Announcing LocalStack 4.0 General Availability!

Introduction

We are thrilled to introduce LocalStack 4.0, our latest major release that provides a full-local environment for building and testing cloud & AI applications, and further extends our advanced and sophisticated developer experience features. LocalStack 4.0 advances our goal to serve as a drop-in replacement for AWS, offering full control over your development environments. As cloud development grows more complex and teams implement hybrid strategies, the demand for effective local development solutions increases. LocalStack 4.0 goes beyond mere emulation, evolving into a holistic developer productivity platform aimed at becoming the go-to solution for cloud development teams globally.

In our last major release, we focused on resiliency, efficiency, and flexibility. With 4.0, we further expand these to include empowerment, acceleration, and transparency. Our goal is to provide efficiency and control to developers and enterprises, along with the freedom to innovate without limits. This allows them to concentrate on building software and achieving results without being affected by restrictive environments that prioritize process over outcome. We also aim to enable development teams to experiment without the concern of cloud waste or operational responsibilities, facilitating scalable workflows that accelerate innovation. Lastly, we strive to demystify cloud applications by opening up the cloud “black box”, making them easier to understand and debug, reducing the need for lengthy processes and security approvals.

This is an exciting leap forward, and we invite you to explore all the new features by upgrading your LocalStack setup or downloading LocalStack 4.0 today!

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How to migrate?

We have many LocalStack 4.0 resources for new and existing users. To upgrade to LocalStack 4.0 using the LocalStack CLI, run the following command to update both the LocalStack Docker image and CLI to the latest version:

$ localstack update all

If using LocalStack with Docker CLI or Docker Compose, update the Docker image by running:

$ docker pull localstack/localstack:4.0.0 # Community Edition
$ docker pull localstack/localstack-pro:4.0.0 # Pro Edition

Pin the LocalStack version in your docker run command or Docker Compose file to 4.0.0.

What’s new in LocalStack 4.0?

Let’s dive into the latest release to uncover its exciting new features and enhancements and see how they can help you get the most out of it!

• Introducing the Bedrock Provider
• Introducing LocalStack Event Studio
• Introducing LocalStack SDK for Python
• New Default EventBridge Provider
• New Default API Gateway Provider
• Unified LocalStack on Kubernetes Support
• New Config Hot Reloading for Lambda Debug Mode
• Improved UX for IAM Policy Stream
• Introducing Stack Overview
• New EventBridge Pipes Resource Browser
• New Cloud Pods Save/Load Features on Web App
• New Ephemeral Instances CLI
• Miscellaneous

Introducing the Bedrock provider

As software increasingly utilizes artificial intelligence (AI), it has become important to be able to build and test these AI capabilities. That’s why we’re incredibly excited that LocalStack 4.0 includes emulation for Amazon Bedrock. This will allow developer to build and test AI-driven applications just like any other AWS service and without worrying about using up their credits. This provider lets users emulate foundation models (FMs) using publicly available Ollama models, helping developers prototype, experiment, and refine AI-powered applications in their local environment. It supports Invoke API, Converse API APIs & Batch processing, with plans to expand features to include streaming, retrieval-augmented generation (RAG), and agents.

The Bedrock provider uses Mistral as the default model, which can be changed with the DEFAULT_BEDROCK_MODEL configuration variable using names from the Ollama library. Models are downloaded on the first invocation. You can set BEDROCK_PREWARM configuration variable to pre-warm the Bedrock engine for automatic model downloading. This emulation facilitates testing AI application workflows, optimizing model use, and ensuring smooth integration before going into production. Our goal is to create an ecosystem where developers can explore AI’s potential with support from LocalStack throughout the development process.

You can find more details on our documentation.

Introducing LocalStack Event Studio

One of LocalStack’s goals is to open the “Black Box” of event-driven systems and enhance the developer experience for event-driven systems, enabling developers to debug, profile, and test events locally. The new LocalStack Event Studio is designed to simplify debugging and invocation of a broad range of AWS event-driven services. Event Studio allows you to see the data exchange between your AWS services, not only are you able to collect all events, but you can also inspect the payload and metadata and are also able to replay events from all of the supported services at key steps.

EventStudio puts you into the driver’s seat and helps to speed up the development and debugging of complex AWS systems. With Event Studio, you can:

• Gain observability to understand the structure flow of events through your system.
• Replay events to debug AWS services consuming the events in your workflow.
• See errors and the necessary information to address them exactly where needed.
• Receive instant feedback on potential misconfigurations of your services.
• Find deep insights into IAM policies and missing permissions.
• Enrich your event contexts and perform advanced flow tracing.

Event Studio supports a range of AWS services including Lambda, EventBridge, SQS, SNS, DynamoDB, and S3, among others. Currently in preview mode, we are working to expand its capabilities with features such as:

• A live pattern/rule matching evaluator against event history.
• A breakpoint debugger for pausing before event dispatch.
• Test event generation integrated with a schema registry.

You can install and utilize Event Studio via the LocalStack Web Application or the CLI by following our documentation. Post installation, you can navigate to eventstudio.localhost.localstack.cloud:4566 on your browser to view your events.

Introducing LocalStack SDK for Python

We’re excited to announce the preview release of our official LocalStack SDKs for Python. LocalStack offers internal developer endpoints for interacting with emulated services such as SNS, SQS, SES, and DynamoDB, as well as proprietary features like the Chaos API and Cloud Pods. Previously, these endpoints, which are located at /_localstack and /_aws paths and are not part of the official AWS API, required tools like cURL or HTTP REST clients for access.

The new LocalStack SDKs provide a programmatic way to access these REST APIs, offering an object-oriented interface for simpler interaction. Key features of the SDKs include:

• Saving, listing, loading, and deleting Cloud Pods.
• Managing fault configurations for the Chaos API.
• Automatically resetting service states.
• Listing SQS queue messages without side effects.
• Retrieving and deleting sent SES messages.
• Managing SNS platform messages, SMS, and subscription tokens.

These SDKs are ideal for use in your integration test suite, allowing you to reliably test locally deployed infrastructure and utilize our proprietary features like Cloud Pods to bootstrap your testing environment or the Chaos API to simulate unexpected outages at the infrastructure level.

For usage examples and more information, visit our LocalStack SDK for Python documentation.

New default EventBridge provider

The new native EventBridge provider, introduced in version 3.5.0, is now the default EventBridge provider in LocalStack 4.0. This provider enables the creation of complex event patterns, routing events to multiple targets, and creating archives and replaying events, allowing you to simulate real-world event workflows. It offers a robust emulation environment for creating and managing custom EventBridge buses, rules, event patterns, targets, and more. Additionally, the provider fully supports LocalStack features such as Cloud Pods and multi-account/multi-region event transmission on your local machine.

The new EventBridge provider now includes a native Python event rule engine, which provides improved performance and eliminates runtime dependencies, though it does sacrifice some AWS parity. To enhance parity, it is advisable to set the EVENT_RULE_ENGINE configuration variable to java. This setting utilizes the open-source library AWS EventRuler, which offers significantly better AWS parity but with slower pattern matching.

These latest enhancements mark a significant step forward in our commitment to delivering a more robust and fine-tuned EventBridge provider. The old EventBridge provider is temporarily available in LocalStack using PROVIDER_OVERRIDE_EVENTS=v1 but we highly recommend migrating as soon as possible since we will drop support for this in the next major release. Check out our EventBridge documentation to learn more!

New default API Gateway provider

The new native API Gateway provider, introduced in version 3.8.0, is now the default API Gateway provider in LocalStack 4.0. The new API Gateway provider has been completely revamped to align REST and HTTP API behavior more closely with AWS. Key updates include support for request and response data mappings, enhanced VTL template rendering for Mapping Templates, improved AWS_PROXY Lambda integration, REQUEST Lambda Authorizer, seamless stage deployments, and support for most AWS integrations.

The old API Gateway provider is temporarily available in LocalStack 4.0 using PROVIDER_OVERRIDE_APIGATEWAY=legacy but we highly recommend migrating as soon as possible since we will drop support for this in the next major release! Check out our documentation for the full feature set.

Unified LocalStack on Kubernetes support

LocalStack now supports running a broader range of AWS services on Kubernetes, expanding beyond the previous support for Lambda functions, ECS Tasks, and EC2 instances. You can now run services like:

• DocumentDB
• MWAA
• RDS (MySQL & MSSQL)

To enable Kubernetes as the runtime backend, set the new CONTAINER_RUNTIME configuration variable to kubernetes. Learn more in our documentation.

New Config Hot Reloading for Lambda Debug Mode

We introduced Lambda Debug Mode in version 3.7.0, designed to improve the debugging experience for Lambda functions. Users set up debugging sessions by specifying a configuration file path with the LAMBDA_DEBUG_MODE_CONFIG_PATH configuration variable. Initially, this configuration was loaded at startup and couldn’t be altered until LocalStack was restarted, which was inconvenient for post-startup changes.

To address this, we’ve implemented hot reloading for the Lambda Debug Mode configuration file. Now, when modifications are detected in the file, the configuration is automatically updated. After debugging a Lambda function, its associated container will automatically stop. This is crucial because reconfiguring an active container is challenging, such as adjusting port configurations. This new functionality also allows for debugging the same Lambda function multiple times, enhancing flexibility in development workflows.

Check out our Lambda Debug Mode documentation to learn more!

Improved UX for IAM Policy Stream

We have introduced several user experience (UX) improvements to the IAM Policy Stream feature on the LocalStack Web Application. This feature simplifies permission management by generating a continuous flow of IAM policies based on the AWS API calls your application infrastructure makes. Here are the key updates we implemented to enhance the user experience:

• Users can now enable the IAM Policy Stream directly from the user interface for better control over permission monitoring.
• A new toggle allows users to switch between a permissive “Soft Mode” for policy warnings and a “Strict Enforcement” mode to identify permission violations.
• Operations and policies are now visually separated for inspecting individual API calls and their permissions, with the ability to hide internal calls.
• The dashboard has been updated to dynamically generate and categorize policies for each API call to allow developers to see the required permissions.
• The dashboard now supports quick resets of the policy stream, permitting users to start anew or reevaluate permission needs from a clean slate.
• Users can view detailed identity-based and resource-based policies, including the specific request parameters involved.

Check out the IAM Policy Stream on our Web Application.

Introducing Stack Overview

As part of our initiative to enhance your understanding and visualization of your locally running cloud app architecture, we have introduced a new Stack Overview feature. You can access this page by navigating to the LocalStack Web Application. This dynamic interface reflects the current state of the LocalStack environment.

The Stack Overview features:

• A summary of deployed resources across various regions and accounts.
• A categorized display of services along with their configurations.
• Quick access to details of resources, including identifiers and endpoints.

To view similar information within a Cloud Pod, ensure your LocalStack container is running and save the Cloud Pod with the ENABLE_POD_RESOURCES=1 configuration enabled. Cloud Pods saved without this setting will not display these details.

Check out the Stack Overview on our Web Application.

New EventBridge Pipes Resource Browser

We’ve launched a new EventBridge Pipes Resource Browser, enabling you to set up direct integrations between event producers and consumers directly from your web browser or the LocalStack Desktop application. EventBridge Pipes was introduced in 3.1, and we’ve now expanded support to include various sources like DynamoDB, Kinesis, and SQS, and targets such as Lambda and Step Functions, along with log destinations and enrichments.

The addition of the EventBridge Pipes Resource Browser completes the development cycle, putting forward our commitment to providing developers with a visual experience for managing local cloud resources effectively.

The features include:

• Creating new EventBridge pipes with configurations like name, description, desired state, source service, and source ARN.
• Configurable options for each pipe, such as source and target parameters, batch size, maximum batching window, and event filtering criteria.
• Enabling logging to track activities and troubleshoot pipe issues.
• Supporting Role ARN for authorizing data transfers and adding tags to organize and categorize pipes.

Check out our documentation to get started with EventBridge Pipes and the Resource Browser.

New Cloud Pods Save/Load Features on Web App

Cloud Pods are persistent snapshots of your application state that can be stored, versioned, shared, and loaded into your instances. We’ve added new capabilities to the LocalStack Web Application that enhance how you create & manage these snapshots:

• Choose from various merge strategies when loading Cloud Pod states (account-region-merge, service-merge, overwrite). These strategies, introduced in version 3.7.0, can now be selected directly from the Web App.
• Select specific services to save when creating a Cloud Pod. For instance, if only DynamoDB and S3 are selected, the Cloud Pod will save the states of these services exclusively, offering more precise control over your state management.

To learn more about how it works, check out the documentation on merge strategy and how you can selectively save your state on our Web Application.

New Ephemeral Instances CLI

We launched the public preview of LocalStack Ephemeral Instances in version 3.6.0 to allow users to run a LocalStack instance in the cloud. This feature is ideal for creating application previews, fostering collaboration, and executing user acceptance testing (UAT) without relying on staging environments. To improve the usability of Ephemeral Instances, we’ve now integrated the experience into the localstack CLI, enabling instance creation & management directly from your terminal.

To get started, use this command:

localstack ephemeral create --name my-demo-instance

The command outputs an endpoint_url which you can use in AWS integrations (like CDK, AWS CLI, or Terraform) to send API requests to the instance. The supported features include:

1. Creating an Ephemeral Instance with options to install LocalStack Extensions and load Cloud Pods.
2. Retrieving logs for an Ephemeral Instance by specifying the instance name.
3. Listing currently running Ephemeral Instances.
4. Deleting Ephemeral Instances by specifying the instance name.

You can learn more about the Ephemeral Instances CLI on our documentation and our handy tutorial to get started with some of our suggested use-cases.

Miscellaneous

• Introducing the new CI Auth Token, replacing the older LocalStack CI Keys to enhance security by isolating individual access from CI pipeline access. Learn more in our blog.
• Python 3.13 Lambda runtime is now supported in LocalStack.
• CloudFormation Custom Resources now support UPDATE and DELETE operations.
• KMS now supports deriving shared secrets using key agreement algorithm.
• Lambda Event Source Mapping now handles empty invocations from a custom Lambda bootstrap.
• Lambda now supports tagging of Event Source Mappings.
• Users can now create a Cloud Pod at the shutdown of an Ephemeral Instance, allowing you to resume your application at the state where you left it off.
• LocalStack Enterprise users can now automatically assign licenses to new workspace members through Single Sign-On.
• LocalStack’s DynamoDB emulation has been upgraded to use the new DynamoDB Local 2.0, which includes support for table deletion protection and the ReturnValuesOnConditionCheckFailure parameter. Additionally, it features configurable maximum throughput for on-demand tables, along with support for BatchExecuteStatement, and ExecuteTransactionRequest API.
• Several new features have been introduced in the LocalStack Resource Browsers:
  • Edit and view policies directly within the IAM Resource Browser.
  • View the value of your API keys in the API Gateway Resource Browser.
  • Enable continuous updates and testing without redeployment through Lambda Hot Reloading in the Lambda Resource Browser.

Learn more

To learn more about the new functionalities and features of LocalStack 4.0, you can:

• View our release notes on GitHub.
• Navigate to our Developer Hub and try out sample applications to get started.
• Attend our LocalStack Community Event to know more about the 4.0 release.

To get started with using LocalStack 4.0 features:

• Migrate to LocalStack 4.0 by following our migration guide.
• Check out our documentation on these features & services for a lightning-fast development loop.
• Connect with us on LocalStack Slack Community for feedback, bug reports, or suggestions.

Conclusion

Our long-term vision is to build the leading cloud development platform and tools for local cloud development while shaping the industry to prioritize developer experience (DevX) in all cloud and managed service offerings. Our vision extends beyond individual cloud emulators to building a unified multi-cloud developer tooling ecosystem, and we have made significant progress in this with our new Snowflake emulator (and more on the way!). Our next steps will be to expand our offerings to include advanced development tools, hybrid cloud support, enhanced test data management, pre-seeding capabilities, and a multi-cloud tooling ecosystem while addressing the full range of challenges cloud developers face.

Alongside ongoing advancement in our platform, here’s what to expect in the coming months:

• Expanding SDK support for popular testing frameworks like JUnit and PyTest, with additional tools planned for future releases.
• Streamlining transitions between LocalStack and AWS by reducing the need for custom configurations and manual adjustments.
• Providing developers with robust tools to debug, analyze, and iterate on cloud applications, including event debugging and simplified IAM policy management.
• Addressing enterprise requirements by optimizing LocalStack for corporate environments and Kubernetes clusters to help reduce cloud expenses.
• Enhancing visibility into Infrastructure stacks, DevOps workflows, and CI pipelines with interactive tools and detailed analytics for seamless observability.
• Improving Resource Browsers with rich visual insights and detailed inspection capabilities, enabling in-depth debugging and analysis from the web interface.

We’re deeply grateful to our community for shaping LocalStack into a robust platform for local cloud development. Our mission remains the same — give developers efficient, local-first, high-fidelity cloud environments, freeing them to focus on building great products. Your support & feedback drives us forward as we make LocalStack even more adaptable to your needs. Keep an eye on our future announcements & product updates!