Before going through below topic lets have some questions.
- What is the main difference between a Role and a ClusterRole in AKS?
- How do you grant access to resources in a specific namespace using Roles in AKS?
- How do you grant access to resources across all namespaces in a cluster using ClusterRoles in AKS?
- How do you bind a Role to a user or a group in AKS?
- How do you bind a ClusterRole to a user or a group in AKS?
- Give an example of a situation where you would use a Role and a situation where you would use a ClusterRole in AKS.
- How do you use RoleBinding and ClusterRoleBinding to grant access to resources in AKS?
- Can a RoleBinding reference a ClusterRole? Can a ClusterRoleBinding reference a Role?
- How do you grant read-only access to all pods in an AKS cluster using RBAC?
- How do you grant read-write access to a specific namespace in an AKS cluster using RBAC?
In Kubernetes, a Role and a ClusterRole are both used to grant access to resources in a cluster. However, they have different scope and use cases.
Role: A Role is used to grant access to resources in a specific namespace. It defines a set of rules that determine what resources and actions are allowed within that namespace. A Role can be bound to a user or a group using a RoleBinding, which gives them the specific access defined in the Role.
ClusterRole: A ClusterRole is similar to a Role, but it grants access to resources across all namespaces in a cluster. It defines a set of rules that determine what resources and actions are allowed across the entire cluster. A ClusterRole can be bound to a user or a group using a ClusterRoleBinding, which gives them the specific access defined in the ClusterRole.
In Azure Kubernetes Service (AKS), you can use Role-based access control (RBAC) to grant access to resources in a cluster. Roles and ClusterRoles can be used to define the access that users and service principals have to resources in an AKS cluster.
A ClusterRole is used when you want to grant access to resources across all namespaces in a cluster, while a Role is used when you want to grant access to resources in a specific namespace.
For example, if you want to give a user read-only access to all pods in an AKS cluster, you would create a ClusterRole with the appropriate rules and bind it to the user using a ClusterRoleBinding. On the other hand, if you want to give a user read-write access to a specific namespace, you would create a Role with the appropriate rules and bind it to the user using a RoleBinding.
Example of Role
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
namespace: default
name: pod-reader
rules:
- apiGroups: [""] # "" indicates the core API group
resources: ["pods"]
verbs: ["get", "watch", "list"]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This is an example of a Kubernetes Role resource in YAML format.
The Role resource is used in conjunction with Rolebinding to grant access to resources in a namespace.
apiVersion: rbac.authorization.k8s.io/v1
This specifies that the resource is using the RBAC API version v1.
kind: Role
This specifies that the resource is a Role.
metadata:
This section contains metadata about the Role, such as its name and namespace.
namespace: default
This specifies that the Role applies to the "default" namespace.
name: pod-reader
This specifies the name of the Role as "pod-reader"
rules:
This section defines the rules for the Role, which determine what resources and actions are allowed.
apiGroups: [""]
This specifies that the rule applies to the core API group.
resources: ["pods"]
This specifies that the rule applies to "pods" resources.
verbs: ["get", "watch", "list"]
This specifies that the rule allows the "get", "watch" and "list" verbs to be performed on the "pods" resources. This means that a user or group bound to this Role will be able to get, watch and list pods in the namespace.
This Role allows read-only access to pods in the "default" namespace, this Role can be used to bind to a user or a group using Rolebinding and give them the specific access.
what is apiGroups: [""]
In Kubernetes, an API group is a set of resources and their associated endpoints. In the example you provided, apiGroups: [""] is specifying that the rule applies to the core API group.
The core API group is the set of resources and endpoints that are included in the Kubernetes API by default. These resources include things like pods, services, and replication controllers.
When you specify apiGroups: [""], it means that the rule applies to resources in the core API group. If you specify a different API group, such as apiGroups: ["batch"], the rule would only apply to resources in the batch API group.
You can also use apiGroups: ["*"] to indicate that the rule applies to all API groups.
It is important to note that some resources are extended by Kubernetes API extension, like batch API group, apps, autoscaling, and networking etc. They are not part of the core API group, thus you will have to specify the API group name if you want to grant access to those resources.
Example of ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
# "namespace" omitted since ClusterRoles are not namespaced
name: secret-reader
rules:
- apiGroups: [""]
#
# at the HTTP level, the name of the resource for accessing Secret
# objects is "secrets"
resources: ["secrets"]
verbs: ["get", "watch", "list"]This is a Kubernetes configuration file in YAML format that creates a ClusterRole named "secret-reader". The ClusterRole is used to grant access to resources across all namespaces in a cluster.
The apiVersion field specifies the version of the Kubernetes API that this configuration file uses. In this case, it's using version rbac.authorization.k8s.io/v1 of the Kubernetes API.
The kind field specifies the type of Kubernetes object that this configuration file creates. In this case, it's creating a ClusterRole object.
The metadata section contains information that identifies the ClusterRole. Since ClusterRoles are not namespaced, the "namespace" field is omitted. The name field specifies the name of the ClusterRole, in this case, "secret-reader".
The rules field specifies the access rules for this ClusterRole. The apiGroups field specifies the API group that the resources belong to. In this case, it's using the core API group represented by an empty string.
The resources field specifies the resources that this ClusterRole can access. In this case, it's granting access to "secrets" resources.
The verbs field specifies the actions that can be performed on the specified resources. In this case, the ClusterRole is granted the ability to "get", "watch" and "list" secrets.
So, this ClusterRole grants the ability to read secrets across all namespaces in the cluster using the verbs "get", "watch", and "list" on secrets resources of the core API group.
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