From Silos to Shared Libraries: A Practical Guide to Inner Source Adoption

In our previous posts, we explored inner source principles and building developer communities. Now, let’s get practical. How do you actually transition from siloed team-specific code to shared libraries? Let’s explore a detailed roadmap for success, based on patterns I’ve seen out in the wild.

The Journey from Silos to Sharing

The transition to shared libraries isn’t just a technical change - it’s an organizational transformation. Most organizations discover this the hard way, focusing initially on the technical aspects while underestimating the importance of cultural change and clear processes. Let’s explore how to address both aspects effectively.

Finding Your First Wins

A common pattern emerges in most organizations beginning their inner source journey: duplicate implementations of core functionality across teams. Authentication, logging, data validation - these fundamental needs often spawn multiple implementations, each slightly different, each maintained separately.

Here’s what this often looks like in practice:

graph TD
    subgraph "Before Shared Libraries"
        A[Team A] --> AA[Auth Impl A]
        B[Team B] --> BB[Auth Impl B]
        C[Team C] --> CC[Auth Impl C]
        D[Team D] --> DD[Auth Impl D]
    end

The most successful transitions often start with these common utilities. They’re the perfect candidates because they solve universal problems, have clear boundaries, and offer immediate value through standardization. JWT token validation is a classic example - it’s a critical security component that many teams implement independently, despite the core requirements being identical across the organization.

The Art of Governance

The question of ownership and maintenance is often the first major hurdle in library sharing initiatives. Different governance models have emerged, each with their own strengths and challenges.

Centralized Model (Common Pitfalls)

graph TD
    subgraph "Centralized Model"
        PT[Platform Team]
        PT --> L1[Library 1]
        PT --> L2[Library 2]
        PT --> L3[Library 3]
        T1[Team 1] -.->|Requests| PT
        T2[Team 2] -.->|Requests| PT
        T3[Team 3] -.->|Requests| PT
        T4[Team 4] -.->|Requests| PT
    end

The centralized approach, where one team owns all shared libraries, often appears attractive initially. However, this model frequently becomes a bottleneck as the number of libraries and consuming teams grows. The maintaining team becomes overwhelmed with pull requests and feature requests from teams they’ve never worked with.

Federated Model with Guardrails (Recommended)

graph TD
    subgraph "Federated Model"
        PTE[Platform Team]
        PTE -->|Standards & Tools| AT[Auth Team]
        PTE -->|Standards & Tools| DT[Data Team]
        PTE -->|Standards & Tools| IT[Infra Team]
        
        AT -->|Owns| AL[Auth Libraries]
        DT -->|Owns| DL[Data Libraries]
        IT -->|Owns| IL[Infra Libraries]
        
        T1[Team 1] -->|Contributes| AL
        T2[Team 2] -->|Contributes| DL
        T3[Team 3] -->|Contributes| IL
    end

A more sustainable approach is the “federated model with guardrails.” In this model, teams maintain libraries within their domain of expertise, while a platform team provides tools, standards, and support infrastructure. This approach leverages existing domain knowledge while ensuring consistency.

Security: The Foundation of Shared Code

Security becomes particularly critical when code is shared across an organization. A vulnerability in a shared library can affect multiple systems simultaneously. This reality has led to the development of robust security-first approaches to library development.

flowchart TD
    subgraph "Security Review Process"
        A[New Library Proposal] --> B{Security Review}
        B -->|Pass| C[Implementation]
        B -->|Fail| D[Security Improvements]
        D --> B
        C --> E{Vulnerability Scan}
        E -->|Pass| F[Release]
        E -->|Fail| G[Fix Vulnerabilities]
        G --> E
    end

Case Study: Authentication Library Consolidation

A common pattern in growing organizations is the proliferation of authentication implementations. One notable success story comes from a large company, where multiple teams had developed their own authentication solutions over time.

graph TD
    subgraph "Before"
        T1[Team 1] --> A1[Auth 1]
        T2[Team 2] --> A2[Auth 2]
        T3[Team 3] --> A3[Auth 3]
    end
    
    subgraph "After"
        T4[Team 1] --> SA[Shared Auth]
        T5[Team 2] --> SA
        T6[Team 3] --> SA
        SA -->|Managed by| AT[Auth Team]
        AT -->|Support from| PT[Platform Team]
    end

The consolidation approach involved:

1. Creating a wrapper library that could support multiple underlying implementations
2. Implementing comprehensive monitoring and logging
3. Allowing gradual migration at each team’s pace
4. Providing clear metrics on performance and reliability

The results demonstrated the value of this approach:

• Consolidated authentication into a single, well-tested library
• Reduced security incidents by 80%
• Improved development velocity for new services
• Increased compliance team confidence

The Path Forward

Transitioning to shared libraries requires careful balance. The goal isn’t to create perfect, universal solutions, but rather to develop maintainable, secure, and useful code that improves developer productivity and system reliability.

graph LR
    A[Identify Common Code] --> B[Establish Governance]
    B --> C[Set Security Standards]
    C --> D[Create Migration Plan]
    D --> E[Measure Success]
    E --> F[Expand Adoption]

Key factors for success include:

• Starting with well-defined, commonly needed functionality
• Establishing clear governance and maintenance processes
• Implementing robust security practices
• Developing comprehensive testing strategies
• Allowing for gradual adoption

Remember: The most successful shared libraries aren’t just well-written code - they’re well-documented, well-tested, and supported by clear processes that make them truly valuable to the organization.