validate decoded bootstrap data does not exceed the user_data byte li…

…mit according to the Linode API

controller/linodemachine_controller_helpers.go

@@ -41,6 +41,10 @@ import (
 	infrav1alpha1 "github.com/linode/cluster-api-provider-linode/api/v1alpha1"
 )
 
+// Size limit in bytes on the decoded metadata.user_data for cloud-init
+// The decoded user_data must not exceed 16384 bytes per the Linode API
+const maxBootstrapDataBytes = 16384
+
 func (*LinodeMachineReconciler) newCreateConfig(ctx context.Context, machineScope *scope.MachineScope, tags []string, logger logr.Logger) (*linodego.InstanceCreateOptions, error) {
 	var err error
 
@@ -61,6 +65,12 @@ func (*LinodeMachineReconciler) newCreateConfig(ctx context.Context, machineScop
 
 		return nil, err
 	}
+	if len(bootstrapData) > maxBootstrapDataBytes {
+		err = errors.New("bootstrap data too large")
+		logger.Error(err, "decoded bootstrap data exceeds size limit of %d bytes", maxBootstrapDataBytes)
+
+		return nil, err
+	}
 	createConfig.Metadata = &linodego.InstanceMetadataOptions{
 		UserData: b64.StdEncoding.EncodeToString(bootstrapData),
 	}