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Workspaces

Multi-tenancy is implemented through workspaces. A workspace is a Kubernetes-cluster-like HTTPS endpoint, i.e. an endpoint usual Kubernetes client tooling (client-go, controller-runtime and others) and user interfaces (kubectl, helm, web console, ...) can talk to like to a Kubernetes cluster.

Workspaces can be backed by a traditional REST store implementation through CRDs or native resources persisted in etcd. But there can be alternative implementations for special access patterns, e.g. a virtual workspace apiserver that transforms other APIs e.g. by projections (Workspace in kcp is a projection of ClusterWorkspace) or by applying visibility filters (e.g. showing all workspaces or all namespaces the current user has access to).

Workspaces are represented to the user via the Workspace kind, e.g.

kind: Workspace
apiVersion: tenancy.kcp.dev/v1beta1
spec:
  type: Universal
status:
  url: https://kcp.example.com/clusters/myapp

There is a 3-level hierarchy of workspaces:

  • Enduser Workspaces are workspaces holding enduser resources, e.g. applications with services, secrets, configmaps, deployments, etc.
  • Organization Workspaces are workspaces holding organizational data, e.g. definitions of enduser workspaces, roles, policies, accounting data.
  • Root Workspace is a singleton holding cross-organizational data and the definition of the organizations.

ClusterWorkspaces

ClusterWorkspaces define traditional etcd-based, CRD enabled workspaces, available under /clusters/<parent-workspace-name>:<cluster-workspace-name>. E.g. organization workspaces are accessible at /clusters/root:<org-name>. An enduser workspace is accessible at /clusters/<org-name>:<enduser-workspace-name>.

ClusterWorkspaces have a type. A type is defined by a ClusterWorkspaceType. A type defines initializers. They are set on new ClusterWorkspace objects and block the cluster workspace from leaving the initializing phase. Both system components and 3rd party components can use initializers to customize ClusterWorkspaces on creation, e.g. to bootstrap resources inside the workspace, or to set up permission in its parent.

A cluster workspace of type Universal is a workspace without further initialization or special properties by default, and it can be used without a corresponding ClusterWorkspaceType object (though one can be added and its initializers will be applied). ClusterWorkSpaces of type Organization are described in the next section.

Note: in order to create cluster workspaces of a given type (including Universal) you must have use permissions against the clusterworkspacetypes resources with the lower-case name of the cluster workspace type (e.g. universal). All system:authenticated users inherit this permission automatically for type Universal.

ClusterWorkspaces persisted in etcd on a shard have disjoint etcd prefix ranges, i.e. they have independent behaviour and no cluster workspace sees objects from other cluster workspaces. In contrast to namespace in Kubernetes, this includes non-namespaced objects, e.g. like CRDs where each workspace can have its own set of CRDs installed.

User Home Workspaces

User home workspaces are an optional feature of kcp. If enabled (through --enable-home-workspaces), there is a special virtual Workspace called ~ in the root workspace. It is used by kubectl ws to derive the full path to the user home workspace, similar to how Unix cd ~ move the users to their home.

The full path for a user's home workspace has a number of parts: <prefix>:(<bucket>)+<user-name>. Buckets are used to ensure that ~1000 sub-buckets or users exist in any bucket, for scaling reasons. The bucket names are deterministically derived from the user name (via some hash). Example for user adam when using default configuration: root:users:a8:f1:adam.

User home workspaces are created on-demand when they are first accessed, but this is not visible to the user, allowing the system to only incur the cost of these workspaces when they are needed. Only users of the configured home-creator-groups (default system:authenticated) will have a home workspace.

The following cluster workspace types are created internally to support User Home Workspaces:

  • homeroot: the workspace that will contain all the Home workspaces, spread across buckets. - Can contain only Homebucket workspaces
  • homebucket: the type of workspaces that will contain a subset of all home workspaces. - Can contain either Homebucket (multi-level bucketing) or Home workspaces
  • home: the ClusterWorkspace of home workspaces - can contain any type of workspaces as children (especially universal workspaces)

Bucket configuration options

The kcp administrator can configure:

  • <prefix>, which defaults to root:users
  • bucket depth, which defaults to 2
  • bucket name length, in characters, which defaults to 2

The following outlines valid configuration options. With the default setup, ~5 users or ~700 sub-buckets will be in any bucket.

NOTE: DO NOT set the bucket size to be longer than 2, as this will adversely impact performance.

User-names have (26 * [(26 + 10 + 2) * 61] * 36 = 2169648) permutations, and buckets are made up of lowercase-alpha chars. Invalid configurations break the scale limit in sub-buckets or users. Valid configurations should target having not more than ~1000 sub-buckets per bucket and at least 5 users per bucket.

Valid Configurations

length depth sub-buckets users
1 3 26 * 1 = 26 2169648 / (26)^3 = 124
1 4 26 * 1 = 26 2169648 / (26)^4 = 5
2 2 26 * 26 = 676 2169648 / (26*26)^2 = 5

Invalid Configurations

These are examples of invalid configurations and are for illustrative purposes only. In nearly all cases, the default values will be sufficient.

length depth sub-buckets users
1 1 26 * 1 = 26 2169648 / (26) = 83448
1 2 26 * 1 = 26 2169648 / (26)^2 = 3209
2 1 26 * 26 = 676 2169648 / (26*26) = 3209
2 3 26 * 26 = 676 2169648 / (26*26)^3 = .007
3 1 26 * 26 * 26 = 17576 2169648 / (262626) = 124
3 2 26 * 26 * 26 = 17576 2169648 / (262626)^2 = .007

Organization Workspaces

Organization workspaces are ClusterWorkspaces of type Organization, defined in the root workspace. Organization workspaces are accessible at /clusters/root:<org-name>.

Note: the organization ClusterWorkspaceType can only be created in the root workspace verified through admission.

Organization workspaces have standard resources (on-top of Universal workspaces) which include the ClusterWorkspace API defined through an CRD deployed during organization workspace initialization.

Root Workspace

The root workspace is a singleton in the system accessible under /clusters/root. It is not represented by a ClusterWorkspace anywhere, but shares the same properties.

Inside the root workspace at least the following resources are bootstrapped on kcp startup:

  • ClusterWorkspace CRD
  • WorkspaceShard CRD
  • Cluster CRD.

The root workspace is the only one that holds WorkspaceShard objects. WorkspaceShards are used to schedule a new ClusterWorkspace to, i.e. to select in which etcd the cluster workspace content is to be persisted.

System Workspaces

System workspaces are local to a shard and are named in the pattern system:<system-workspace-name>.

They are only accessible to a shard-local admin user and there is neither a definition via a ClusterWorkspace nor any per-request check for workspace existence.

System workspace are only accessible to a shard-local admin user, and there is neither a definition via a ClusterWorkspace, nor is there any validation of requests that the system workspace exists.

The system:admin system workspace is special as it is also accessible through / of the shard, and at /cluster/system:admin at the same time.