This epic is to develop a plan, scope and implement a form of service mesh federation that will be supportable in OpenShift Service Mesh 3 (via the sail-operator). Unlike federation with Maistra, it should be implemented using a combination of upstream Istio contributions and an independent controller (ie not in Red Hat's fork of Istio). It does not need to be a complete replacement of the Maistra federation feature, but should support some of the more common use cases. 

Details of this work are currently being captured across two documents:

• [Business background](https://docs.google.com/document/d/1cYbzRkClNOb4dIvMA6s2St4HOZisqvvqAF_tphKjyCA/edit)
• [Technical Design Proposal](https://docs.google.com/document/d/16T7GxDABKgruN9FxJzbPou99vWG0fesUWjYawv6yfak/edit?resourcekey=0-AwFFsjFH1gh9hprmxv37nQ#heading=h.xw1gqgyqs5b)

Federation is also touched upon in an upcoming blog on multi-cluster Service mesh:

https://docs.google.com/document/d/1a8rDkUcR6UZtBcnTk6li4l5NNKkDdCHLDQW5HBDZFMI/edit

Challenges with current federation:

• As it is part of Maistra.io, we do not benefit from the hardening that being in a large multi-vendor project like Istio provides.
• As it is embedded with Istio, it is difficult to maintain, as the underlying code change frequently during rebases.

• Consider... "As an upstream Istio user, if I want to federate service meshes,...such that I can include a select number(not all)  of remote services locally...how would I set this up?" Are there features that could be added to Istio to support this? If so, could we put a community proposal together?
• Refactor federation out into its own controller to be contributed as a separate project to istio-ecosystem (may have to review how it compares with Admiral, another multi-cluster project in istio-ecosystem)
• Can the use of SPIRE for trust offer a simplification? 
• Contribute CRDs upstream to make it easier to configure with upstream resources.

Related upstream issues:

• https://github.com/istio/istio/issues/48998
• https://github.com/istio/istio/issues/40589
• (Some discussion on federation related to Ambient): https://github.com/istio/istio/issues/43937
• https://github.com/istio/istio/issues/31967
• https://github.com/istio/istio/issues/31077
•  

Other similar federation implementations:
https://github.com/vmware/hamlet
Admiral