Sovereign Cloud Stack

One platform — standardized, built and operated by many.

SCS R4 released

Sovereign Cloud Stack March 22, 2023

The Sovereign Cloud Stack (SCS) project, funded by the German Federal Ministry for Economic Affairs and Climate Action to realize digital sovereignty in cloud infrastructure, releases its fifth version of the SCS reference implementation R4 on March 22, 2023. SCS contributes to the European initiative Gaia-X.

Sovereign Cloud Stack combines the best of Cloud Computing in one unified standard. SCS is built, backed, and operated by an active open-source community worldwide. Together we put users in control of their data by enabling Cloud Operators through a decentralized and federated cloud stack - leveraging true digital sovereignty to foster trust in clouds.

Defined and implemented by a growing community of over 20 companies in an open development process, based on the principles of the Four Opens, the latest version of the SCS reference implementation has been developed alongside a set of associated outcomes: SCS is standardized, federated, continuously built and tested, understandable state-of-the-art technology, and to provide operators with an excellent toolbox. Moreover, SCS helps to jumpstart the Open Operations movement, to significantly facilitate the operation of modern infrastructure.

The implemented open source components have been updated to the latest stable versions. Among others, this includes OpenStack Zed, Kubernetes Cluster API 1.3.x, Cluster API Provider for OpenStack 0.7.x, Kubernetes 1.26.x, and Ubuntu 22.04 LTS. The full release notes including a reference to the full release notes of the consumed upstream projects are available at

The SCS community works closely together with downstream users in order to address their needs and requirements in the best possible way. For instance, our Kubernetes Cluster API implementation now allows to granularly filter access to the Kubernetes API based on IP ranges, a need that came out of the development work that the Gaia-X Federation Services (GXFS) did on top of SCS.

The year of SCS standardization

The last months saw intense work in the standardization area. The foundation for this was laid by jointly defining and describing the underlying standardization process itself, known as standard SCS-0001. All further standards that apply to “SCS-compatible” conformance for the IaaS and the Container (KaaS) layer are collected in a machine-readable file and corresponding tools are provided to test compliance.

The public clouds based on the SCS reference implementation from plusserver and Noris/Wavecon are tested automatically by us and the live result is visible in the standards page.

The community has made great progress on the reference implementation with the R4 release again. This really is a good foundation for more Operators to join in. Inspired by it, we have also been able to define standards, tests for them and a testing framework to create an SCS-compatible interoperability certification. The goal for 2023 is to make the SCS initiative much broader – last not least with existing Operators that adopt the standards without necessarily consuming many of the modules of our reference implementation. — Kurt Garloff, CTO of Sovereign Cloud Stack at the Open Source Business Alliance

Information architecture

The technology stack needed to run cloud and container infrastructure is complex. One important way to make it easier is to create a framework not just for integrating the code, but also making documentation available, composing documentation from the many contributing open source projects in a consistent way.

While this effort has just started, the first results of the knowledge management work are already visible at, collecting important knowledge from the project and upstream communities to ease user’s, operator’s and contributor’s life alike. The accessibility of documentation around the OSISM testbed, the OpenStack Image Manager and the k8s cluster API provider solution have been significantly improved using this approach and more will follow.

Collaboration drives success

The SCS community has significantly grown since the previous release, both by procuring tenders as well as by stirring up intrinsic motivation. The project works closely together with related communities, such as ALASCA – Alliance for Sovereign Cloud Infrastructure, to foster standardization beyond the open reference implementation.

With new contractors joining the project’s technical teams, such as dNation working on Container Registry, Syself working on a Kubernetes as a Service integration, Cloud&Heat working on Metering of the IaaS layer, and a consortium consisting of Cloud&Heat and SecuStack working on the automation of SCS certification, the community is already preparing to set the path for upcoming releases.

Likewise, more and more operators are contributing to open operational knowledge and sharing their learnings from running cloud environments.

The development of our digitally sovereign pluscloud open has been significantly advanced by the consistent support of the Sovereign Cloud Stack community. From our perspective, this is yet another success story of the open source movement and we look forward to sharing knowledge and insights on operating these open cloud environments with the community. – Christian Schmitz, Open Source Director at plusserver GmbH

Fourth SCS cloud hits the floor

Just in time for Release 4 of the SCS project, is now the fourth provider to enter the market with its own SCS cloud infrastructure. Building on the standardized and fully open Sovereign Cloud Stack, – a project by OSISM GmbH – will offer further managed services, such as Kubernetes, for small and medium-sized enterprises.

With, we are creating a sustainable and regional managed service offering. We look forward to bringing our experience from operating the underlying cloud infrastructure back into the SCS community and thus strengthening the overall ecosystem. – Christian Berendt, CEO of OSISM GmbH

Meet Sovereign Cloud Stack in Berlin

After two successful Community Hackathons in Cologne and Nuremberg, the project invites users, developers, adopters and everybody who is affiliated to this project to gather, share knowledge, experience, and to network at our first Sovereign Cloud Stack Summit in Berlin in May. Please make sure to head over to and save your seat!

About Sovereign Cloud Stack

The Sovereign Cloud Stack (SCS) was launched in 2019 and a feasibility study was funded by the German Federal Agency for Disruptive Innovation - SPRIND. Since July 2021, SCS is a project of the Open Source Business Alliance and receives funding by the German Federal Ministry for Economic Affairs and Climate Action (BMWK). A growing community of more than 20 companies contribute to the success of Sovereign Cloud Stack. By joining forces, standards for a modern, federatable open source cloud and container platform are defined and implemented by using proven open source components. At the same time, operational knowledge and practices are transparently shared to minimize the difficulty of delivering high-quality and secure cloud offerings. Four public cloud providers use large pieces of the SCS reference implementation in action. Further setups (both public and private clouds) will soon enter production.

About the Open Source Business Alliance (OSB Alliance) e.V.

The Open Source Business Alliance (OSB Alliance) is the association of the open source industry in Germany. It represents over 200 member companies that generate more than EUR 1.7 billion1 annually in Germany. Together with scientific institutions and user organizations, the OSB Alliance is committed to sustainably anchoring the central importance of open source software and open standards for a successful digital transformation in the public awareness. This digital transformation should benefit companies, the state and society alike. In addition, innovations in the field of open source should be promoted. OSB Alliance’s goal is to establish open source as the standard in public procurement and in research and business promotion. After all, open source and open standards are essential foundations for digital sovereignty, innovative capacity and security in the digital transformation and thus the answer to one of the greatest challenges of our time.

  1. Based on a survey from September 2018.