Default to in-memory registry in single-binary mode

This avoids various issues of the old "mdns" default. At least for the simple
single process setup (#3134, #4597). When starting the services individually we
still default to "mdns".

ocis-pkg/registry/registry.go

@@ -3,52 +3,77 @@ package registry
 import (
 	"os"
 	"strings"
+	"sync"
 	"time"
 
 	consulr "github.com/go-micro/plugins/v4/registry/consul"
 	etcdr "github.com/go-micro/plugins/v4/registry/etcd"
 	kubernetesr "github.com/go-micro/plugins/v4/registry/kubernetes"
 	mdnsr "github.com/go-micro/plugins/v4/registry/mdns"
+	memr "github.com/go-micro/plugins/v4/registry/memory"
 	natsr "github.com/go-micro/plugins/v4/registry/nats"
 
 	"go-micro.dev/v4/registry"
 	"go-micro.dev/v4/registry/cache"
 )
 
-var (
+const (
 	registryEnv        = "MICRO_REGISTRY"
 	registryAddressEnv = "MICRO_REGISTRY_ADDRESS"
 )
 
+var (
+	once      sync.Once
+	regPlugin string
+	reg       registry.Registry
+)
+
+func Configure(plugin string) {
+	if reg == nil {
+		regPlugin = plugin
+	}
+}
+
 // GetRegistry returns a configured micro registry based on Micro env vars.
 // It defaults to mDNS, so mind that systems with mDNS disabled by default (i.e SUSE) will have a hard time
 // and it needs to explicitly use etcd. Os awareness for providing a working registry out of the box should be done.
 func GetRegistry() registry.Registry {
-	addresses := strings.Split(os.Getenv(registryAddressEnv), ",")
-
-	var r registry.Registry
-	switch os.Getenv(registryEnv) {
-	case "nats":
-		r = natsr.NewRegistry(
-			registry.Addrs(addresses...),
-		)
-	case "kubernetes":
-		r = kubernetesr.NewRegistry(
-			registry.Addrs(addresses...),
-		)
-	case "etcd":
-		r = etcdr.NewRegistry(
-			registry.Addrs(addresses...),
-		)
-	case "consul":
-		r = consulr.NewRegistry(
-			registry.Addrs(addresses...),
-		)
-	default:
-		r = mdnsr.NewRegistry()
-	}
+	once.Do(func() {
+		addresses := strings.Split(os.Getenv(registryAddressEnv), ",")
+		// prefer env of setting from Configure()
+		plugin := os.Getenv(registryEnv)
+		if plugin == "" {
+			plugin = regPlugin
+		}
 
+		switch plugin {
+		case "nats":
+			reg = natsr.NewRegistry(
+				registry.Addrs(addresses...),
+			)
+		case "kubernetes":
+			reg = kubernetesr.NewRegistry(
+				registry.Addrs(addresses...),
+			)
+		case "etcd":
+			reg = etcdr.NewRegistry(
+				registry.Addrs(addresses...),
+			)
+		case "consul":
+			reg = consulr.NewRegistry(
+				registry.Addrs(addresses...),
+			)
+		case "memory":
+			reg = memr.NewRegistry()
+		default:
+			reg = mdnsr.NewRegistry()
+		}
+		// No cache needed for in-memory registry
+		if plugin == "memory" {
+			reg = cache.New(reg, cache.WithTTL(20*time.Second))
+		}
+	})
 	// always use cached registry to prevent registry
 	// lookup for every request
-	return cache.New(r, cache.WithTTL(20*time.Second))
+	return reg
 }