Announcing the LocalStack for AWS 4.12 Release

Introduction

We’re excited to share the release of LocalStack for AWS 4.12. This release introduces support for Lambda Managed Instances, providing AWS cloud users with more predictable costs for their Lambda workloads and access to specialized compute hardware. We’ve also added comprehensive unit testing capabilities for Step Functions, allowing developers to validate individual states and test error handling scenarios without deploying to AWS.

This release includes expanded Glue API support with user-defined functions and column statistics, improvements to the S3 Tables provider with tagging and encryption configuration support, enhanced load balancing capabilities with NLB TCP listener emulation and ALB HTTPS target support, and updates across multiple services, including EventBridge Pipes, IAM, CloudWatch Logs, CloudFormation, ACM, S3, MWAA, EC2, SNS, and S3 Control.

Get your free LocalStack account to access the latest features and enhancements in LocalStack for AWS 4.12!

How to upgrade?

To upgrade to LocalStack for AWS 4.12 using the LocalStack CLI, run:

localstack update all

If using Docker CLI or Docker Compose, update the Docker image:

docker pull localstack/localstack:4.12.0 # Community Edition
docker pull localstack/localstack-pro:4.12.0 # Pro Edition

Pin version 4.12.0 in your Docker configuration to ensure reproducibility.

What’s new in LocalStack for AWS 4.12?

• Support for Lambda Managed Instances
• Enhanced Unit Testing for AWS Step Functions
• New enhancements in the S3 Tables provider
• Expanded Glue API Support
• Miscellaneous

Support for Lambda Managed Instances

AWS Lambda now supports Managed Instances, a new AWS Lambda execution mode that allows for predictable pricing when handling a high volume of Lambda invocations. Functions are deployed to a customer’s EC2 instances, allowing for the use of specialized hardware and explicit control over how many Lambda functions run on each.

LocalStack now supports Lambda Managed Instances, enabling developers to:

• Test persistent Lambda execution environments locally before deploying to AWS.
• Configure instance count, concurrency limits, and scaling policies.
• Validate long-running workload behavior in a local development environment.

Learn more in our blog post.

Enhanced Unit Testing for AWS Step Functions

LocalStack now provides comprehensive support for unit testing AWS Step Functions via enhanced TestState API capabilities. The new capabilities enable developers to validate individual states, test error handling scenarios, and verify state transitions without deploying to AWS.

Key features include:

• Mocking of state outputs and errors without invoking downstream services, enabling true unit testing of state machine logic.
• Mock response validation against AWS API models.
• Testing specific states within a full state machine definition.
• Support for Map state (inline and distributed).
• Advanced state execution configuration, like setting the number of retries and map iteration failure count.

This enables faster iteration cycles and more reliable state machine development by catching issues early in the development process. Learn more in our blog post.

New enhancements in the S3 Tables provider

LocalStack’s S3 Tables provider now includes the following enhancements:

• Added support for the ListTagsForResource API.
• Added support for encryption configuration APIs at both bucket and table levels. Actual encryption enforcement is not yet implemented.

Expanded Glue API Support

LocalStack’s Glue provider now includes the following enhancements:

User-Defined Functions (UDF)

Added support for managing user-defined functions in Glue:

• CreateUserDefinedFunction
• GetUserDefinedFunction
• UpdateUserDefinedFunction
• DeleteUserDefinedFunction
• GetUserDefinedFunctions

UDF data is stored as part of the database entity, ensuring automatic cleanup when databases are deleted.

Column Statistics

Added support for managing column statistics for tables:

• UpdateColumnStatisticsForTable
• GetColumnStatisticsForTable
• DeleteColumnStatisticsForTable

These APIs are commonly used when configuring Glue as a metastore for data processing frameworks.

Miscellaneous

• Upgraded the kinesis-mock version from 0.5.1 to 0.5.2.
• Added support in CloudFormation v2 for List<AWS::EC2::SubnetId> template parameters.
• Added support for additional RSA key lengths and several EC key types in ACM certificates.
• Added support for the EU LocationConstraint in S3 CreateBucket operation.
• Added support for Airflow 3.0.6 in Managed Service for Apache Airflow (MSAA) provider.
• Added support for the GetInstanceUefiData API in the EC2 provider.
• Implemented support for specifying Tags during S3 CreateBucket operation, and added support for the TagCount field in HeadObject responses.
• Added configurable wait-time controls for CloudFormation resource polling (CFN_NO_WAIT_ITERATIONS) and reduced default sleep intervals, meaning that deploy times for large stacks should be reduced.
• Added configuration options to customize the Libvirt network (EC2_LIBVIRT_NETWORK) and storage pool (EC2_LIBVIRT_POOL) used by EC2, instead of assuming the default names.
• Cognito now supports enforcing HTTPS in OAuth and federated login flows by honoring USE_SSL=1, ensuring all generated authentication URLs use https://.
• Added support for ECS Managed EC2 Instances capacity providers, including CRUD operations, improved status responses, and validation during task execution.
• Added support for the following S3 Control tagging operations for S3 buckets:
  • ListTagsForResource
  • TagResource
  • UntagResource
• Added support for the ListLogGroups operation in CloudWatch Logs.
• EventBridge Pipes now supports input transformation for enrichment, including proper handling of JSON arrays and quote stripping for plain text templates.
• Application Load Balancers now support HTTPS targets in target groups, with the load balancer skipping SSL verification for HTTPS targets, matching AWS behavior where self-signed certificates are accepted.
• Improved the IAM SimulatePrincipalPolicy operation to use the IAM Enforcement Engine, providing more accurate policy evaluation decisions. Support for roles and groups as principals has been added.
• Network Load Balancers now support TCP listener emulation, enabling basic NLB functionality for local testing. A new proxy manager handles the creation and lifecycle of TCP proxies for NLB listeners.

Conclusion

LocalStack for AWS 4.12 brings important enhancements to serverless development workflows, with support for Lambda Managed Instances and comprehensive Step Functions testing capabilities. These additions, combined with improvements across tagging, data management, and core AWS services, continue to strengthen LocalStack’s local development experience.

Upgrade to LocalStack for AWS 4.12 today to accelerate your AWS cloud application development with greater confidence and efficiency.