🔌 Connecting to It

Since this is a local mock, you must tell your AWS clients (CLI, Boto3, JS SDK) to use the local endpoint.

Note: You must specify a region and fake credentials.

AWS CLI

1. Configure fake credentials for the session

export AWS_ACCESS_KEY_ID=test
export AWS_SECRET_ACCESS_KEY=test
export AWS_DEFAULT_REGION=eu-central-1

2. Run commands pointing to localhost

aws --endpoint-url=http://localhost:4566 cognito-idp create-user-pool --pool-name "MyPersistentPool"

Python (Boto3)

import boto3

cognito = boto3.client(
    "cognito-idp",
    region_name="eu-central-1",
    endpoint_url="http://localhost:4566",
    aws_access_key_id="test",
    aws_secret_access_key="test"
)
cognito.create_user_pool(PoolName="MyTestPool")

JavaScript / TypeScript (AWS SDK v3)

import { CognitoIdentityProviderClient } from "@aws-sdk/client-cognito-identity-provider";

const client = new CognitoIdentityProviderClient({
  region: "eu-central-1",
  endpoint: "http://localhost:4566",
  credentials: {
    accessKeyId: "test",
    secretAccessKey: "test",
  },
});

⚙️ Configuration

You can configure the behavior using Environment Variables in Docker:

Variable	Default	Description
PORT	4566	The port the server listens on.
DATA_FILE	/data/cognito.db	Path inside the container where data is saved.
SAVE_INTERVAL	60	How often (in seconds) to auto-save to disk.

🧪 Development

If you want to contribute or run this locally without Docker:

1. Clone repo

git clone https://github.com/m-ali-ubit/cognito-local.git
cd cognito-local

2. Install dependencies

pip install -e .[dev]

3. Run Server

python -m cognito_local.main

4. Run Tests

pytest

⚖️ License

Apache License 2.0

This project is not affiliated with AWS or LocalStack. It is an independent open-source tool based on the Moto library.