Streamlining Shared Libraries and OpenAPI Specs: Publish Once, Reuse Everywhere

In the world of microservices, reusability is more than just a nice-to-have — it’s a necessity. Yet, across many organizations and projects, I’ve noticed a recurring pain point: handling shared libraries and OpenAPI specifications efficiently.

Whether you’re a developer or DevOps engineer, chances are you’ve struggled with:

• Keeping OpenAPI specs in sync across services
• Copy-pasting utility code or DTOs between repositories
• Conflicting library versions in downstream services
• Manual updates across multiple microservices for every change

This isn’t just frustrating — it’s fragile and unsustainable.

The Problem: A Mess of Redundancy and Inconsistency

Let’s take a common scenario. You’ve got multiple microservices that share:

• DTOs (Data Transfer Objects)
• Client SDKs generated from OpenAPI specs
• Common utility classes (e.g., authentication handlers, logging)

Now imagine a small change to the OpenAPI YAML or a utility method. You’ll often find yourself:

• Making sure every team is aware and updated
• Fixing mismatched versions or broken contracts in CI/CD
• Making the change in one repo
• Copying the updated code to 4–5 other services

Sounds familiar? That’s time-consuming, error-prone, and anti-DevOps.

The Solution: Package Your Shared Libraries & Specs

Here’s a cleaner, scalable, and DevOps-friendly approach:

1. Maintain a Dedicated Repository

Have a GitHub/GitLab repository specifically for:

• Shared DTOs
• Utility libraries
• OpenAPI specs (YAML/JSON)

Structure it well (e.g., src/main/java or /specs folder) and version it properly.

2. Publish as a Package

Depending on your ecosystem, publish the shared components as versioned packages:

package manager for different tech stack

For OpenAPI, you can even publish the generated SDKs as packages (e.g., via Swagger Codegen or OpenAPI Generator).

Example for Java using GitHub Packages:

<dependency>
  <groupId>com.spring</groupId>
  <artifactId>spring-boot-library</artifactId>
  <version>1.0.0</version>
</dependency>

3. Consume in Microservices

Now in any microservice, instead of copying files:

• Just add the dependency
• Let CI/CD pull the right version
• Get consistent, version-controlled functionality

Changes? Just bump the version. Everyone using v1.2.0 keeps their current state. Others may upgrade to v1.3.0 when ready.

visual representation on how to use this shared lib

Versioning and Backward Compatibility

The key to a reliable shared model is semantic versioning and backward compatibility.

Use this pattern:

• MAJOR — Breaking changes (e.g., rename DTO fields)
• MINOR — Additive changes (e.g., new fields/methods)

Tools like OpenAPI Generator and Swagger can even validate whether your new spec breaks existing clients.

Bonus: Secure and Scalable Publishing

• Use access tokens to authenticate and push to GitHub Packages or GitLab Registry
• Automate the package publishing process via GitHub Actions or GitLab CI
• Set up automated version tagging using commit messages or manual triggers

The Benefits

✅ Cleaner CI/CD pipelines — no copy-paste, just dependency management ✅ Faster onboarding — new services just consume shared logic instantly ✅ Improved consistency — same DTO, same validation, same SDK ✅ Easier upgrades — microservices choose when to upgrade ✅ True DevOps — infrastructure and code evolve together

Final Thoughts

The best engineering practices aren’t just about writing scalable services — they’re about building scalable teams and scalable processes.

By packaging and reusing shared libraries and OpenAPI specs, you reduce friction, increase confidence, and empower your team to move fast without breaking things.

Let’s shift from “copy-paste and pray” to “publish and reuse.”

Proof of Concept(PoC)

https://github.com/SanthoshKumar-Ravi/spring-boot-library