OPA vs Zanzibar: Why Open Policy Agent Makes Authorization Refreshingly Simple
When it comes to building authorization systems at scale, developers often find themselves caught between two powerhouse approaches: Open Policy Agent (OPA) and Google's Zanzibar model. While both solve the challenge of "who can do what," they couldn't be more different in their philosophy and implementation complexity.
The Simplicity Factor: Policy-as-Code vs Graph Complexity
Unlike OPA, the Zanzibar paper describes an opinionated authorization model: objects have relationships to subjects, and determining whether a user has a permission means walking this graph to find a path. This fundamental difference highlights why OPA feels so much simpler to work with.
OPA's Approach: Write human-readable policies in Rego, a declarative language that reads almost like English. Need to check if a user can access a document? Write a simple rule that evaluates conditions directly.
Zanzibar's Approach: Model everything as a complex relationship graph where you need to understand object hierarchies, relationship tuples, and graph traversal algorithms just to get started.
OPA tends to require a heavier initial investment than a graph-based authorization model, like Zanzibar, but this "investment" is primarily in learning Rego syntax rather than wrestling with complex graph relationships and infrastructure.
Performance and Deployment: Edge-First vs Centralized
Compared to policy-as-code, graph-based systems exhibit lower performance and are practically unfeasible to run at the edge due to their size. They also come with higher latency, owing to their non-local nature.
This is where OPA truly shines. You can embed OPA directly into your applications, run it at the edge, or deploy it as a lightweight sidecar. Zanzibar-inspired systems require centralized graph databases and complex distributed architectures.
Real-World Adoption: Who's Building on OPA
The OPA ecosystem has exploded with SaaS platforms and tools that make authorization even simpler:
Major OPA-Based Authorization Platforms:
- Styra DAS - Enterprise policy management platform by OPA's creators
- Permit.io - Low-code authorization platform with OPA backend
- Aserto - Developer-first authorization service built on OPA
- Authzed/SpiceDB - Actually Zanzibar-inspired, but worth noting as alternative
- Oso - Application-level authorization framework (with OPA integration)
Companies Successfully Using OPA:
- Netflix - Policy enforcement across microservices
- Pinterest - API authorization and resource access control
- Chef - Infrastructure policy management
- Atlassian - Internal authorization systems
- Goldman Sachs - Financial services compliance policies
- Shopify - E-commerce platform policy enforcement
- T-Mobile - Telecom infrastructure policies
OPA Integration Tools:
- OPA Gatekeeper - Kubernetes admission controller
- Conftest - Policy testing for configuration files
- Spacelift - Infrastructure as Code policy enforcement
- Fugue - Cloud security compliance
The Comparison Matrix
| Aspect | OPA | Zanzibar |
|---|---|---|
| Learning Curve | Moderate (learn Rego) | Steep (graph theory + relationships) |
| Performance | High (local evaluation) | Variable (network-dependent) |
| Deployment | Anywhere (edge, embedded) | Centralized systems |
| Policy Expression | Flexible, code-like | Relationship-constrained |
| Debugging | Clear policy tracing | Complex graph traversal |
| Ecosystem | Rich SaaS offerings | Limited open-source options |
Why OPA Wins on Simplicity
The beauty of OPA lies in its pragmatic approach. Instead of forcing you to think in terms of complex relationship graphs, OPA lets you express authorization logic the way you naturally think about it:
# OPA Policy Example
allow {
user_has_role[input.user]["admin"]
input.resource.type == "sensitive_data"
}
user_has_role[user][role] {
some assignment in data.role_assignments
assignment.user == user
assignment.role == role
}
This reads like pseudocode but executes with enterprise-grade performance and security.
AuthZEN: The Interoperability Game Changer
While debating OPA vs Zanzibar, there's a crucial development that's reshaping the entire authorization landscape: AuthZEN, an OpenID Foundation working group providing standard mechanisms, protocols and formats to communicate authorization related information between components.
AuthZEN represents a paradigm shift toward authorization interoperability. The specification has evolved rapidly from initial draft in June 2024 to supporting boxcarred requests in January 2025 and search endpoints by February 2025. This means you're no longer locked into a single authorization approach.
Why AuthZEN Matters for OPA vs Zanzibar:
- Vendor Neutrality: AuthZEN defines an Authorization API that allows policy enforcement points to evaluate decisions in a standard way, regardless of whether you use OPA, Zanzibar, or other engines
- Ecosystem Integration: API gateways including Layer 7, Kong, and Envoy are participating in interoperability efforts, with adopters like Workday and Salesforce externalizing authorization
- Future-Proofing: Switch authorization engines without rewriting your entire application integration layer
OPA's AuthZEN Advantage:
OPA's flexibility shines in the AuthZEN ecosystem. Aserto, built on OPA, was one of the co-proposers of the PEP-PDP spec and primary authors of the AuthZEN interop scenario demonstrated by 12 implementations in May 2024. This positions OPA as a first-class citizen in the emerging interoperability standard.
The Bottom Line
OPA enables policy enforcement in various contexts, including microservices, Kubernetes, CI/CD pipelines, API gateways, data protection, SSH/Sudo and container exec control, and Terraform risk analysis. With AuthZEN standardizing authorization APIs, OPA's versatility becomes even more valuable – you get simplicity today with guaranteed interoperability tomorrow.
While Zanzibar-style systems excel in specific use cases requiring complex hierarchical relationships (think Google Drive's sharing model), OPA provides a more approachable path to robust authorization for the majority of applications. The thriving ecosystem of OPA-based SaaS platforms means you can often get started with enterprise-grade authorization in hours, not months.
Choose OPA when you want authorization that's powerful enough for enterprise scale but simple enough that your entire team can understand and maintain it.
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