I'm using the Operator SDK to build a custom Kubernetes operator. I have created a custom resource definition and a controller using the respective Operator SDK commands:
operator-sdk add api --api-version example.com/v1alpha1 --kind=Example
operator-sdk add controller --api-version example.com/v1alpha1 --kind=Example
Within the main reconciliation loop (for the example above, the auto-generated ReconcileExample.Reconcile
method) I have some custom business logic that requires me to query the Kubernetes API for other objects of the same kind that have a certain field value. It's occurred to me that I might be able to use the default API client (that is provided by the controller) with a custom field selector:
func (r *ReconcileExample) Reconcile(request reconcile.Request) (reconcile.Result, error) {
ctx := context.TODO()
listOptions := client.ListOptions{
FieldSelector: fields.SelectorFromSet(fields.Set{"spec.someField": "someValue"}),
Namespace: request.Namespace,
}
otherExamples := v1alpha1.ExampleList{}
if err := r.client.List(ctx, &listOptions, &otherExamples); err != nil {
return reconcile.Result{}, err
}
// do stuff...
return reconcile.Result{}, nil
}
When I run the operator and create a new Example
resource, the operator fails with the following error message:
{"level":"info","ts":1563388786.825384,"logger":"controller_example","msg":"Reconciling Example","Request.Namespace":"default","Request.Name":"example-test"}
{"level":"error","ts":1563388786.8255732,"logger":"kubebuilder.controller","msg":"Reconciler error","controller":"example-controller","request":"default/example-test","error":"Index with name field:spec.someField does not exist","stacktrace":"..."}
The most important part being
Index with name field:spec.someField does not exist
I've already searched the Operator SDK's documentation on the default API client and learned a bit about the inner workings of the client, but no detailed explanation on this error or how to fix it.
What does this error message mean, and how can I create this missing index to efficiently list objects by this field value?
The default API client that is provided by the controller is a split client -- it serves Get
and List
requests from a locally-held cache and forwards other methods like Create
and Update
directly to the Kubernetes API server. This is also explained in the respective documentation:
The SDK will generate code to create a Manager, which holds a Cache and a Client to be used in CRUD operations and communicate with the API server. By default a Controller's Reconciler will be populated with the Manager's Client which is a split-client. [...] A split client reads (Get and List) from the Cache and writes (Create, Update, Delete) to the API server. Reading from the Cache significantly reduces request load on the API server; as long as the Cache is updated by the API server, read operations are eventually consistent.
To query values from the cache using a custom field selector, the cache needs to have a search index for this field. This indexer can be defined right after the cache has been set up.
To register a custom indexer, add the following code into the bootstrapping logic of the operator (in the auto-generated code, this is done directly in main
). This needs to be done after the controller manager has been instantiated (manager.New
) and also after the custom API types have been added to the runtime.Scheme
:
package main
import (
k8sruntime "k8s.io/apimachinery/pkg/runtime"
"example.com/example-operator/pkg/apis/example/v1alpha1"
// ...
)
function main() {
// ...
cache := mgr.GetCache()
indexFunc := func(obj k8sruntime.Object) []string {
return []string{obj.(*v1alpha1.Example).Spec.SomeField}
}
if err := cache.IndexField(&v1alpha1.Example{}, "spec.someField", indexFunc); err != nil {
panic(err)
}
// ...
}
When a respective indexer function is defined, field selectors on spec.someField
will work from the local cache as expected.