[controller] continuously reconcile configmaps (#118)

Now that we have a default template for configmaps that we construct for
users, we should continuously reconcile it. This will allow us to roll
out new config for M3DB over time and know that users' clusters will
pick up our changes.

This logic doesn't trigger if the user has a custom configmap.

pkg/controller/add_cluster.go

@@ -23,13 +23,17 @@ package controller
 import (
 	"errors"
 	"fmt"
+	"reflect"
 
 	myspec "github.com/m3db/m3db-operator/pkg/apis/m3dboperator/v1alpha1"
 	"github.com/m3db/m3db-operator/pkg/k8sops"
 	"github.com/m3db/m3db-operator/pkg/util/eventer"
 
 	corev1 "k8s.io/api/core/v1"
 	kerrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+	"go.uber.org/zap"
 )
 
 var (
@@ -75,14 +79,49 @@ func (c *Controller) ensureConfigMap(cluster *myspec.M3DBCluster) error {
 		return nil
 	}
 
-	cm, err := k8sops.GenerateDefaultConfigMap(cluster)
+	wantCM, err := k8sops.GenerateDefaultConfigMap(cluster)
 	if err != nil {
 		return err
 	}
 
-	_, err = c.kubeClient.CoreV1().ConfigMaps(cluster.Namespace).Create(cm)
-	if kerrors.IsAlreadyExists(err) {
+	cmClient := c.kubeClient.CoreV1().ConfigMaps(cluster.Namespace)
+
+	// Check if there is a configmap that exists. If so, overwrite it with the
+	// current templated out config. Otherwise, create one.
+	cm, err := cmClient.Get(wantCM.Name, metav1.GetOptions{})
+	if err != nil {
+		if !kerrors.IsNotFound(err) {
+			return err
+		}
+
+		// If the config doesn't exist, create it.
+		_, err := cmClient.Create(wantCM)
+		return err
+	}
+
+	// Make a copy of the configmap to not corrupt cache.
+	cm = cm.DeepCopy()
+
+	// Found an existing config map, check if we need to update its contents.
+	if reflect.DeepEqual(cm.Data, wantCM.Data) {
+		c.logger.Debug("config maps equal, nothing to do",
+			zap.String("namespace", cluster.Namespace),
+			zap.String("cluster", cluster.Name),
+		)
 		return nil
 	}
+
+	cm.Data = wantCM.Data
+	_, err = cmClient.Update(cm)
+	if err != nil {
+		c.logger.Error("error updating configmap", zap.Error(err))
+	} else {
+		c.logger.Info("updated configmap data",
+			zap.String("namespace", cluster.Namespace),
+			zap.String("cluster", cluster.Name),
+			zap.String("configmap", cm.Name),
+		)
+	}
+
 	return err
 }

pkg/controller/add_cluster_test.go

@@ -33,7 +33,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func registerValidConfigMap() error {
+func registerValidConfigMap(content string) error {
 	sw := &strings.Builder{}
 	zw := zip.NewWriter(sw)
 
@@ -42,7 +42,7 @@ func registerValidConfigMap() error {
 	if err != nil {
 		return err
 	}
-	_, err = fw.Write([]byte("my_config_data"))
+	_, err = fw.Write([]byte(content))
 	if err != nil {
 		return err
 	}
@@ -79,10 +79,9 @@ func TestEnsureConfigMap(t *testing.T) {
 	deps := newTestDeps(t, &testOpts{})
 	defer deps.cleanup()
 
-	require.NoError(t, registerValidConfigMap())
+	require.NoError(t, registerValidConfigMap("my_config_data"))
 
 	controller := deps.newController()
-
 	err := controller.ensureConfigMap(cluster)
 	assert.NoError(t, err)
 
@@ -97,3 +96,26 @@ func TestEnsureConfigMap(t *testing.T) {
 	err = controller.ensureConfigMap(cluster)
 	assert.Equal(t, errEmptyConfigMap, err)
 }
+
+func TestEnsureConfigMap_Update(t *testing.T) {
+	cluster := getFixture("cluster-simple.yaml", t)
+	deps := newTestDeps(t, &testOpts{})
+	defer deps.cleanup()
+
+	require.NoError(t, registerValidConfigMap("my_config_data"))
+
+	controller := deps.newController()
+
+	err := controller.ensureConfigMap(cluster)
+	assert.NoError(t, err)
+
+	// Change configmap data, expect to see changes reflected.
+	require.NoError(t, registerValidConfigMap("new_config_data"))
+
+	err = controller.ensureConfigMap(cluster)
+	assert.NoError(t, err)
+
+	cm, err := deps.kubeClient.CoreV1().ConfigMaps(cluster.Namespace).Get("m3db-config-map-cluster-simple", metav1.GetOptions{})
+	require.NoError(t, err)
+	assert.Equal(t, "new_config_data", cm.Data["m3.yml"])
+}