MildStack: Free Open Source LocalStack Alternative

MildStack provides DynamoDB emulation with table management, item operations, queries, scans, secondary indexes, and batch/transaction support.

Overview

MildStack's DynamoDB emulation lets you create tables, store items, and perform queries locally. It supports the standard DynamoDB JSON wire protocol, so your existing AWS SDK code works without changes — just update the endpoint URL.

Supported Operations

Table Operations

Operation	Description
`CreateTable`	Create a new table with key schema and optional indexes
`DescribeTable`	Get table details (status, key schema, indexes, item count)
`ListTables`	List all tables
`DeleteTable`	Delete a table and all its items

Item Operations

Operation	Description
`PutItem`	Create or replace an item
`GetItem`	Retrieve a single item by key
`UpdateItem`	Update specific attributes of an item
`DeleteItem`	Delete a single item by key

Query & Scan

Operation	Description
`Query`	Query items by partition key with optional sort key conditions
`Scan`	Scan all items in a table with optional filters

Batch & Transactions

Operation	Description
`BatchGetItem`	Get multiple items across tables in a single request
`BatchWriteItem`	Put or delete multiple items across tables in a single request
`TransactGetItems`	Read multiple items atomically
`TransactWriteItems`	Write multiple items atomically

Time to Live (TTL)

Operation	Description
`UpdateTimeToLive`	Enable or disable TTL on a table
`DescribeTimeToLive`	Get the current TTL configuration

Secondary Indexes

MildStack supports both types of secondary indexes:

Global Secondary Indexes (GSI) — Query items by any attribute, across all partitions
Local Secondary Indexes (LSI) — Query items by an alternative sort key within a partition

Quick Example

import {
  DynamoDBClient,
  CreateTableCommand,
  PutItemCommand,
  QueryCommand,
} from "@aws-sdk/client-dynamodb";

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

// Create a table
await client.send(
  new CreateTableCommand({
    TableName: "Orders",
    KeySchema: [
      { AttributeName: "customerId", KeyType: "HASH" },
      { AttributeName: "orderId", KeyType: "RANGE" },
    ],
    AttributeDefinitions: [
      { AttributeName: "customerId", AttributeType: "S" },
      { AttributeName: "orderId", AttributeType: "S" },
    ],
    BillingMode: "PAY_PER_REQUEST",
  })
);

// Put an item
await client.send(
  new PutItemCommand({
    TableName: "Orders",
    Item: {
      customerId: { S: "cust-123" },
      orderId: { S: "order-001" },
      total: { N: "59.99" },
      status: { S: "shipped" },
    },
  })
);

// Query items for a customer
const result = await client.send(
  new QueryCommand({
    TableName: "Orders",
    KeyConditionExpression: "customerId = :cid",
    ExpressionAttributeValues: {
      ":cid": { S: "cust-123" },
    },
  })
);
console.log(result.Items);

AWS CLI Examples

# Create a table with a GSI
awslocal dynamodb create-table \
  --table-name Products \
  --attribute-definitions \
    AttributeName=id,AttributeType=S \
    AttributeName=category,AttributeType=S \
  --key-schema AttributeName=id,KeyType=HASH \
  --global-secondary-indexes \
    '[{
      "IndexName": "CategoryIndex",
      "KeySchema": [{"AttributeName": "category", "KeyType": "HASH"}],
      "Projection": {"ProjectionType": "ALL"}
    }]' \
  --billing-mode PAY_PER_REQUEST

# Put an item
awslocal dynamodb put-item \
  --table-name Products \
  --item '{
    "id": {"S": "prod-1"},
    "category": {"S": "electronics"},
    "name": {"S": "Wireless Mouse"},
    "price": {"N": "29.99"}
  }'

# Query by GSI
awslocal dynamodb query \
  --table-name Products \
  --index-name CategoryIndex \
  --key-condition-expression "category = :cat" \
  --expression-attribute-values '{":cat": {"S": "electronics"}}'

# Scan with filter
awslocal dynamodb scan \
  --table-name Products \
  --filter-expression "price < :maxPrice" \
  --expression-attribute-values '{":maxPrice": {"N": "50"}}'

Supported Data Types

MildStack supports all DynamoDB attribute types:

Type	Code	Example
String	`S`	`{"S": "hello"}`
Number	`N`	`{"N": "42"}`
Boolean	`BOOL`	`{"BOOL": true}`
Null	`NULL`	`{"NULL": true}`
Map	`M`	`{"M": {"key": {"S": "value"}}}`
List	`L`	`{"L": [{"S": "a"}, {"N": "1"}]}`

Persistence

All DynamoDB data is stored in a local database on your machine. Tables, items, and index data persist across instance restarts. Deleting an instance removes all its DynamoDB data.

Amazon DynamoDB