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Release Notes for SCS Release 6

SCS Release 6 has been published on 2024-03-20.


Just as our previous release, Release 6 has been developed alongside a set of associated outcomes. Overall with Release 6 it becomes apparent that SCS is efficient to operate.

  • SCS is standardized
  • SCS is understandable
  • SCS enables
  • SCS is transparent
  • SCS is continuously built and tested
  • SCS is opinionated
  • SCS charters new territory

Component Versions and User-visible improvements (highlights)


The IaaS reference implementation is based on OSISM 7.0.0 and delivers the following components:


On the KaaS level, the development of the Cluster Stacks as KaaS V2 has reached a state where the approach is finally usable. With Cluster Stacks it is possible to bundle all components of Kubernetes clusters, i.e. node images, Kubernetes configuration, and cluster addons (core applications necessary to use a Kubernetes cluster) together and use the bundles to create and update clusters with one simple command.

One bundle, a Cluster Stack, can be tested extensively and is only released if both creating and upgrading clusters works smoothly. Users of these Cluster Stacks profit from the Cluster Stack Operator that works alongside with Cluster API to create and update ready-to-use clusters easily.



The Observability stack reference implementation is based on dNation Kubernetes monitoring stack v3.5.0 and delivers the following components:


  • Created a development deployment for advancement testing.
  • Simplified the installation requirements.
  • Updated the Zuul repository's README file to include complete installation instructions for Terraform an Ansible.
  • Added the clouds data into the ansible vault.
  • Created an independent ansible Zuul role.
  • Moved the custom Zuul tasks from the playbook and incorporated them into the role.
  • Moved the custom Zuul variables from the playbook into the role's variables.
  • Included the installation of Letsencrypt which adds certificates as part of the installation.
  • Added a volume on the VM for the MariaDB instance to use for continuity.
  • Added volumes on the VM for Zookeeper to use for the data snapshots and datalog.


New Features (Highlights)

Operator focused improvements

A Kubernetes engine, via k3s, has been introduced to the control plane of the IaaS reference implementation.

osism now deploys Keycloak to k3s via codecentric/keycloakx helm chart and CloudNativePG operator.

Rotation of the Octavia Amphora images has been added to the osism command. osism manage image octavia will rotate the image, which is rebuilt on a daily basis.

OpenStack Health Monitor

A new monitoring stack will replace the old openstack-health-monitor. Nevertheless, it is currently still in heavy use and has thus seen a few improvements responding to challenges observed in real-life clouds:

  • A new installation guide
  • Robustness against leaking volumes even with overloaded cinder API
  • Robustness against leaking ports from OVN LB health-monitor
  • Robustness against leftover keypairs
  • Avoid some followup errors when VM creation failed
  • Add logic to startup os-health-mon in tmux windows via systemctl --user

SCS Developer focused improvements (testbed and k8s cluster management)


  • Every component of Cluster Stacks brings a Tilt environment for local test and development
  • With csctl Cluster Stacks assets can be created and tested locally without uploading to GitHub

Preview: Domain Manager Persona

A Domain Manager role has been established in a standard draft in SCS aiming to allow self-service capabilities for customers at the identity API. Work is in progress to contribute this functionality to OpenStack Keystone and the corresponding upstream spec is currently under review. The feature is expected to be available in the next SCS release.

Preview: Central API

To improve the experience of SCS cloud customers, the idea of a "Central API" was discussed. Such API should enable customers to manage various "as-a-Service" resources. For example: OpenStack instances as well as Kubernetes clusters as well as Keycloak OAuth2 clients. Read about the trade-offs and ideas in the central-api repository and feel free to test out the POC.

Preview: Keycloak Home-IdP-discovery

To improve flexibility of onboarding new customer domains via IdP federation, SCS now deploys Keycloak with the Home-IdP-discovery plugin. The idea is, that Keystone federates out to a single Keycloak "proxy" realm (called osism in the testbed) and using the plugin, Keycloak can identify the user specific realm from an email-format login-ID. Operators can create dedicated realms for each customer and Keycloak uses internal federation to redirect from the "proxy" realm to the specific customer realm. In the customer ream they can configure IdP federation (OpenID-Connect or SAML) to their own IAM solution. The IAM section of the SCS documentation shall be extended to detail the configuration. SCS is working upstream to contribute required enhancements in the mapping of users, groups and roles from OpenID-Connect token claims to the OpenStack Keystone access management.

Upgrade/Migration notes



  • KaaSv1 is still provided with R6, but we do not intend to include it in R7 again. We want to rather focus on the feature completeness of the much more future-proof cluster-stacks.

  • In upstream OSISM the role for deploying the Tang service ( has been deprecated. We would like to encourage active contributions in this area via the deprecation, since this piece of code is currently not actively maintained nor -- to our knowledge -- actively used.

Security Fixes

During the R6 development cycle a few security issues were reported and we issued security advisories and addressed them via maintenance updates. All of these issues are also fixed in the upcoming R6 release. These include:

Other security topics were covered in our community blog as well:

Security assessment for IaaS

We invested in a range of penetration tests of the IaaS layer which resulted in valuable insight in possible improvements (e.g. applying hardening measures):

  • External pentesting of components (scanning, blackbox testing)
  • Internal pentesting of components with privileged and unprivileged system users (scanning from inside the cluster)
  • Scanning and pentesting the environment from a customer workload machine

The vision of SCS is to have continuous security assurance by adding security checks and pentesting tooling to our CI pipelines; this is currently in implementation. Next step will then be to also cover other parts (beyond the IaaS layer) of our stack with manual and then automated penetration testing.

Resolved Issues

Preview: proper scope filtering for domain list API

A fix to a bug where listing domains via Keystone API would return domains not intended to be visible to the requesting entity was contributed and merged upstream. The fix is expected to be available by the next SCS release.


The docs page has come a long way in the last 6 months. It pulls in a lot more content from the various projects and structures it in a much more accessible way. Look at the standards pages there to get an impression.

Highlighted blog posts


The documentation now contains an IAM overview document which explains current limitations for the dynamic mapping of user roles and shall be extended to explain configuration options for Operators.

Standards Conformance

The standards have evolved, increasing the amount of guarantees that software developers and operators have for workloads that work across SCS-compatible clouds. The SCS-compatible IaaS-v4 has seen improvements and better test coverage; the OSISM IaaS reference implementation fulfills all of these standards in the default configuration.

For the Kubernetes layer, we have our first set of standards almost finalized. Some of the standards for SCS-compatible KaaS-v1 are unfortunately hard to test, so we are working on adding some more tests before we cut it in stone. We aim for both KaaSv1 and v2 to fulfill the standards. (Future standards will likely not be fulfilled by KaaSv1 as it's being deprecated.)

Release Tagging

A number of repositories follow OSISM's example and use the 7.0.0 or v7.0.0 tag to denote SCS Release 6.

List of known issues & restrictions in R6


Loadbalancer service (octavia)

  • Creating loadbalancers in Cloud-in-a-Box installations fails with the error message that the VIP subnet does not exist. OSISM #890
  • When using --provider ovn with a loadbalancer health-monitor, we leak ports ovn-lb-hm-$SUBNETID in all but the VIP subnet, if we clean up the LB members before the health-monitor. This is tracked as OSISM issue #921. Deleting the health-monitor before the members or using openstack loadbalancer delete --cascade avoids this issue.
  • With amphora loadbalancers, we can end up in situations that LB deletion does no longer work due to a failover or a failed creation of the vrrp port. This is tracked in OSISM issue #925. An upstream fix exists and a backport is already underway.

We expect to resolve these issues with a maintenance update.


Some features of KaaS v1 are not available yet in KaaS v2 because they are WIP in upstream CAPO. This includes the creation of some of the optional components such as e.g. the deployment of ingress service, cert-manager, flux, harbor. More importantly, we do not yet have the handling of restrictive security groups implemented nor the ability to avoid OpenStack scheduling more than one control plane node on the same host (hypervisor).

For this reason, we are including KaaS v1 (k8s-cluster-api-provider) in the R6 release, so existing users can upgrade to the latest upstream code and continuing using it as a maintained solution while they evaluate the migration to KaaS v2 (cluster-stacks).

We will address most of the gaps during the next release cycle.

KaaS v1 should not be used for new deployments; we intend to remove it with the next release (R7).


Since Keycloak is a Java application it requires importing certificates into its certificate store. As the Keycloak pod in k3s now runs the service as non-root user, it gets more challenging to import custom certificates from arbitrary customers for IdP federation. In case this topic is interesting for specific deployments, the SCS project team would like to hear from users and discuss how to best expose such a capability.


We appreciate contribution to strategy and implementation, please join our community -- or just leave input on the github issues and PRs. Have a look at our How to contribute page.


We have had considerable help from many partners and upstream projects during the R6 development cycle. We continue to be grateful for the generous support from providers that support with infrastructure that we can use for testing and development. plusserver has been particularly generous and also helped us finding a few issues during the pre-release phase by upgrading test environments and testing them.