MildStack: Free Open Source LocalStack Alternative

MildStack provides SQS emulation with standard and FIFO queues, dead-letter queues, message move tasks, and full message lifecycle support.

Overview

MildStack's SQS emulation lets you create queues, send and receive messages, and configure dead-letter queues locally. It supports both standard and FIFO queues, and is fully compatible with the AWS SQS API.

Supported Operations

Queue Lifecycle

Operation	Description
`CreateQueue`	Create a new standard or FIFO queue
`DeleteQueue`	Delete a queue and all its messages
`GetQueueUrl`	Get the URL of a queue by name
`ListQueues`	List all queues
`PurgeQueue`	Delete all messages in a queue
`GetQueueAttributes`	Get queue configuration (visibility timeout, DLQ, etc.)
`SetQueueAttributes`	Update queue configuration

Message Operations

Operation	Description
`SendMessage`	Send a single message to a queue
`SendMessageBatch`	Send up to 10 messages in a single request
`ReceiveMessage`	Receive one or more messages from a queue
`DeleteMessage`	Delete a processed message
`DeleteMessageBatch`	Delete multiple messages at once
`ChangeMessageVisibility`	Extend or shorten the visibility timeout of a message
`ChangeMessageVisibilityBatch`	Update visibility for multiple messages

Queue Tags & Permissions

Operation	Description
`TagQueue`	Add tags to a queue
`UntagQueue`	Remove tags from a queue
`ListQueueTags`	List all tags on a queue
`AddPermission`	Add a permission to a queue policy
`RemovePermission`	Remove a permission from a queue policy

Dead-Letter Queue (DLQ) & Redrive

Operation	Description
`ListDeadLetterSourceQueues`	List queues that use a specific DLQ
`StartMessageMoveTask`	Start moving messages from a DLQ back to the source queue
`CancelMessageMoveTask`	Cancel a running message move task
`ListMessageMoveTasks`	List active and completed move tasks

Quick Example

import {
  SQSClient,
  CreateQueueCommand,
  SendMessageCommand,
  ReceiveMessageCommand,
  DeleteMessageCommand,
} from "@aws-sdk/client-sqs";

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

// Create a queue
const { QueueUrl } = await sqs.send(
  new CreateQueueCommand({ QueueName: "tasks" })
);

// Send a message
await sqs.send(
  new SendMessageCommand({
    QueueUrl,
    MessageBody: JSON.stringify({
      action: "process-image",
      imageId: "img-456",
    }),
  })
);

// Receive messages
const { Messages } = await sqs.send(
  new ReceiveMessageCommand({
    QueueUrl,
    MaxNumberOfMessages: 10,
    WaitTimeSeconds: 5,
  })
);

// Process and delete
if (Messages) {
  for (const message of Messages) {
    console.log("Received:", message.Body);
    await sqs.send(
      new DeleteMessageCommand({
        QueueUrl,
        ReceiptHandle: message.ReceiptHandle,
      })
    );
  }
}

Dead-Letter Queue Example

Configure a DLQ to capture messages that fail processing:

// Create the DLQ
const { QueueUrl: dlqUrl } = await sqs.send(
  new CreateQueueCommand({ QueueName: "tasks-dlq" })
);

// Get the DLQ ARN
const { Attributes } = await sqs.send(
  new GetQueueAttributesCommand({
    QueueUrl: dlqUrl,
    AttributeNames: ["QueueArn"],
  })
);

// Create the main queue with redrive policy
await sqs.send(
  new CreateQueueCommand({
    QueueName: "tasks",
    Attributes: {
      RedrivePolicy: JSON.stringify({
        deadLetterTargetArn: Attributes.QueueArn,
        maxReceiveCount: "3",
      }),
    },
  })
);

After a message has been received 3 times without being deleted, it's automatically moved to the DLQ.

FIFO Queue Example

FIFO queues guarantee ordered, exactly-once delivery:

# Create a FIFO queue
awslocal sqs create-queue \
  --queue-name orders.fifo \
  --attributes FifoQueue=true,ContentBasedDeduplication=true

# Send a message with a group ID
awslocal sqs send-message \
  --queue-url http://localhost:4566/000000000000/orders.fifo \
  --message-body '{"orderId": "order-789"}' \
  --message-group-id "customer-123"

FIFO queue names must end with .fifo. Messages within the same message group are delivered in order.

Queue URL Format

MildStack uses the following URL format for queues:

http://localhost:4566/000000000000/<queue-name>

The account ID 000000000000 is a default placeholder used for local development.

Persistence

All SQS data (queues, messages, DLQ configuration) is stored locally and persists across instance restarts. Deleting an instance removes all its SQS data.

Amazon SQS