Add flag for go template to format host names

When using an alternate DNS like external-dns, your host names will be
different than the internal core-dns format.  This adds a flag so that
the user can specify the name format using a go template.

README.md

@@ -9,6 +9,7 @@ MinIO-Operator brings native MinIO, [MCS](https://github.com/minio/mcs), [KES](h
 | Create and delete highly available distributed MinIO clusters  | [Create a MinIO Instance](https://github.com/minio/minio-operator#create-a-minio-instance). |
 | Automatic TLS for MinIO                                        | [Automatic TLS for MinIO Instance](https://github.com/minio/minio-operator/blob/master/docs/tls.md#automatic-csr-generation). |
 | Expand an existing MinIO cluster                               | [Expand a MinIO Cluster](https://github.com/minio/minio-operator/blob/master/docs/adding-zones.md). |
+| Use a custom template for hostname discovery                   | [Custom Hostname Discovery](https://github.com/minio/minio-operator/blob/master/docs/custom-name-templates.md). |
 | Deploy MCS with MinIO cluster  | [Deploy MinIO Instance with MCS](https://github.com/minio/minio-operator/blob/master/docs/mcs.md). |
 | Deploy KES with MinIO cluster  | [Deploy MinIO Instance with KES](https://github.com/minio/minio-operator/blob/master/docs/kes.md). |
 | Deploy mc mirror  | [Deploy Mirror Instance](https://github.com/minio/minio-operator/blob/master/docs/mirror.md). |

docs/custom-name-templates.md

@@ -0,0 +1,25 @@
+# Custom Hostname Discovery
+
+[![Slack](https://slack.min.io/slack?type=svg)](https://slack.min.io)
+[![Docker Pulls](https://img.shields.io/docker/pulls/minio/k8s-operator.svg?maxAge=604800)](https://hub.docker.com/r/minio/k8s-operator)
+
+This document explains how to control the names used for host discovery.  This allows us to discover hosts using external name services, which is useful for serving with trusted certificates.
+
+## Getting Started
+
+Assuming you have a MinIO cluster with single zone, `zone-0` with 4 drives (as shown in [examples](https://github.com/minio/minio-operator/tree/master/examples)). You can dd a new zone `zone-1` with 4 drives using `kubectl patch` command.
+
+The example cluster is named minio, so the four servers will be called `minio-0`, `minio-1`, `minio-2`, and `minio-3`.  If all of your hosts are available at the domain `example.com` then you can use the `--hosts-template` flag to update discovery:
+
+```
+/minio-operator --hosts-template "{{.StatefulSet}}-{{.Ellipsis}}.example.com"
+```
+
+This will generate the discovery string `minio-{0...3}.example.com`.  The following fields are available
+| Field                 | Description |
+|-----------------------|-------------|
+| StatefulSet | The name of the instance StatefulSet (e.g. `minio`). |
+| CIService | The name of the service provided in `spec.serviceName`. |
+| HLService | The name of the headless service that is generated (e.g. `minio-hl-service`) |
+| Ellipsis | `{0...N-1}` the per-zone host numbers. |
+| Domain | The cluster domain, either `cluster.local` or the contents of the `CLUSTER_DOMAIN` environment variable. |

main.go

@@ -45,9 +45,10 @@ import (
 var Version = "DEVELOPMENT.GOGET"
 
 var (
-	masterURL    string
-	kubeconfig   string
-	checkVersion bool
+	masterURL     string
+	kubeconfig    string
+	hostsTemplate string
+	checkVersion  bool
 
 	onlyOneSignalHandler = make(chan struct{})
 	shutdownSignals      = []os.Signal{os.Interrupt, syscall.SIGTERM}
@@ -56,6 +57,7 @@ var (
 func init() {
 	flag.StringVar(&kubeconfig, "kubeconfig", "", "path to a kubeconfig. Only required if out-of-cluster")
 	flag.StringVar(&masterURL, "master", "", "the address of the Kubernetes API server. Overrides any value in kubeconfig. Only required if out-of-cluster")
+	flag.StringVar(&hostsTemplate, "hosts-template", "", "the go template to use for hostname formatting of name fields (StatefulSet, CIService, HLService, Ellipsis, Domain)")
 	flag.BoolVar(&checkVersion, "version", false, "print version")
 }
 
@@ -117,7 +119,8 @@ func main() {
 		kubeInformerFactory.Apps().V1().Deployments(),
 		kubeInformerFactory.Batch().V1().Jobs(),
 		minioInformerFactory.Operator().V1().MinIOInstances(),
-		kubeInformerFactory.Core().V1().Services())
+		kubeInformerFactory.Core().V1().Services(),
+		hostsTemplate)
 
 	mirrorController := mirror.NewController(kubeClient, controllerClient,
 		kubeInformerFactory.Batch().V1().Jobs(),

pkg/apis/operator.min.io/v1/helper.go

@@ -18,6 +18,7 @@
 package v1
 
 import (
+	"bytes"
 	"context"
 	"crypto/tls"
 	"errors"
@@ -26,6 +27,7 @@ import (
 	"net/http"
 	"path"
 	"strconv"
+	"text/template"
 	"time"
 
 	appsv1 "k8s.io/api/apps/v1"
@@ -39,6 +41,14 @@ import (
 	"github.com/minio/minio/pkg/madmin"
 )
 
+type hostsTemplateValues struct {
+	StatefulSet string
+	CIService   string
+	HLService   string
+	Ellipsis    string
+	Domain      string
+}
+
 // HasCredsSecret returns true if the user has provided a secret
 // for a MinIOInstance else false
 func (mi *MinIOInstance) HasCredsSecret() bool {
@@ -221,6 +231,36 @@ func (mi *MinIOInstance) MinIOHosts() []string {
 	return hosts
 }
 
+// TemplatedMinIOHosts returns the domain names in ellipses format created for current MinIOInstance without the service part
+func (mi *MinIOInstance) TemplatedMinIOHosts(hostsTemplate string) []string {
+	hosts := make([]string, 0)
+	tmpl, err := template.New("hosts").Parse(hostsTemplate)
+	if err != nil {
+		msg := "Invalid go template for hosts"
+		klog.V(2).Infof(msg)
+		return hosts
+	}
+	var max, index int32
+	// Create the ellipses style URL
+	for _, z := range mi.Spec.Zones {
+		max = max + z.Servers
+		data := hostsTemplateValues{
+			StatefulSet: mi.MinIOStatefulSetName(),
+			CIService:   mi.MinIOCIServiceName(),
+			HLService:   mi.MinIOHLServiceName(),
+			Ellipsis:    "{" + strconv.Itoa(int(index)) + "..." + strconv.Itoa(int(max)-1) + "}",
+			Domain:      ClusterDomain,
+		}
+		output := new(bytes.Buffer)
+		if err = tmpl.Execute(output, data); err != nil {
+			continue
+		}
+		hosts = append(hosts, output.String())
+		index = max
+	}
+	return hosts
+}
+
 // AllMinIOHosts returns the all the individual domain names relevant for current MinIOInstance
 func (mi *MinIOInstance) AllMinIOHosts() []string {
 	hosts := make([]string, 0)

pkg/controller/cluster/main-controller.go

@@ -125,6 +125,9 @@ type Controller struct {
 	// recorder is an event recorder for recording Event resources to the
 	// Kubernetes API.
 	recorder record.EventRecorder
+
+	// Use a go template to render the hosts string
+	hostsTemplate string
 }
 
 // NewController returns a new sample controller
@@ -136,7 +139,8 @@ func NewController(
 	deploymentInformer appsinformers.DeploymentInformer,
 	jobInformer batchinformers.JobInformer,
 	minioInstanceInformer informers.MinIOInstanceInformer,
-	serviceInformer coreinformers.ServiceInformer) *Controller {
+	serviceInformer coreinformers.ServiceInformer,
+	hostsTemplate string) *Controller {
 
 	// Create event broadcaster
 	// Add minio-controller types to the default Kubernetes Scheme so Events can be
@@ -164,6 +168,7 @@ func NewController(
 		serviceListerSynced:     serviceInformer.Informer().HasSynced,
 		workqueue:               queue.NewNamedRateLimitingQueue(queue.DefaultControllerRateLimiter(), "MinIOInstances"),
 		recorder:                recorder,
+		hostsTemplate:           hostsTemplate,
 	}
 
 	klog.Info("Setting up event handlers")
@@ -411,7 +416,7 @@ func (c *Controller) syncHandler(key string) error {
 			if err != nil {
 				return err
 			}
-			ss = statefulsets.NewForMinIO(mi, hlSvc.Name)
+			ss = statefulsets.NewForMinIO(mi, hlSvc.Name, c.hostsTemplate)
 			ss, err = c.kubeClientSet.AppsV1().StatefulSets(mi.Namespace).Create(ctx, ss, cOpts)
 			if err != nil {
 				return err
@@ -446,7 +451,7 @@ func (c *Controller) syncHandler(key string) error {
 				}
 			}
 
-			ss = statefulsets.NewForMinIO(mi, hlSvc.Name)
+			ss = statefulsets.NewForMinIO(mi, hlSvc.Name, c.hostsTemplate)
 			klog.V(2).Infof("Removing the existing StatefulSet %s with replicas: %d", name, *ss.Spec.Replicas)
 			if err := c.kubeClientSet.AppsV1().StatefulSets(mi.Namespace).Delete(ctx, ss.Name, metav1.DeleteOptions{}); err != nil {
 				return err
@@ -472,7 +477,7 @@ func (c *Controller) syncHandler(key string) error {
 				return err
 			}
 			klog.V(4).Infof("Updating MinIOInstance %s MinIO server version %s, to: %s", name, mi.Spec.Image, ss.Spec.Template.Spec.Containers[0].Image)
-			ss = statefulsets.NewForMinIO(mi, hlSvc.Name)
+			ss = statefulsets.NewForMinIO(mi, hlSvc.Name, c.hostsTemplate)
 			if _, err := c.kubeClientSet.AppsV1().StatefulSets(mi.Namespace).Update(ctx, ss, uOpts); err != nil {
 				return err
 			}

pkg/resources/statefulsets/minio-statefulset.go

@@ -186,15 +186,19 @@ func probes(mi *miniov1.MinIOInstance) (readiness, liveness *corev1.Probe) {
 }
 
 // Builds the MinIO container for a MinIOInstance.
-func minioServerContainer(mi *miniov1.MinIOInstance, serviceName string) corev1.Container {
+func minioServerContainer(mi *miniov1.MinIOInstance, serviceName string, hostsTemplate string) corev1.Container {
 	args := []string{"server", "--certs-dir", "/tmp/certs"}
 
 	if mi.Spec.Zones[0].Servers == 1 {
 		// to run in standalone mode we must pass the path
 		args = append(args, miniov1.MinIOVolumeMountPath)
 	} else {
 		// append all the MinIOInstance replica URLs
-		for _, h := range mi.MinIOHosts() {
+		hosts := mi.MinIOHosts()
+		if hostsTemplate != "" {
+			hosts = mi.TemplatedMinIOHosts(hostsTemplate)
+		}
+		for _, h := range hosts {
 			args = append(args, fmt.Sprintf("%s://"+h+"%s", miniov1.Scheme, mi.VolumePath()))
 		}
 	}
@@ -248,7 +252,7 @@ func getVolumesForContainer(mi *miniov1.MinIOInstance) []corev1.Volume {
 }
 
 // NewForMinIO creates a new StatefulSet for the given Cluster.
-func NewForMinIO(mi *miniov1.MinIOInstance, serviceName string) *appsv1.StatefulSet {
+func NewForMinIO(mi *miniov1.MinIOInstance, serviceName string, hostsTemplate string) *appsv1.StatefulSet {
 	// If a PV isn't specified just use a EmptyDir volume
 	var podVolumes = getVolumesForContainer(mi)
 	var replicas = mi.MinIOReplicas()
@@ -330,7 +334,7 @@ func NewForMinIO(mi *miniov1.MinIOInstance, serviceName string) *appsv1.Stateful
 		})
 	}
 
-	containers := []corev1.Container{minioServerContainer(mi, serviceName)}
+	containers := []corev1.Container{minioServerContainer(mi, serviceName, hostsTemplate)}
 
 	ss := &appsv1.StatefulSet{
 		ObjectMeta: metav1.ObjectMeta{