Rollout strategy

control/api/v1alpha1/module_types.go

@@ -20,11 +20,38 @@ type ModuleSpec struct {
 	// +optional
 	Selector *metav1.LabelSelector `json:"selector,omitempty"`
 
+	// Rollout gives the strategy for updating the module
+	// +optional
+	// +kubebuilder:default={"strategy": "all-at-once"}
+	Rollout *RolloutSpec `json:"rollout,omitempty"`
+
 	// Sync gives the configuration to sync on assigned clusters.
 	// +required
 	Sync asmv1.Sync `json:"sync"`
 }
 
+// RolloutSpec defines how the module rolls out changes when it is
+// updated itself.
+type RolloutSpec struct {
+	// Strategy names the rollout strategy to use when updating
+	// assigned clusters.
+	// +required
+	// +kubebuilder:validation:Enum=all-at-once;gradual
+	Strategy RolloutStrategyName `json:"strategy"`
+}
+
+type RolloutStrategyName string
+
+const (
+	// RolloutReplace names the strategy in which all module uses are
+	// replaced with the new definition.
+	RolloutReplace RolloutStrategyName = "all-at-once"
+	// RolloutGradual names the strategy in which module uses are
+	// updated gradually, making sure there are a limited number of
+	// clusters updating at any point.
+	RolloutGradual RolloutStrategyName = "gradual"
+)
+
 // ModuleStatus defines the observed state of Module
 type ModuleStatus struct {
 	// ObservedSync gives the spec of the Sync as most recently acted

control/config/crd/bases/fleet.squaremo.dev_modules.yaml

@@ -52,6 +52,21 @@ spec:
           spec:
             description: ModuleSpec defines the desired state of Module
             properties:
+              rollout:
+                default:
+                  strategy: all-at-once
+                description: Rollout gives the strategy for updating the module
+                properties:
+                  strategy:
+                    description: Strategy names the rollout strategy to use when updating
+                      assigned clusters.
+                    enum:
+                    - all-at-once
+                    - gradual
+                    type: string
+                required:
+                - strategy
+                type: object
               selector:
                 description: Selector gives the criteria for assigning this module
                   to an cluster. If missing, no clusters are selected. If present

docs/design/modules.md

@@ -22,3 +22,6 @@ simplest is to update one cluster at a time, and wait until it is ready before u
 The trickier questions come when you consider what to do if the assigned clusters are still in a
 rollout when you begin another, i.e., there is already at least one cluster in updating
 state. Naively, you might simply wait until there are no clusters in updating state.
+
+What about if new clusters are assigned? There is nothing to do but give them the new configuration,
+but does this count against the budget for clusters in updating state?