OPA vs. Google Zanzibar: A Brief Comparison

OPA vs. Google Zanzibar: A Brief Comparison

Two of the most popular policy engines for building granular authorization systems at scale. Selecting the right solution for your needs is not a simple task, and this post will assist you in making the right decision.



Authorization is a crucial aspect of any modern software system, governing who can access what resources. As systems grow in complexity and scale, managing authorization becomes increasingly challenging.

In this post we will explores two powerful solutions for addressing this issue: the Open Policy Agent (OPA) and Google’s Zanzibar.

But before delving into the details of each of them, let's understand the problem space they're solving.

The Challenge of Authorization at Scale

Yet it starts simple, managing authorization becomes increasingly complex as applications accumulate a multitude of resources.

Traditional access control mechanisms, such as RBAC and ACLs, fall short in this context due to their inability to handle the growing complexity and granularity of authorization requirements.

As an example, assigning different access levels to various resources for employees within a large enterprise using these traditional methods results in a convoluted and hard-to-maintain system.

Beyond that, scalability challenges arise when dealing with a large volume of data. Traditional ACLs, which necessitate separate access rules for each resource, are not suited for modern data architectures.

Managing access in this manner not only hampers scalability but also introduces inefficiencies and complexities in data management.

Solutions or we might say systems like Opa and Google’s Zanzibar aim to address the limitations of traditional mechanisms as products and applications continue to evolve.

Open Policy Agent

Open Policy Agent (Opa) is an open-source, general-purpose policy engine that leverages Rego - a declarative language that simplifies the process of defining authorization rules as a code.

This flexibility is invaluable, as it empowers Opa to adapt to various access control models, such as Role-Based Access Control (RBAC), Attribute-Based Access Control (ABAC), and even Relationship-Based Access Control (ReBAC) with necessary customizations.

Opa is a powerful ally for organizations that require granular and dynamic access control across their systems.

Its decentralized policy management ensures that different teams can independently define and maintain their policies, providing a streamlined and agile approach to access control.


Opa's strengths lie in its:

Policy-as-Code: Utilizing code to define policy has its own advantages such as; ensuring auditable access control policies while offering flexibility and automation for efficient and secure authorization management.

Portability: Opa supports multiple data formats and query languages, making it adaptable to various applications and use cases. Also it has a Robust ecosystem with plugins and multiple engines

Decentralized Policy Management: It allows teams to define and manage policies independently, promoting decentralized control over access.

Contextual Awareness: With Opa you can define policies that make authorization decisions with considering the contextual information, such examples are user's location, device, or time of access.


Complex Configuration: Setting up and configuring Opa policies can be intricate, especially for newcomers.

Scalability Challenges: While Opa can handle complex policies, it might face scalability limitations in high-demand environments.

Google Zanzibar

Google Zanzibar, on the other hand, is a scalable, globally distributed system for managing access control.

Google developed it to address their complex authorization needs for various services and products including; YouTube, Drive, Calendar, Cloud and Maps.

At the heart of Zanzibar lies a graph-based approach to authorization. This innovative design leverages the power of graphs, a data structure composed of interconnected nodes and edges, to efficiently manage and enforce access control policies.

In the context of access control, the graph represents relationships and dependencies between entities, such as users, resources, and permissions.


Zanzibar stands out for:

Scalability: The power of this graph-based approach lies in its ability to efficiently scale with growing complexity. As the number of users, resources, and permissions increases, Zanzibar can seamlessly adapt, maintaining low latency and high performance even in globally distributed environments.

Consistency: Zanzibar offers strong consistency guarantees, ensuring that access control policies are consistently enforced across the system. It has its own data-format(relation tuples) to store authorization data and battle tested methods (such as zookies) to prevent inconsistencies.

ReBAC: Zanzibar excels in managing Relationship-Based Access Control (ReBAC) and relationship hierarchies. It can efficiently handle complex authorization scenarios that involve intricate relationships between users, resources, and permissions.


Complex Implementation: Implementing Zanzibar can be challenging due to its global-scale architecture, which might be overkill for smaller applications.

Lack of ABAC: Zanzibar don't support attribute based access control (ABAC) and contextual authorization queries by default.

How to Decide

Choosing between Opa and Zanzibar depends on your specific requirements and context. Here are some factors to consider when making this decision:

  1. Scale: If your application or services tend to get big with increasing resources, Zanzibar's architecture may be more suitable. I’m referring a organizational scale on this.

  2. Complexity: If you require fine-grained, intricate policies with attributes and dynamic data, Opa's flexibility might be advantageous. However, if your policies are mostly relationship based such as nested hierarhies, groups, etc Zanzibar is the right choice.

  3. Community and Support: Opa benefits from a robust open-source community, offering extensive support and resources. In contrast, Zanzibar has a emerging community and there are couple solutions out there that you can implement Zanzibar. We are one of them; Permify, an open source authorization service that is based on Zanzibar, we’re trying to make Zanzibar available to everyone and help them to build robust authorization systems.

  4. Compliance and Auditability: If you operate in highly regulated environments, or auditability is a top priority, Zanzibar's structured data format (relational tuples) provides strong consistency and it's much easier to track, monitor and detect data activity.

  5. Existing Infrastructure: Consider your existing technology stack and how well each solution can be integrated. Opa's versatility may make it a better fit for a diverse ecosystem, while Zanzibar may be more challenging to implement.


Authorization is a critical aspect of modern software systems, and managing it at scale can be a daunting task.

Opa and Google Zanzibar are two powerful solutions, each with its own strengths and weaknesses.

Your choice between the two should depend on the specific needs of your application, considering factors like scale, complexity, support, compliance, and existing infrastructure.

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