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.io/v1alpha1
spec:
type: Universal
status:
url: https://kcp.example.com/clusters/myapp
There are different types of workspaces, and workspaces are arranged in a tree. Each type of workspace may restrict the types of its children and may restrict the types it may be a child of; a parent-child relationship is allowed if and only if the parent allows the child and the child allows the parent. The kcp binary has a built-in set of workspace types, and the admin may create objects that define additional types.
- Root Workspace is a singleton. It holds some data that applies
to all workspaces, such as the set of defined workspace types
(objects of type
WorkspaceType). - HomeRoot Workspace is normally a singleton, holding the branch of workspaces that contains the user home workspaces as descendants. Can only be a child of the root workspace, and can only have HomeBucket children.
- HomeBucket Workspace are intermediate vertices in the hierarhcy between the HomeRoot and the user home workspaces. Can be a child of the root or another HomeBucket workspace. Allowed children are home and HomeBucket workspaces.
- Home Workspace is a user's home workspace. These hold user resources such as applications with services, secrets, configmaps, deployments, etc. Can only be a child of a HomeBucket workspace.
- Organization Workspace are workspaces holding organizational data, e.g. definitions of user workspaces, roles, policies, accounting data. Can only be a child of root.
- Team Workspace can only be a child of an Organization workspace.
- Universal Workspace is a basic type of workspace with no particular nature. Has no restrictions on parent or child workspace types.
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>. A user workspace is
accessible at /clusters/root:users:<bucket-d1>:..:<bucket-dN>:<user-workspace-name>.
ClusterWorkspaces have a type. A type is defined by a WorkspaceType. 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
WorkspaceType 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 workspacetypes 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 at most ~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.
Bucket configuration options
The kcp administrator can configure:
<prefix>, which defaults toroot: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.
Warning
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 WorkspaceType 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.
As an example, the system:admin workspace exists for administrative objects
that are scoped to the local shard (e.g. lease objects for kcp internal controllers if
leader election is enabled). It is accessible via /clusters/system:admin.