Mutating policies
The structure os mutating policies is the same as validating ones:
- They have to register
validate
andvalidate_settings
waPC functions. - The communication API used between the host and the policy is the same as that used by validating policies.
Mutating policies accept a request and can propose a mutation of the incoming
object by returning a ValidationResponse
object that looks like this:
{
"accepted": true,
"mutated_object": <object to be created>
}
The mutated_object
field contains the object the policy wants creating
in the Kubernetes cluster, serialized to JSON.
A concrete example​
Let's assume the policy received this ValidationRequest
:
{
"settings": {},
"request": {
"operation": "CREATE",
"object": {
"apiVersion": "v1",
"kind": "Pod",
"metadata": {
"name": "security-context-demo-4"
},
"spec": {
"containers": [
{
"name": "sec-ctx-4",
"image": "gcr.io/google-samples/node-hello:1.0",
"securityContext": {
"capabilities": {
"add": ["NET_ADMIN", "SYS_TIME"]
}
}
}
]
}
}
}
}
Only important field are in the request
object for this example.
This request generation happens because someone tried to create a Pod that would look like this:
apiVersion: v1
kind: Pod
metadata:
name: security-context-demo-4
spec:
containers:
- name: sec-ctx-4
image: gcr.io/google-samples/node-hello:1.0
securityContext:
capabilities:
add:
- NET_ADMIN
- SYS_TIME
Assume the policy replies with the following ValidationResponse
:
{
"accepted": true,
"mutated_object": {
"apiVersion": "v1",
"kind": "Pod",
"metadata": {
"name": "security-context-demo-4"
},
"spec": {
"containers": [
{
"name": "sec-ctx-4",
"image": "gcr.io/google-samples/node-hello:1.0",
"securityContext": {
"capabilities": {
"add": [
"NET_ADMIN",
"SYS_TIME"
],
"drop": [
"BPF"
]
}
}
}
]
}
}
}
That would lead to request acceptance, but the final Pod would look like this:
apiVersion: v1
kind: Pod
metadata:
name: security-context-demo-4
spec:
containers:
- name: sec-ctx-4
image: gcr.io/google-samples/node-hello:1.0
securityContext:
capabilities:
add:
- NET_ADMIN
- SYS_TIME
drop:
- BPF
As you can see, the policy altered the securityContext.capabilities.drop
section of the only container declared in the Pod.
The container is now dropping the BPF
capability due to the policy.
Recap​
These are the functions a mutating policy must implement:
waPC function name | Input payload | Output payload |
---|---|---|
validate | { | { |
validate_settings | { | { |