MiniStack: Free Local AWS Emulator + Testcontainers Module + AWS CLI Built In

4 releases in a weekend: Testcontainers Java module, AWS CLI bundled, Step Functions intrinsics, RDS Data stubs. Free, open-source, MIT licensed.

TL;DR

We shipped 4 releases this weekend (v1.2.6 through v1.2.9):

org.ministack:testcontainers-ministack:0.1.0 on Maven Central
62 bug fixes found by running 2,490 tests across all 41 services
AWS CLI bundled in the Docker image — init scripts just work
Step Functions intrinsics — 7 new functions (ArrayContains, MathAdd, UUID, etc.)
RDS Data API stubs — test database provisioning without Docker-in-Docker

What is MiniStack?

MiniStack is a free, MIT-licensed local AWS emulator. One Docker image, one port (4566), 41 services. It started as a response to LocalStack moving core services behind a paid plan.

Image size: 269MB (was 242MB before CLI)
Startup time: <2 seconds
Services: S3, DynamoDB, SQS, SNS, Lambda, Step Functions, CloudFormation, EC2, ECS, and 32 more
Docker: ministackorg/ministack
GitHub: ministackorg/ministack

No license keys. No pro tiers. Just run it.

docker run -d -p 4566:4566 ministackorg/ministack

Testcontainers Module

<dependency>
    <groupId>org.ministack</groupId>
    <artifactId>testcontainers-ministack</artifactId>
    <version>0.1.0</version>
    <scope>test</scope>
</dependency>

@Testcontainers
class S3IntegrationTest {

    @Container
    static MiniStackContainer ministack = new MiniStackContainer("ministackorg/ministack:latest");

    @Test
    void shouldCreateBucketAndPutObject() {
        S3Client s3 = S3Client.builder()
                .endpointOverride(ministack.getEndpoint())
                .credentialsProvider(ministack.getCredentialsProvider())
                .region(Region.US_EAST_1)
                .build();

        s3.createBucket(b -> b.bucket("test-bucket"));
        s3.putObject(
                b -> b.bucket("test-bucket").key("hello.txt"),
                RequestBody.fromString("Hello MiniStack!")
        );

        String body = s3.getObjectAsBytes(
                b -> b.bucket("test-bucket").key("hello.txt")
        ).asUtf8String();

        assertEquals("Hello MiniStack!", body);
    }
}

Works with JUnit 5 and Spring Boot's @DynamicPropertySource. The container starts in under 2 seconds.

AWS CLI Bundled (v1.2.9)

The Docker image now ships with AWS CLI v1. Init scripts just work without any credential configuration:

# ready.d/01-create-resources.sh
aws s3 mb s3://my-bucket
aws sqs create-queue --queue-name my-queue

# ready.d/02-seed-data.py
import boto3, os
s3 = boto3.client("s3", endpoint_url=os.environ["AWS_ENDPOINT_URL"])
s3.put_object(Bucket="my-bucket", Key="config.json", Body=b'{"env": "local"}')

Both .sh and .py init scripts are supported. AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_DEFAULT_REGION, and AWS_ENDPOINT_URL are automatically set for init scripts.

The Flea Hunt: 62 Bugs Found and Fixed

We ran what we call a "Flea Hunt" — 2,490 tests across all 41 services using 10 parallel MiniStack instances. Some highlights:

S3 versioning — GetObject by VersionId was returning the wrong version. Delete markers were missing entirely from ListObjectVersions.
Lambda — internal _request_id was leaking into handler events. PublishVersion ARN was missing the :version qualifier.
DynamoDB — Go SDK v2 requires a CRC32 header on every response. Without it, the SDK throws an integrity error before your code sees anything.
Java SDK v2 — time.time() floats in scientific notation broke the timestamp parser across 14 services. Fixed with int(time.time()).
EC2 — TagSpecifications were silently ignored on 11 create operations. DeleteVpc succeeded even with subnets attached.

After the fixes: 1,327 regression tests (1,196 Python + 131 Java), zero failures.

Quick Start

Docker:

docker run -d -p 4566:4566 ministackorg/ministack

Terraform:

provider "aws" {
  endpoints {
    s3       = "http://localhost:4566"
    dynamodb = "http://localhost:4566"
    sqs      = "http://localhost:4566"
  }
  region     = "us-east-1"
  access_key = "test"
  secret_key = "test"
}