Public APIs – do you publish these on a separate instance?

Implementing Public APIs for SaaS Applications: Best Practices for API Deployment and Management

In the evolving landscape of software-as-a-service (SaaS) development, providing public APIs has become a key strategy to foster third-party integrations, extend functionality, and enhance the overall ecosystem. When designing such APIs, a common architectural question arises: should the public API be hosted on a separate instance from your internal API, or should they share the same infrastructure?

This article explores best practices for deploying public APIs within SaaS environments, highlighting the benefits and considerations of separating public endpoints from internal systems.

The Rationale Behind Separating Public and Internal APIs

Many SaaS providers choose to decouple their internal and external APIs for several compelling reasons:

Security and Access Control: Isolating public APIs reduces the attack surface, allowing more granular security policies, rate limiting, and monitoring tailored specifically for third-party usage.
Scalability and Performance: Separate instances enable scaling strategies optimized for different workloads. Public APIs often experience unpredictable traffic surges, necessitating dedicated resources.
Development and Deployment Independence: Independent deployment processes allow updates, bug fixes, or changes to be made to public APIs without risking disruption to core internal systems.
Versioning and Compatibility: Maintaining separate endpoints simplifies version management, ensuring stable interfaces for third-party developers.

Architectural Approaches to API Deployment

When establishing a public API, consider the following common deployment patterns:

Dedicated API Endpoint (e.g., api.example.com): Hosting the public API on a subdomain separate from your main application (for instance, app.example.com) offers logical separation. This approach provides clear boundaries and simplifies access management.
Separate Infrastructure (Separate Servers or Cloud Resources): For high-security or high-traffic scenarios, deploying the public API on dedicated servers or cloud instances can further encapsulate and streamline operations.
Shared Infrastructure with Routing Logic: In some cases, a unified infrastructure with routing layers (such as an API gateway) can differentiate between internal and external traffic, applying different policies accordingly.

Practical Considerations

While creating a separate API instance for public access offers many advantages, it also introduces complexity:

Development Overhead: Maintaining multiple codebases or deployment pipelines may increase operational burden.
Synchronization and Consistency: Ensuring that public and internal APIs remain consistent in core functionality demands disciplined versioning and documentation.
Security Configuration: Separate instances require dedicated security configurations, including access tokens,