Open Policy Agent (OPA) Overview

Overview

The Open Policy Agent (OPA) is a general-purpose policy engine backed by the Cloud Native Computing Foundation (CNCF). It is used for policy-based control and governance across various software systems in the cloud-native environment. OPA is a framework that helps translate written security policies into executable code for every stack layer.

OPA provides a high-level declarative language known as Rego, which allows policy decision-making to be offloaded from your software, decoupling policy enforcement from decision-making. This way, you can consolidate policy enforcement across a wide variety of software and make changes to policy without needing to modify the software itself.

OPA can be used for various policy decisions, including authorization and admission control in microservices or Kubernetes, data filtering and manipulation in data services, and more.

Its use in CNCF primarily focuses on Kubernetes and other cloud-native systems, where it can provide robust, flexible policy controls. For instance, OPA can work as an Admission Controller in a Kubernetes cluster to enforce policies on the Kubernetes API server.

Keep in mind that OPA can be integrated into any service. It exposes a set of APIs that allow the services to offload policy decisions to OPA and can be deployed as a sidecar, host-level daemon, or library, depending on the use case.

Open Policy Agent Policies

A Policy is a set of organizational rules, permissions for app authorization, Kubernetes admissions control, infrastructure, builds and deployment, data filtering, and much more.

Treating Policy as code provides all the benefits of treading anything as code — collaboration, peer review, testing, static analysis, linters, and much more. No more PDF documents!

Decoupling Policy from application and business logic means the Policy can change independently of the application life cycle. The Policy may be shared across teams and functions. Clear separation of responsibilities is a significant advantage.

Open Policy Agent Components

OPA, which stands for Open Policy Agent, is an open-source policy engine that enables policy-based control over applications and services. It is designed to provide a unified approach to policy enforcement across various technology stack layers. OPA evaluates policies against incoming requests and makes decisions based on those policies.

The main components of Open Policy Agent (OPA) are as follows:

1. Rego: Rego is the policy language used by OPA. It is a declarative language specifically designed to write policies. Rego allows you to express complex rules and logic to define policies that govern access control, data filtering, and other policy enforcement aspects.

2. REST API: OPA exposes a RESTful HTTP API that allows clients to interact with it. This API manages policies, queries policy decisions, and evaluates requests against the defined policies.

3. Decision Engine: The decision engine is the core of OPA, responsible for evaluating policies and making policy decisions based on incoming requests. It uses Rego policies for assessing proposals and produce allow/deny decisions or additional data for the application to act upon.

4. Data Storage: OPA provides a pluggable data storage system where you can store external data used in policy evaluation. This allows you to create dynamic policies that depend on external state and data.

5. Integration Hooks: OPA supports integration with various applications and services through integration hooks. These hooks allow you to incorporate OPA into your existing infrastructure and use it for policy enforcement.

6. Policy Bundles: Policy bundles are collections of policies and data that can be distributed and managed together. They allow you to package up a set of related policies and data into a single unit for easier distribution and versioning.

7. Language Bindings: OPA offers language bindings for multiple programming languages like Go, Java, Python, JavaScript, etc. These bindings enable developers to integrate OPA directly into their applications, making enforcing policies at various application stack layers easier.

Open Policy Agent Components

Deployment of Open Policy Agent

Depending on your specific use case and requirements, several options are available for deploying OPA. Here are some standard deployment options:

1. OPA Standalone Deployment: You can deploy OPA as a standalone service on a server or in a containerized environment. This allows you to have a centralized OPA instance that evaluates policies and enforces them across different applications and services.

2. Kubernetes Admission Controller: OPA can be deployed as a Kubernetes Admission Controller. Integrating OPA with Kubernetes allows you to enforce custom admission policies for Kubernetes resources before they are created or modified.

3. Gatekeeper: Gatekeeper is a Kubernetes admission controller that uses OPA under the hood. It allows you to enforce policies through Kubernetes Custom Resource Definitions (CRDs) and the Rego language, which OPA uses. Gatekeeper provides a higher-level, more user-friendly way to define and manage policies in Kubernetes.

4. Envoy External Authorization: If you are using the Envoy Proxy as part of your service mesh architecture, OPA can be deployed as an External Authorization Server for Envoy. It allows you to make authorization decisions based on policies defined in OPA before allowing or denying requests for your services.

5. Istio Mixer Adapter: Istio is another popular service mesh solution, and OPA can be integrated as a Mixer adapter to enforce policy-based access control for service communication.

6. Embedded in Applications: Sometimes, you may embed OPA directly into your applications. This allows your applications to offload authorization decisions to OPA without relying on a separate service or proxy.

7. Custom Integration: OPA is highly flexible and can be integrated into various environments through custom integrations, depending on your specific use case.

Conclusion

In summary, you should use Open Policy Agent (OPA) because:

1. Flexibility: OPA offers a general-purpose policy engine suitable for various systems, from microservices to cloud-native infrastructures.
2. Decoupling: It allows you to separate policy decision-making from enforcement, enabling centralized policy management without altering software.
3. Unified Policy Language: With its high-level declarative language, Rego, you can express intricate rules and logic for policies.
4. Cloud-Native: Backed by the Cloud Native Computing Foundation (CNCF), it’s optimized for cloud-native environments.
5. Dynamic Policy Management: Treating policies as code promotes collaboration, testing, and static analysis, eliminating traditional documentation hassles.
6. Integration: OPA can be seamlessly incorporated into various systems, be it Kubernetes, Envoy, or custom applications, via its robust API and language bindings.
7. Safety: Enables clearer separation of responsibilities, enhancing security and organizational clarity.

In essence, OPA provides a powerful, flexible, and cloud-optimized policy management tool that streamlines and secures policy enforcement across different systems.