Open Policy Agent

Overview

Open Policy Agent (OPA) is an open-source engine for evaluating policies across software systems. It suits teams that need a shared policy layer across services and infrastructure; its flexibility is valuable, but securing its API takes deliberate configuration.

OPA separates policy decisions from the software that enforces them. Policies use Rego, a declarative language for rules over hierarchical data, and can evaluate structured input to produce structured output. That makes OPA a strong fit when different systems need to apply a common policy approach, rather than when a team needs only a narrowly scoped control.

OPA is a graduated Cloud Native Computing Foundation project, with integrations for Kubernetes, Terraform, Envoy, and code editors. Browse Infrastructure Policy as Code Tools for related options.

Key features

Flexible policy evaluation

Applications can evaluate policies through a REST API, Go API, WebAssembly runtimes, or custom evaluators using OPA's intermediate representation. Teams can choose an integration style that fits their systems, but OPA is an engine to integrate rather than a turnkey enforcement layer: the surrounding software still acts on policy decisions.

Its use cases include microservices, Kubernetes, CI/CD pipelines, and API gateways. OPA supports admission control, runtime enforcement, CI/CD integration, and policy testing. For Kubernetes admission control specifically, its documentation recommends OPA Gatekeeper, a useful distinction for teams planning a Kubernetes deployment.

Policy distribution and operations

OPA bundles distribute policy and data to instances; discovery bundles distribute flexible configuration. Management interfaces support distribution, status and health checks, and decision-log collection. These capabilities help teams operate policies across multiple instances, though they also make OPA a better fit for teams prepared to manage policy distribution and the systems around it.

Supported infrastructure-as-code formats include Terraform plan JSON, JSON, and YAML. The combination of broad input formats and multiple evaluation routes gives teams room to apply policy beyond one infrastructure tool.

Security and support

Authentication and authorization are off by default. Teams exposing the API should configure TLS, authentication, and Rego-based authorization; this is an important deployment responsibility, not a minor setup detail. Suspected security issues can be reported to the OPA security team by email. Users can also turn to the OPA Slack community to talk with other users and maintainers. Commercial support is offered by third-party companies, whose listings are not vetted endorsements.

Pricing

OPA is free and open source under the Apache License, Version 2.0. Its Open Policy Agent plan costs nothing and includes an open-source policy engine. There is no paid tier to weigh against it; the trade-off is that teams must integrate and operate the engine themselves, and any commercial support comes from third parties.

Platforms

OPA supports API, Linux, macOS, self-hosted, web, and Windows environments. Installation guidance covers macOS, Linux/Unix, Windows, and Docker, giving teams common options for local, server, or container deployment. Binary checksums are available by appending .sha256 to a binary filename, a practical verification step when downloading releases.

Who it's for

OPA is best for engineering and platform teams that want to centralize policy decisions across services, infrastructure, and delivery pipelines, and can work with Rego and manage integrations. It is less suitable for teams seeking a managed, ready-configured policy service or a narrow tool that handles one platform-specific task without broader policy integration.

Pros and cons

• Pros: Multiple evaluation options—REST, Go, WebAssembly, and custom evaluators—let teams connect policy to varied software systems.
• Pros: Policy and data bundles, health and status interfaces, and decision logs support coordinated operation across OPA instances.
• Pros: Free, Apache-licensed software avoids a product subscription and supports use across several listed infrastructure and application contexts.
• Cons: Rego and the integration work require engineering effort; OPA does not itself replace the systems that enforce its decisions.
• Cons: API authentication and authorization are disabled by default, so secure deployment requires explicit configuration.

Alternatives

Google Cloud Terraform Policy Validation is a free beta client-side tool for Linux, macOS, and Windows. Choose it when the need is specifically Terraform policy validation rather than a general-purpose engine spanning multiple systems.

Terraform has a free plan at no cost, capped at 500 managed resources, one concurrent remote run, and one concurrent agent run. Choose it when the priority is Terraform infrastructure management within those limits, rather than a general policy engine.

AWS CloudFormation is free for the service itself, while underlying AWS resources are billed at their own rates. It is the alternative to consider for AWS CloudFormation workflows rather than policy enforcement across unrelated systems.

Cloud Custodian is a free, open-source Apache 2.0 option. Conftest is also free and Apache 2.0 licensed. cfn-lint is free, MIT-0 licensed, and supports Python 3.10–3.14. KICS is a free open-source project, and Kyverno is a free open-source project under Apache 2.0. Consider these alternatives alongside OPA when comparing infrastructure policy tools.

Verdict

Choose OPA if your team needs a free, general-purpose policy engine that can connect decisions to multiple software systems and has the engineering capacity to integrate and secure it. Its breadth and flexible evaluation paths are the main reasons to choose it; look elsewhere if you need a managed service or want API security configured by default.