Open Policy Agent

Overview

Open Policy Agent (OPA) is an open-source engine for expressing and evaluating rules across software systems. It suits teams that need the same policy logic to serve infrastructure and applications; its breadth is useful, but puts integration and security configuration in the team’s hands.

Policies use Rego, a declarative language for rules over hierarchical data. OPA can evaluate structured input and return structured output, so teams can model decisions for different systems without tying policy logic to one enforcement point. It is a graduated Cloud Native Computing Foundation project.

Its integrations include Kubernetes, Terraform, Envoy, and code editors. For related tools, browse Infrastructure Policy as Code Tools.

Key features

Multiple evaluation paths

Teams can evaluate policies through a REST API, Go API, WebAssembly, or custom evaluators using OPA’s intermediate representation. That range accommodates a remote policy service as well as embedded evaluation, but OPA makes the decision rather than enforcing it: the integrating application or platform must act on the result.

OPA’s use cases span microservices, Kubernetes, CI/CD pipelines, and API gateways. It supports policy testing, runtime enforcement, CI/CD integration, admission control, and policy reporting. For Kubernetes admission control, its documentation recommends OPA Gatekeeper, rather than treating the general-purpose engine alone as the complete admission-control setup.

Policy distribution and operations

OPA bundles distribute policy and data to instances; discovery bundles distribute flexible configuration. Management interfaces support policy distribution, status and health checks, and decision-log collection. These capabilities help teams operate policy across instances, though they still need to design how policies are authored, distributed, and acted upon in their systems.

Infrastructure formats

Supported infrastructure-as-code inputs include Terraform plan JSON, JSON, and YAML. This gives teams several common structured formats to evaluate, while Rego remains the policy language.

Pricing

Open Policy Agent is free and open source. The Open Policy Agent plan costs nothing and is licensed under Apache License, Version 2.0. There are no paid tiers or seat and usage quotas in the plan described, making it suitable for teams that can operate the software themselves without a subscription.

Free does not mean configured security: authentication and authorization are off by default. Teams securing OPA’s API should configure TLS, authentication, and Rego-based authorization. The installation guide supports macOS, Linux/Unix, Windows, and Docker, and provides binary checksums by appending .sha256 to a binary filename.

Platforms

OPA is listed for API, Linux, macOS, self-hosted, web, and Windows environments. Installation options include macOS, Linux/Unix, Windows, and Docker. Its evaluation interfaces provide additional ways to integrate policy into software, including Go and WebAssembly runtimes.

Who it's for

OPA is a strong fit for engineering and platform teams that need a reusable policy layer across services, infrastructure, and delivery pipelines, especially when they can maintain Rego policies and configure their own deployment. Kubernetes teams can use it with Gatekeeper for admission control. Teams looking for a narrow, turnkey control rather than a general-purpose engine may prefer a more focused tool.

Users can talk with other users and maintainers through the OPA Slack community. The project also lists third-party companies offering commercial support; those listings are not vetted endorsements. Security issues should be reported to the OPA security team by email.

Pros and cons

Pros

• Broad evaluation choices: REST, Go, WebAssembly, and custom evaluators let teams choose how policy decisions reach their software.
• Reusable policy across systems: Its general-purpose design and integrations cover use cases from microservices to infrastructure and CI/CD.
• Free, permissively licensed software: The free Apache-licensed plan avoids subscription costs.
• Operational interfaces: Bundles, health and status checks, and decision logs support managing policies across OPA instances.

Cons

• Security needs deliberate setup: Authentication and authorization are off by default, so teams must configure protections before securing the API.
• Integration remains the user’s responsibility: OPA separates decisions from enforcement, leaving each system to apply the result.
• Kubernetes admission control has a recommended companion: The documentation points to Gatekeeper, adding a distinct component to that use case.

Alternatives

Terraform is a better fit for readers seeking infrastructure provisioning with policy features alongside a free plan capped at 500 managed resources, one concurrent remote run, and one concurrent agent run.

Conftest is a free Apache-licensed option for readers seeking a more focused policy-testing tool on Linux, macOS, or Windows.

Fairwinds Polaris is a free open-source policy engine aimed at small teams.

Google Cloud Terraform Policy Validation is a free beta client-side tool for Terraform policy validation.

AWS CloudFormation is a free CloudFormation service, with underlying AWS resources billed at their own rates.

cfn-lint is a free MIT-0 licensed choice for readers working with CloudFormation templates.

Cloud Custodian is a free Apache 2.0 open-source alternative.

KICS is a free open-source alternative for infrastructure policy as code.

Verdict

Choose OPA if your team needs policy decisions shared across several software and infrastructure systems and can own the Rego, integration, and security configuration. Its flexible evaluation interfaces and zero-cost Apache license are compelling; look elsewhere if you want a narrowly scoped tool that requires less integration or operational responsibility.