Operator scope is what namespaces you operator will watch for Custom Resources(CR's) to be acted upon.

• Namespaced scoped (watch a single namespace)
• Cluster scoped (watch all namespaces)

The operator-sdk documentation talks about setting the watchNamespace to an empty string in the operator-sdk main.go may look something like the following.

    // check the WATCH_NAMESPACE env var to see if populated
    var watchNamespaceEnvVar = "WATCH_NAMESPACE"

    ns, found := os.LookupEnv(watchNamespaceEnvVar)
    if !found {
        return "", fmt.Errorf("%s must be set", watchNamespaceEnvVar)
    }
mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{
    Scheme:             scheme,
    MetricsBindAddress: metricsAddr,
    Port:               9443,
    LeaderElection:     enableLeaderElection,
    LeaderElectionID:   "f1c5ece8.example.com",
    Namespace:          watchNamespace, // namespaced-scope when the value is not an empty string
})

If Namespace is not set or set to an empty string your operator will already be cluster scoped.

If like me you are using OLM (Operator Lifecycle Mananger) to handle install and upgrades of your operator,you don't need change the code in main.go, OLM now handles all scoping changes for you. You only need to change the CSV and the operator group on cluster.

NOTE: v1.0.0 the Operator-sdk or greater

First you set the install installModes for AllNamespaces to true in your CSV(ClusterServiceVersion)

 installModes:
  - supported: true
    type: OwnNamespace
  - supported: true
    type: SingleNamespace
  - supported: false
    type: MultiNamespace
  - supported: true
    type: AllNamespaces 

Once this is set and deployed with OLM on cluster the only change we need is to the OperatorGroup spec. A namespaced operatorGroup spec will look like

spec:
  targetNamespaces:
  - whatever_WATCH_NAMESPACES_is

To set to Cluster scoped change the spec

spec: {}

As AllNamespaces is set in CSV you don't have to do anything else the operator will change to cluster scoped and watch all namespaces. If you don't update the operatorGroup the operator will remain namespaces scoped. So we go from namespaces scoped

To cluster scoped

Things to note the resources footprint is a little higher for the cluster scoped operator and CSV for the Operator are created in all namespaces on the cluster.