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Permissions

When writing applications, you can run into a situation where your application needs to interact with on-cluster resources. In a typical Kubernetes environment you would need to go through a somewhat involved process to accomplish this. Luckily, permissions is a straight forward Acornfile definition that allows you to simplify that process.

Let's take a look at an example. Here we have a container, named API, that we want to grant CRUD operations on the FooResource in the application's namespace. For all other namespaces, we want the container to only be able to retrieve FooResources.

containers:{
api: {
// ...
permissions: {
rules: [{
verbs: [
"get",
"list",
"watch",
"create",
"update",
"patch",
"delete"
]
apiGroups: [
"api.sample.io"
]
resources: [
"fooresource"
]
}]
clusterRules: [{
verbs: [
"get",
"list",
"watch",
]
apiGroups: [
"api.sample.io"
]
resources: [
"fooresource"
]
}]
// ...
}
}
info

Standard with every container and job definition, you get a ServiceAccount with the same name as that service.

If you're curious, creating permissions in our Acornfile generates a few on-cluster resources that interact with this ServiceAccount, such as a:

  • Role with the rules we specified
  • ClusterRole with the clusterRules we specified
  • RoleBinding with the Role bound to the ServiceAccount
  • ClusterRoleBinding with the ClusterRole bound to the ServiceAccount

With this Acornfile, we accomplish our original goal. Breaking down the Acornfile a bit further, we get 5 keywords that are set to define permissions. Let's look at them one at a time.

Rules

Physically defining the permissions of your application, rules get converted into a Role that then gets attached to your application's unique ServiceAccount. This is only applicable for your application's unique namespace and, as a result, the permissions will not work in other namespaces.

ClusterRules

Similar to rules, clusterRules define permissions in the application's namespace but with the added benefit of working in other ones as well. Instead of creating a Role that gets attached to your application's ServiceAccount, you get a ClusterRole. If you would like to allow your application to perform the defined rules in any namespace on the cluster then clusterRules are the way to go.

Verbs

To define what actions your application can perform on a given resource, you define a verb. These verbs are words that allow you to declaritively define what actions your application can perform on given resources.

info

Wondering what verbs are available? Take a look!

  • get
  • list
  • watch
  • create
  • update
  • patch
  • delete
  • deletecollection

ApiGroups

When interacting with on-cluster resources, related resources are typically grouped by an apiGroup. For the context of Acorn, we need to know what apiGroup the resource we're granting permissions for is in. In our original example this was api.sample.io and others will typically be in this format.

Resources

Inside of apiGroups you'll find associated resources. With this field, you specify which resources the rules you are creating apply to. In our original example, this was foo.