Inner Source @ DB A Story About Open Source Practices at Deutsche Bahn Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Comic: Courtesy Victoria Drake | Source Comic: Courtesy Victoria Drake |  Source 2 

DB Software Development in numbers* Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Lines of Code >450 M Active Git repositories in central GitLab instance >50.000 User in GitLab >10.000 ~22% Inner-source share of Git projects GitLab Groups >13.000 * Last updated: April 2024 3 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Timeline of Inner Source@DB 1999 2002 2006 2011 2016 2021 First inner-source project for the introduction of Java Start of the component library “KOLT” in CVS Management issues order to publish DB Systel internal projects as inner source. Six-week inner source workshop GitLab and Artifactory selected as repositories for inner-source projects Founding of the Inner Source topic team in the architecture guild of DB Systel GmbH 2017 I join 4 

Inner Source — WHY? Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Culture of collaboration Cost reduction Increase Quality Transparency 5 

Inner Source — IMPEDIMENTS Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 6 Separate business enterprises CI infrastructure costs money Inertia and uncertainty 

Inner Source — IMPEDIMENTS Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 7 Separate business enterprises CI infrastructure costs money Inertia and uncertainty 

Problem: Separate business enterprises Solution: Our own software license Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 DB Inner Source License (DBISL) 8 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 9 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Problem: Separate business enterprises Solution: Our own software license DB Inner Source License (DBISL) Use within the DB group free of restrictions Source code is available to everyone Modifications are possible Sharing allowed 4 Freedoms of Open Source 10 The DBISL is Open-Source: github.com/dbsystel 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 11 Contract module: Inner Source Excerpt from the contract toolkit for service systems 4.6 (3) b. The client is in agreement / not in agreement with the internal corporate use of the developed software components under the "DB Inner Source" license by other companies within the group. 

Inner Source — IMPEDIMENTS Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Separate business enterprises CI infrastructure costs money Inertia and uncertainty 12 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Team-maintained Inner Source 13 Team Product Library (Inner Source) owns uses owns 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 14 Community-maintained vs. Team-maintained Inner Source Team Product Library (Inner Source) owns uses Maintainer The maintainers can belong to different teams Library (Inner Source) maintains owns uses 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Community-maintained vs. Team-maintained Inner Source Community-maintained Team-maintained Independence from the product lifecycle Independent of the organizational development of a team Simple integration of collaborators No commitment from an entire team is necessary Funding is clear Infrastructure and tooling are available 15 

Problem: CI infrastructure costs money Solution: The InnerSourceHub Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 InnerSourceHub as a platform for Inner Source Projects • Central GitLab groups for community-maintained inner source projects • Free CI pipelines and artifact repositories (centrally funded) • Simple setup • The Inner Source topic team is the maintainer of the hub • Teams channel as the central contact point 16 

Inner Source — IMPEDIMENTS Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Separate business enterprises CI infrastructure costs money Inertia and uncertainty 17 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 18 

Problem: Inertia and uncertainty Solution: An Architectural Principle Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 We provide new repositories within DB in a read-only mode for all internal employees 19 

Inner Source — IMPEDIMENTS Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Separate business enterprises CI infrastructure costs money Inertia and uncertainty 20 

Why not start as Open Source? Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Factors discouraging immediate release as an open-source project • Developer uncertainty • Trade secrets • Dependence on internal infrastructure 21 

Once a project becomes inner source, it can more easily develop into an open-source project • Example: Borg (Google) • Example: DB UI DB UI on GitHub: github.com/db-ui Inner Source as a bridge to Open Source Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 22 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 23 DB UI on GitHub: github.com/db-ui 

Glimpse into our inner source projects Examples Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 24 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Example: DB Container Lib Community Maintained About the Projekt • Collection of Dockerfiles and images • Built for production • Great variety of distributions and tools • Employee of the Month: Renovate Inner Source Patterns • Large user base • Diverse community of maintainers • Adapted for internal compliance • Dedicated Teams channel for communication within the community 25 Cost reduction Culture of Collaboration Increase Quality 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 26 

Das Projekt • Modulare GitLab CI Pipelines • ~ 200 Module • Plattformteam • Supportmodell Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Example: pipeship Team Maintained Inner Source Patterns • Bugfixing und Features direkt durch die nutzenden Teams • Issues sind transparent • Contribution Guidelines • Heavy Contributor zur DB Container Lib 27 Höhere Qualität Kultur der Zusammenarbeit 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Example: k8s-setup Community Maintained Das Projekt • Infrastructure as Code (helmfile) • Setup für Kubernetes Namespace • Abhängigkeiten zu anderen DB internen Tools und Regelwerken • Zweiteilig (Basis und ForkMe-Projekt) • Wird als Tool von unseren DevOps-Coaches eingesetzt Inner Source Patterns • Forks dienen als Beispiel für den eigenen Fork • Forks sind dank DBISL wieder Inner Source • Nutzer beteiligen sich durch Issues und Merge Requests 28 Kostenreduktion Kultur der Zusammenarbeit 

Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 Example: Microsite der Architekturgilde Das Projekt • Docs-as-Code • Verbindliche Regelwerke und unverbindliche Empfehlungen • Basiert auf Doctoolchain (danke Ralf!) Inner Source Patterns • Änderungen sind transparent in der Commithistorie nachvollziehbar • Betroffene Teams können Formulierungsverbesserungen direkt selbst per MergeRequest vorschlagen • SLA für die Reaktion auf Issues und MRs (max. 1 Woche) Team Maintained 29 Transparenz Kultur der Zusammenarbeit 

More! Carsten Hoffmann @ Inner Source Gathering Berlin | DB Systel GmbH | 12th of March 2025 InnerSource Commons innersourcecommons.org 

Contact Carsten Hoffmann Architekturschaffendes DevOps-Teammitglied Mitglied im Thementeam Inner Source [email protected] @[email protected] www.linkedin.com/in/morl99 DB Systel GmbH Jürgen-Ponto-Platz 1 | 60329 Frankfurt am Main Thank you for listening Slides and more in our blog: techstories.dbsystel.de 

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