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Motivation

In ICN, we required to share resources with multiple users and/or application. In the web enterprise segment, it is like multiple deployments team sharing the Kubernetes(K8s) cluster. In the case of Telco or Cable segment, we have multiple end users sharing the same edge compute resource. This proposal refers to the Kubernetes Multi-tenancy options and how to utilize it in ICN architecture and also to benefit Multi-tenancy use case in K8s

Goal(in Scope)

Focusing on the solution within the cluster for tenants, and working with Kubernetes SIG groups and adapt the solution in the ICN

Goal(Out of Scope)

Working in Kubernetes core or API is clearly out of the scope of these documents. There are the solutions available to provide a separate control plane to each tenant in a cluster, it is quite expensive and hard to have such a solution in a cloud-native space.

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• Soft Multitenancy tenants are trusted(means tenant obey the resource boundary between them). One tenant should not access the resource of another tenant
• Hard Multitenancy tenants can't be trusted(means any tenant can be malicious, and there must be a strong security boundary between them), So one tenant should not have access to anything from other tenants.

Requirement

1. For a service provider, a tenant is basically a group of end-user sharing the same cluster, we have to make sure that the end user resources are tracked and accountable for their consumption in a cluster
2. In a few cases, admin or end-user application is shared among multiple tenants, in such case application resource should be tracked across the cluster
3. Centralization resource quota or the allocation limits record should be maintained by admin or for the end user. For example, just a kubectl "query" to Kubernetes API should display the resource quota and policy for each end-user or tenant
4. In Edge use case, the service orchestration like ICN should get the resource details across multiple clusters by resource orchestration, should set the resource allocation for the cluster and decide the scheduling mechanism
5. User credential centralization with application orchestration

Cloud Native Multi-tenancy Proposal - Tenant controller

Cloud Native Multi-tenancy proposal reuses the Kubernetes Multi-tenancy works to bind the tenant at the service orchestration and resource orchestration level.

Kubernetes Tenant project

All the materials discussed in the following section are documented in the reference section link, and the contents are belongs to authors to respective doc

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Namespace template resource: Define like Role, RoleBinding, ResourceQuota, network policy for the namespace associated with tenant-CR

Tenant controller set up

Build the Tenant controller

The following steps explain how to run the tenant controller in kubernetes

$ go get github.com/kubernetes-sigs/multi-tenancy
$ cd $GOPATH/src/github.com/kubernetes-sigs/multi-tenancy
$ cat <<EOF > $PWD/.envrc
export PATH="`pwd`/tools/bin:$PATH"
EOF
$ source .envrc
<<Have to install additional few golang package, the project is not having vendor folder>>
$ go get github.com/golang/glog
$ go get k8s.io/client-go/kubernetes
$ go get k8s.io/client-go/kubernetes/scheme
$ go get k8s.io/client-go/plugin/pkg/client/auth/gcp
$ go get k8s.io/client-go/tools/clientcmd
$ go get github.com/hashicorp/golang-lru
$ devtk setup
$ devtk build
<<Running tenant controller>>
$ $PWD/out/tenant-controller/tenant-ctl -v=99 -kubeconfig=$HOME/.kube/config

Tenant CRD  definitions

The Tenant CRD object is defined by following CRD objects:

...

$ kubectl create -f $GOPATH/src/github.com/kubernetes-sigs/multi-tenancy/poc/tenant-controller/data/manifests/crd.yaml
$ kubectl create -f $GOPATH/src/github.com/kubernetes-sigs/multi-tenancy/poc/tenant-controller/data/manifests/rbac.yaml
<<Running tenant controller>>
$ $GOPATH/src/github.com/kubernetes-sigs/multi-tenancy/out/tenant-controller/tenant-ctl -v=99 -kubeconfig=$HOME/.kube/config

$ # kubectl get crd
NAME                                             CREATED AT
namespacetemplates.tenants.k8s.io                2019-05-01T16:34:49Z
tenants.tenants.k8s.io                           2019-05-01T16:34:49Z

$ kubectl create -f $GOPATH/src/github.com/kubernetes-sigs/multi-tenancy/poc/tenant-controller/data/manifests/sample-nstemplate.yaml
$ kubectl create -f $GOPATH/src/github.com/kubernetes-sigs/multi-tenancy/poc/tenant-controller/data/manifests/sample-tenant.yaml
$ kubectl get tenants
NAME       AGE
tenant-a   7d

$ kubectl get ns
NAME            STATUS   AGE
default         Active   42d
kube-public     Active   42d
kube-system     Active   42d
tenant-a-ns-1   Active   7d18h
tenant-a-ns-2   Active   7d18h

A closer look into tenant Object

The tenant object looks like below:

...

$ kubectl get namespacetemplate
NAME         AGE
restricted   7d

$ kubectl get namespacetemplate restricted -o yaml
apiVersion: tenants.k8s.io/v1alpha1
kind: NamespaceTemplate
metadata:
  creationTimestamp: "2019-05-01T17:37:11Z"
  generation: 1
  name: restricted
  resourceVersion: "3628408"
  selfLink: /apis/tenants.k8s.io/v1alpha1/namespacetemplates/restricted
  uid: bffbe9c8-6c37-11e9-91c3-a4bf014c3518
spec:
  templates:
  - apiVersion: rbac.authorization.k8s.io/v1
    kind: RoleBinding
    metadata:
      name: multitenancy:podsecuritypolicy
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: multitenancy:use-psp:restricted
    subjects:
    - apiGroup: rbac.authorization.k8s.io
      kind: Group
      name: system:serviceaccounts
  - apiVersion: networking.k8s.io/v1
    kind: NetworkPolicy
    metadata:
      name: multitenancy-default
    spec:
      podSelector: {}
      policyTypes:
      - Ingress
      - Egress

Resource quota proposal for the tenant CRD

A tenant-based resource quota is required to implement resource tracking in ICN. The proposal here is to reuse the tenant controller work in Kubernetes and introduce the tenant resource quota CRD on the top of tenant controller

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---
apiVersion: tenants.k8s.io/v1alpha1
  kind: TenantResourcequota
  metadata:
    name: Tenant-a-resource-quota
  spec:
    hard:
      cpu: "400"
      memory: 1000Gi
      pods: "500"
	  requests.dummy/dummyResource: 100
    scopeSelector:
      matchExpressions:
      - operator : In
        scopeName: Class
        values: ["common"]
    userResourcequota:[
                      "silver-pool-resourcequota",
					  "gold-pool-resourcequota",
					  "vfirewall-pool-resourcequota"
                   ]
---
apiVersion: v1
kind: ResourceQuota
metadata:
  name: silver-pool-resourcequota
  namespace: tenant-a-ns-2 
spec:
  hard:
    limits.cpu: "100"
    limits.memory: 250Gi
	pod: 100
    requests.dummy/dummyResource: 25
---
apiVersion: v1
kind: ResourceQuota
metadata:
  name: gold-pool-resourcequota
  namespace: tenant-a-ns-1
spec:
  hard:
    limits.cpu: "200"
    limits.memory: 700Gi
	pod:300
    requests.dummy/dummyResource: 75
---
apiVersion: v1
kind: List
items:
- apiVersion: v1
  kind: ResourceQuota
  metadata:
    name: vfirewall-v1
    namespace: tenant-a-ns-3
  spec:
    hard:
      cpu: "35"
      memory: 20Gi
      pods: "50"
    scopeSelector:
      matchExpressions:
      - operator : In
        scopeName: Firewall
        values: ["v1"]
- apiVersion: v1
  kind: ResourceQuota
  metadata:
    name: vfirewall-v3
    namespace: tenant-a-ns-3
  spec:
    hard:
      cpu: "30"
      memory: 10Gi
      pods: "15"
    scopeSelector:
      matchExpressions:
      - operator : In
        scopeName: Firewall
        values: ["v3"]

Block diagram representation of tenant resource slicing     

Image Modified

Tenant controller architecture

ICN Requirement and Tenant controller gaps

Multi-Cluster Tenant controller

<This section is incomplete and a work in progress ... needs rework and further updates ... >

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1. Design note :
• On how this would be done as Micro-service in the ONAP.
• How does interact with K8S clusters.
• How does it ensure that all the configuration is applied (rollbacks, unsuccessful edges).
• Visibility of the configuration applied on per MCTenant basis.
• When new K8S cluster is added with the label of interest, taking care of creating tenant-specific information in that edge etc..
• Extensibility (future K8S clusters having some other features that require configuration for multi-tenancy).

Open Questions:

Srinivasa Addepalli

1. Slice the tenant with the cluster "--context" 
   1. [Kural] 
      1. Tenant creation from the ONAP4K8s should be shared down to the cluster in the edge location
      2. Tenant should have kubeconfig context a slice of their namespace alone 
2. How to connect the istio Citadel certificates with Tenant? how to authenticate from the centralised location from onap4k8s to multi-cluster location?
   1. [Kural]
      
      1. Discuss so far with Istio folks and expertise, suggested that citadel certificate are bonded to namespace and specific for the application level. They are not targeted for the K8s Users
      2. For the k8s user, the certificates should be generated by the external entity and bind to the service account and the tenant as shown in the example - https://docs.bitnami.com/kubernetes/how-to/configure-rbac-in-your-kubernetes-cluster/
3. Tenant user bind to the certificates created from Citadel?
   
   1. [kural ]
      1. Initial Pathfinding show that Citadel may not be the right candidate for the K8s User certificate creation
4.  How the cluster labels are configured in ONAP? how the MC tenant controller can identify them?
   1. [ kural ]
      
      1. Adding KUD and ONAP folks here Srinivasa Addepalli Akhila Kishore @Ritu  @Kiran Itohan Ukponmwan Enyinna Ochulor
      2. Kubeconfig context should be passed from each KUD cluster to the ONAP
      3. KUD should invoke NFD immediately and enable the overall labels. And add those labels to cluster details and send back to the ONAP
      4. Cluster feature Discovery controller should be there in each Edge location cluster along with KUD, Run for each interval along with the NFD 

JIRA Story details

Reference

Kubernetes Multi-Tenancy Draft Proposal
Tenant Concept in Kubernetes

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