// Module included in the following assemblies:
// * service_mesh/v2x/ossm-deployment-models.adoc

:_mod-docs-content-type: CONCEPT
[id="ossm-about-about-migrating-to-cluster-wide_{context}"]
= About migrating to a cluster-wide mesh

In a cluster-wide mesh, one `ServiceMeshControlPlane` (SMCP) watches all of the namespaces for an entire cluster. You can migrate an existing cluster from a multitenant mesh to a cluster-wide mesh using {SMProductName} version 2.5 or later. 

[NOTE]
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If a cluster must have more than one SMCP, then you cannot migrate to a cluster-wide mesh.
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By default, a cluster-wide mesh discovers all of the namespaces that comprise a cluster. However, you can configure the mesh to access a limited set of namespaces. Namespaces do not receive sidecar injection by default. You must specify which namespaces receive sidecar injection.

Similarly, you must specify which pods receive sidecar injection. Pods that exist in a namespace that receives sidecar injection do not inherit sidecar injection. Applying sidecar injection to namespaces and to pods are separate operations.

If you change the Istio version when migrating to a cluster-wide mesh, then you must restart the applications. If you use the same Istio version, the application proxies will connect to the new SMCP for the cluster-wide mesh, and work the same way they did for a multitenant mesh.
