Open Serverless (osls) review
A YAML-based framework for packaging and locally running AWS Lambda services.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
Open Serverless (osls) is an open-source command-line framework for defining and deploying AWS serverless applications. Teams describe a service in serverless.yml, including Lambda functions, event sources, IAM permissions and supporting CloudFormation resources. It is aimed at developers maintaining AWS-based serverless applications who want configuration, packaging and local execution in one CLI. The project is a maintained continuation of Serverless Framework v3, and its stated focus is continuity for existing applications rather than adding major new feature areas.
The workflow covers more than function definitions: osls can generate CloudFormation resources, package infrastructure into a deployment-ready directory, and run functions locally. Configuration also includes Lambda layers, function URLs and runtime settings, while plugins can extend commands and configuration. Its documented ecosystem centers on AWS Lambda, AWS CloudFormation and Amazon S3; deployment is AWS-focused rather than multi-cloud. The CLI is distributed as an npm package and provides the osls, sls and serverless commands, which may suit teams already working with those command names and YAML-based service configuration.
The framework itself is free and open source, but that does not make deployments cost-free: AWS infrastructure and usage may incur separate charges. The supplied support channels are community and documentation, so teams should be comfortable relying on those resources. Choose osls when AWS Lambda is the target and local execution plus packaging are useful parts of the development workflow. Consider an alternative if multi-cloud deployment or a roadmap centered on major new feature areas is important; this project’s scope and stated direction are focused on maintaining AWS applications.
Open Serverless (osls) pros and cons
- Where it wins
- Defines Lambda functions, event sources and IAM permissions in YAML
- Packages infrastructure and generates CloudFormation resources
- Supports local execution, plugins, layers and function URLs
- Where it doesn't
- Deployment targets are limited to AWS
- The project prioritizes maintenance over major new feature areas
- AWS infrastructure and usage may incur separate charges
Open Serverless (osls) fact sheet, pricing and score →
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