Kiosk

Kiosk

https://github.com/loft-sh/kiosk

Multi-Tenancy Extension For Kubernetes

• Accounts & Account Users to separate tenants in a shared Kubernetes cluster

• Self-Service Namespace Provisioning for account users

• Account Limits to ensure quality of service and fairness when sharing a cluster

• Namespace Templates for secure tenant isolation and self-service namespace initialization

• Multi-Cluster Tenant Management for sharing a pool of clusters (coming soon)

Contents

• Why kiosk?

• Architecture

  • Workflow & Interactions

  • Custom Resources & Resource Groups

• Getting Started

  • 0. Requirements

  • 1. Install kiosk

  • 2. Configure Accounts

  • 3. Working with Spaces

  • 4. Setting Account limits

  • 5. Working with Templates

• Upgrade kiosk

• Uninstall kiosk

• Extra: User Management & Authentication

• Contributing

Why kiosk?

Kubernetes is designed as a single-tenant platform, which makes it hard for cluster admins to host multiple tenants in a single Kubernetes cluster. However, sharing a cluster has many advantages, e.g. more efficient resource utilization, less admin/configuration effort or easier sharing of cluster-internal resources among different tenants.

While there are hundreds of ways of setting up multi-tenant Kubernetes clusters and many Kubernetes distributions provide their own tenancy logic, there is no lightweight, pluggable and customizable solution that allows admins to easily add multi-tenancy capabilities to any standard Kubernetes cluster.

The Missing Multi-Tenancy Extension for Kubernetes

Kiosk/68747470733a2f2f696d672e736869656c64732e696f2f747769747465722f75726c3f7374796c653d736f6369616c2675726c3d68747470732533412532462532466769746875622e636f6d2532466b696f736b2d73682532466b696f736b

kiosk is designed to be:

• 100% Open-Source: CNCF compatible Apache 2.0 license

• Pluggable: easy to install into any existing cluster and suitable for different use cases

• Fast: emphasizing automation and self-service for tenants

• Secure: offering default configurations for different levels of tenant isolation

• Extensible: providing building blocks for higher-level Kubernetes platforms

Architecture

The core idea of kiosk is to use Kubernetes namespaces as isolated workspaces where tenant applications can run isolated from each other. To minimize admin overhead, cluster admins are supposed to configure kiosk which then becomes a self-service system for provisioning Kubernetes namespaces for tenants.

Workflow & Interactions

The following diagram shows the main actors (Cluster Admins and Account Users) as well as the most relevant Kubernetes resources and their relationships.

Click on the following links to view the description for each of the actors and kiosk components:

Details

Cluster Admin

Cluster Admins have the permission to perform CRUD operations for cluster-wide / non-namespaced resources (especially RBAC related resources as well as the custom resources Account, AccountQuota, AccountQuotaSet, and Template). Cluster Admins configure kiosk by creating and managing Accounts, AccountQuotas, AccountQuotaSets, and Templates. They can also see and configure all Spaces owned by all Accounts.

Details

Account

Every tenant is represented by an Account. Cluster Admins define and manage Accounts and assign Account Users (Users, Groups, ServiceAccounts) to Accounts - similar to assigning RBAC Roles to subjects as part of a RoleBinding configuration.

Details

Account User

Account Users perform actions within the Kubernetes cluster via API server requests while using a certain Account. Cluster Admins can assign the same Account User to multiple Accounts. Account Users have access to Spaces that belong to the Accounts they are using. If assigned the default kiosk ClusterRole, every Account User has the permission to list/get/create/delete Spaces for the respective Account, however, this can be changed via RBAC RoleBindings.

Details

Space

A Space is a non-persistent, virtual resource that represents exactly one Kubernetes namespace. Spaces have the following characteristics:

• Every space can belong up to one Account which is the owner of this Space. Ownerless Spaces are possible.

• If a user has rights to access the underlying Namespace, the user can access the Space in the same way. Hence besides Account Users, other actors (User, Group, ServiceAccount) can also access the Space if someone grants this access via additional Kubernetes RBAC.

• Every User only sees the Spaces the User has access to. This is in contrast to regular namespaces, where Users can only list all namespaces or none

• Space ownership can be changed, by changing the ownership annotation on the namespace

• During Space creation (or Space ownership changes) a RoleBinding for the owning Account is created in the corresponding Space namespace. The referenced RBAC ClusterRole can be configured in the account

• A Space can be prepopulated during creation with a predefined set of resources by configuring default Templates in the Account. Kiosk will make sure that these resources will be correctly deployed before the user gets access to the namespace.

Details

Namespace

A Namespace is a regular Kubernetes Namespace that can be accessed by anyone who has the appropriate RBAC rules to do so. Namespaces are provisioned and managed by kiosk and have a 1-to-1 relationship to the resource Space which is a custom resource of kiosk. By default, Account Users have the permission to operate within all Namespaces that are represented by Spaces which belong to one of their Accounts.

Details

Template

Templates are defined and managed by Cluster Admins. Templates are used to initialize Spaces/Namespaces with a set of Kubernetes resources (defined as manifests or as part of a Helm chart). Templates can be created using a different ClusterRole than the Account User uses, so they can be used to create resources that are not allowed to be created by actors of the Space/Namespace, e.g. to set up certain isolation resources (e.g. Network Policies, Pod Security Policies etc.). Cluster Admins can define default Templates within the Account configuration which automatically applies these templates to each Space that is created using the respective Account. Additionally, Account Users can state other non-mandatory Templates that should also be applied when creating a Space.

Details

TemplateInstance

When a Template is applied to a Space, kiosk creates a TemplateInstance to keep track of which Templates have been applied to the Space. A TemplateInstance contains information about the Template as well as about the parameters used to instantiate it. Additionally, TemplateInstances can be configured to sync with Templates, i.e. the TemplateInstance will update the resources whenever the Template changes that has been used to create these resources.

Details

AccountQuota

AccountQuotas are defined and managed by Cluster Admins. AccountQuotas define cluster-wide aggregated limits for Accounts. The resources of all Spaces/Namespaces that belong to an Account count towards the aggregated limits defined in the AccountQuota. Similar to Namespaces which can be limited by multiple ResourceQuotas, an Account can be limited by multiple AccountQuotas. If the same limit (e.g. total CPU per Account) is defined by multiple AccountQuotas, the Account will be limited according to the lowest value.

Custom Resources & Resource Groups

When installing kiosk in a Kubernetes cluster, these components will be added to the cluster:

• CRDs for Account, AccountQuota, AccountQuotaSet, Template, TemplateInstance

• Controller for kiosk Custom Resources (runs inside the cluster)

• API Server Extension (runs inside the cluster similar to the Controller)

kiosk adds two groups of resources to extend the Standard API Groups of Kubernetes:

1. Details Show List of Custom Resources

   Custom Resources: config.kiosk.sh

   Custom Resource Definitions (CRDs) for configuring kiosk. These resources are persisted in etcd just like any other Kubernetes resources and are managed by an operator which runs inside the cluster.

   • config.kiosk.sh/Account

   • config.kiosk.sh/AccountQuota

   • config.kiosk.sh/AccountQuotaSet (soon)

   • config.kiosk.sh/Template

   • config.kiosk.sh/TemplateInstance

2. Details Show List of API Extension Resources

   API Extension: tenancy.kiosk.sh

   Virtual resources which are accessible via an API Server Extension and will not be persisted in etcd. These resources are similar to views in a relational database. The benefit of providing these resources instead of only using CRDs is that we can calculate access permissions dynamically for every request. That means that it does not only allow to list, edit and manage Spaces (which map 1-to-1 to Namespaces), it also allows to show a different set of Spaces for different Account Users depending on the Accounts they are associated with or in other words: this circumvents the current limitation of Kubernetes to show filtered lists of cluster-scoped resources based on access rights.

   • tenancy.kiosk.sh/Account

   • tenancy.kiosk.sh/AccountQuota

   • tenancy.kiosk.sh/Space

   • tenancy.kiosk.sh/TemplateInstance

Getting Started

0. Requirements

0.1. CLI Tools

• kubectl: Follow this guide to install it.

• helm version 3: Follow this guide to install it.

0.2. Kubernetes Cluster

kiosk supports Kubernetes version: v1.14 and higher. Use kubectl version to determine the Server Version of your cluster. While this getting started guide should work with most Kubernetes clusters out-of-the-box, there are certain things to consider for the following types of clusters:

Details

Docker Desktop Kubernetes

All ServiceAccounts have cluster-admin role by default, which means that emulating users with ServiceAccounts is not a good idea. Use impersonation instead.

Details

Digital Ocean Kubernetes (DOKS)

All users in DOKS have cluster-admin role by default which means that when using impersonation, every user will have admin access. To see kiosk-based multi-tenancy in action, create ServiceAccounts to emulate different users.

Details

Google Kubernetes Engine (GKE)

Your kube-context will by default not have cluster-admin role. Run the following command to get your google email address and to make your user cluster admin:

# GKE: make yourself admin
GKE_USER=$(gcloud config get-value account)
kubectl create clusterrolebinding cluster-admin-binding --clusterrole cluster-admin --user $GKE_USER

0.3. Admin Context

You need a kube-context with admin rights.

If running all the following commands returns yes, you are most likely admin:

kubectl auth can-i "*" "*" --all-namespaces
kubectl auth can-i "*" namespace
kubectl auth can-i "*" clusterrole
kubectl auth can-i "*" crd

1. Install kiosk

# Install kiosk with helm v3
kubectl create namespace kiosk
helm install kiosk --repo https://charts.devspace.sh/ kiosk --namespace kiosk --atomic

To verify the installation make sure the kiosk pod is running:

$ kubectl get pod -n kiosk

NAME                     READY   STATUS    RESTARTS   AGE
kiosk-58887d6cf6-nm4qc   2/2     Running   0          1h

2. Configure Accounts

In the following steps, we will use Kubernetes user impersonation to allow you to quickly switch between cluster admin and simple account user roles. If you are cluster admin and you want to run a kubectl command as a different user, you can impersonate this user by adding the kubectl flags --as=[USER] and/or --as-group=[GROUP].

In this getting started guide, we assume two user roles:

• Cluster Admin: use your admin-context as current context (kubectl commands without -as flag)

• Account User john: use your admin-context to impersonate a user (kubectl commands with -as=john)

If you are using Digital Ocean Kubernetes (DOKS), follow this guide to simulate a user using a Service Account.

2.1. Create Account

To allow a user to create and manage namespaces, they need a kiosk account. Run the following command to create such an account for our example user john:

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/account.yaml

# Alternative: ServiceAccount as Account User (see explanation for account-sa.yaml below)
# kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/account-sa.yaml

Details

View: account.yaml

apiVersion: tenancy.kiosk.sh/v1alpha1
kind: Account
metadata:
  name: johns-account
spec:
  subjects:
  - kind: User
    name: john
    apiGroup: rbac.authorization.k8s.io

As you can see in this example, every account defines subjects which are able to use this account. In this example, there is only one subject which is a User with name john. However, Accounts can also have multiple subjects.

Subjects for kiosk Accounts are defined in the exact same way as subjects in RoleBindings. Subjects can be a combination of:

• Users

• Groups

• ServiceAccounts (see example below: account-sa.yaml)

Details

View: account-sa.yaml (alternative for ServiceAccounts, e.g. Digital Ocean Kubernetes)

If you want to assign an Account to a ServiceAccount (e.g. when using Digital Ocean Kubernetes / DOKS), please use the following alternative:

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/account-sa.yaml

apiVersion: tenancy.kiosk.sh/v1alpha1
kind: Account
metadata:
  name: johns-account
spec:
  subjects:
  - kind: ServiceAccount
    name: john
    namespace: kiosk

Learn more about User Management and Accounts in kiosk.

2.2. View Accounts

All Account Users are able to view their Account through their generated ClusterRole. Let's try this by impersonating john:

# View your own accounts as regular account user
kubectl get accounts --as=john

# View the details of one of your accounts as regular account user
kubectl get account johns-account -o yaml --as=john

3. Working with Spaces

Spaces are the virtual representation of namespaces. Each Space represents exactly one namespace. The reason why we use Spaces is that by introducing this virtual resource, we can allow users to only operate on a subset of namespaces they have access to and hide other namespaces they shouldn't see.

3.1. Allow Users To Create Spaces

By default, Account Users cannot create Spaces themselves. They can only use the Spaces/Namespaces that belong to their Accounts. That means a cluster admin would need to create the Spaces for an Account and then the Account Users could work with these Spaces/Namespaces.

To allow all Account Users to create Spaces for their own Accounts, create the following RBAC ClusterRoleBinding:

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/rbac-creator.yaml

Details

View: rbac-creator.yaml

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: kiosk-creator
subjects:
- kind: Group
  name: system:authenticated
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: ClusterRole
  name: kiosk-edit
  apiGroup: rbac.authorization.k8s.io

Of course, you can also adjust this ClusterRoleBinding in a way that only certain subjects/users can create Spaces for their Accounts. Just modify the subjects section.

3.2. Create Spaces

After granting Account Users the right to create Spaces for their Accounts (see ClusterRoleBinding in 3.1.), all Account Users are able to create Spaces. Let's try this by impersonating john:

kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/space.yaml --as=john

Details

View: space.yaml

apiVersion: tenancy.kiosk.sh/v1alpha1
kind: Space
metadata:
  name: johns-space
spec:
  # spec.account can be omitted if the current user only belongs to a single account
  account: johns-account

As you can see in this example, every Space belongs to exactly one Account which is referenced by spec.account.

3.3. View Spaces

Let's take a look at the Spaces of the Accounts that User john owns by impersonating this user:

# List all Spaces as john:
kubectl get spaces --as=john

# Get the defails of one of john's Spaces:
kubectl get space johns-space -o yaml --as=john

3.4. Use Spaces

Every Space is the virtual representation of a regular Kubernetes Namespace. That means we can use the associated Namespace of our Spaces just like any other Namespace.

Let's impersonate john again and create an nginx deployment inside johns-space:

kubectl apply -n johns-space --as=john -f https://raw.githubusercontent.com/kubernetes/website/master/content/en/examples/application/deployment.yaml

That's great, right? A user that did not have any access to the Kubernetes cluster, is now able to create Namespaces on-demand and gets restricted access to these Namespaces automatically.

3.5. Create Deletable Spaces

To allow Account Users to delete all Spaces/Namespace that they create, you need to set the spec.space.clusterRole field in the Account to kiosk-space-admin.

When creating a Space, kiosk creates the according Namespace for the Space and then creates a RoleBinding within this Namespace which binds the standard Kubernetes ClusterRole admin to every Account User (i.e. all subjects listed in the Account). While this ClusterRole allows full access to this Namespace, it does not allow to delete the Space/Namespace. (The verb delete is missing in the default admin clusterrole)

As john can be User of multiple Accounts, let's create a second Account which allows john to delete Spaces/Namespaces that belong to this Account:

# Run this as cluster admin:
# Create Account johns-account-deletable-spaces
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/account-deletable-spaces.yaml

Details

View: account-deletable-spaces.yaml

apiVersion: tenancy.kiosk.sh/v1alpha1
kind: Account
metadata:
  name: johns-account-deletable-spaces
spec:
  space:
    clusterRole: kiosk-space-admin
  subjects:
  - kind: User
    name: john
    apiGroup: rbac.authorization.k8s.io

If you are using ServiceAccounts instead of impersonation, adjust the subjects section of this Account similar to account-sa.yaml in 2.1.

Now, let's create a Space for this Account:

# Run this as john:
# Create Space johns-space-deletable
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/space-deletable.yaml --as=john

Details

View: space-deletable.yaml

apiVersion: tenancy.kiosk.sh/v1alpha1
kind: Space
metadata:
  name: johns-space-deletable
spec:
  account: johns-account-deletable-spaces

3.6. Delete Spaces

If a Space belongs to an Account that allows Account Users to delete such Spaces, an Account User can simply delete the Space using kubectl:

kubectl get spaces --as=john
kubectl delete space johns-space-deletable --as=john
kubectl get spaces --as=john

Deleting a Space also deletes the underlying Namespace.

3.7. Defaults for Spaces

kiosk provides the spec.space.spaceTemplate option for Accounts which lets admins define defaults for new Spaces of an Account. The following example creates the Account account-default-space-metadata which defines default labels and annotations for all Spaces created with this Account:

# Run this as cluster admin:
# Create Account johns-account-default-space-metadata
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/account-default-space-metadata.yaml

Details

View: account-default-space-metadata.yaml

apiVersion: tenancy.kiosk.sh/v1alpha1
kind: Account
metadata:
  name: johns-account-default-space-metadata
spec:
  space:
    clusterRole: kiosk-space-admin
    spaceTemplate:
      metadata:
        labels:
          some-label: "label-value"
          some--other-label: "other-label-value"
        annotations:
          "space-annotation-1": "annotation-value-1"
          "space-annotation-2": "annotation-value-2"
  subjects:
  - kind: User
    name: john
    apiGroup: rbac.authorization.k8s.io

4. Setting Account Limits

With kiosk, you have two options to limit Accounts:

• Limit Number of Spaces for an Account

• Set Account Quotas = maximum values for resources aggregated across all Spaces of an Account (e.g. total number of Pods combined in all Spaces)

4.1. Limit Number of Spaces

By setting the spec.space.limit in an Account, Cluster Admins can limit the number of Spaces that Account Users can create for a certain Account.

Let's run the following command to update the existing Account johns-account and specify spec.space.limit: 2:

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/account-space-limit.yaml

Details

View: account-space-limit.yaml

apiVersion: tenancy.kiosk.sh/v1alpha1
kind: Account
metadata:
  name: johns-account
spec:
  space:
    limit: 2
  subjects:
  - kind: User
    name: john
    apiGroup: rbac.authorization.k8s.io

Now, let's try to create more than 2 Spaces (note that you may have already created a Space for this Account during earlier steps of this getting started guide):

# List existing spaces:
kubectl get spaces --as=john

# Create space-2 => should work if you had only one Space for this Account so far
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/space-2.yaml --as=john

# Create space-3 => should result in an error
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/space-3.yaml --as=john

4.2. AccountQuotas

AccountQuotas allow you to define limits for an Account which are aggregated across all Spaces of this Account.

Let's create an AccountQuota for johns-account which will set the aggregated number of Pods across all Spaces to 2 and the aggregated maximum of limits.cpu across all Pods in all Spaces to 4 CPU Cores (see Kubernetes resource limits):

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/accountquota.yaml

Details

View: accountquota.yaml

apiVersion: config.kiosk.sh/v1alpha1
kind: AccountQuota
metadata:
  name: default-user-limits
spec:
  account: johns-account
  quota:
    hard:
      pods: "2"
      limits.cpu: "4"

AccountQuotas allow you to restrict the same resources as Kubernetes ResourceQuotas but unlike ResourceQuotas, AccountQuotas are not restricted to a single Namespace. Instead, AccountQuotas add up all used resources across all Spaces of an Account to generate an aggregated value which is then compared to the max value defined in the AccountQuota.

If there are multiple AccountQuotas referencing the same Account via spec.account, kiosk merges the Quotas. In case multiple AccountQuotas define different limits for the same resource type, kiosk uses the lowest value.

5. Working with Templates

Templates in kiosk are used to initialize Namespaces and share common resources across namespaces (e.g. secrets). When creating a Space, kiosk will use these Templates to populate the newly created Namespace for this Space. Templates:

• can either contain one or more Kubernetes manifests or alternatively a Helm chart

• are being tracked by TemplateInstances in each Namespace they are applied to

• can contain parameters such as ${NAMESPACE} or ${MY_PARAMETER} that can be specified within an TemplateInstance

5.1. Manifest Templates

The easiest option to define a Template is by specifying an array of Kubernetes manifests which should be applied when the Template is being instantiated.

The following command will create a Template called space-restrictions which defined 2 manifests, a Network Policy which will make sure that the users of this Space/Namespace cannot create privileged containers and a LimitRange for default CPU limits of containers in this Namespace:

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/template-manifests.yaml

Details

View: template-manifests.yaml

apiVersion: config.kiosk.sh/v1alpha1
kind: Template
metadata:
  name: space-restrictions
# This section defines parameters that can be used for this template
# Can be used in resources.manifests and resources.helm.values
parameters:
# Name of the parameter
- name: DEFAULT_CPU_LIMIT
  # The default value of the parameter
  value: "1"
- name: DEFAULT_CPU_REQUESTS
  value: "0.5"
  # If a parameter is required the template instance will need to set it
  # required: true
  # Make sure only values are entered for this parameter
  validation: "^[0-9]*\\.?[0-9]+$"
resources:
  manifests:
  - kind: NetworkPolicy
    apiVersion: networking.k8s.io/v1
    metadata:
      name: deny-cross-ns-traffic
    spec:
      podSelector:
        matchLabels:
      ingress:
      - from:
        - podSelector: {}
  - apiVersion: v1
    kind: LimitRange
    metadata:
      name: space-limit-range
    spec:
      limits:
      - default:
          # Use the DEFAULT_CPU_LIMIT parameter here and
          # parse it as json, which renders the "1" as 1.
          cpu: "${{DEFAULT_CPU_LIMIT}}"
        defaultRequest:
          cpu: "${{DEFAULT_CPU_REQUESTS}}"
        type: Container

5.2. Helm Chart Templates

Instead of manifests, a Template can specify a Helm chart that will be installed (using helm template) when the Template is being instantiated. Let's create a Template called redis which installs the stable/redis Helm chart:

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/template-helm.yaml

Details

View: template-helm.yaml

apiVersion: config.kiosk.sh/v1alpha1
kind: Template
metadata:
  name: redis
resources:
  helm:
    releaseName: redis
    chart:
      repository:
        name: redis
        repoUrl: https://kubernetes-charts.storage.googleapis.com
    values: |
      redisPort: 6379
      # Use a predefined parameter here
      myOtherValue: ${NAMESPACE}

5.3. Using Templates

By default, only admins can list Templates. To allow users to view templates, you need to set up RBAC accordingly. Run the following code to allow every cluster user to list and view all Templates:

# Run this as cluster admin:
kubectl apply -f https://raw.githubusercontent.com/kiosk-sh/kiosk/master/examples/rbac-template-viewer.yaml

Details

View: rbac-template-viewer.yaml

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: kiosk-template-view
rules:
- apiGroups:
  - config.kiosk.sh
  resources:
  - templates
  verbs:
  - get
  - list
  - watch