Add clustering plugin types; use latest certmagic.Storage interface

plugins.go

@@ -22,6 +22,7 @@ import (
 	"sync"
 
 	"github.com/mholt/caddy/caddyfile"
+	"github.com/mholt/certmagic"
 )
 
 // These are all the registered plugins.
@@ -73,6 +74,13 @@ func DescribePlugins() string {
 		}
 	}
 
+	if len(pl["clustering"]) > 0 {
+		str += "\nClustering plugins:\n"
+		for _, name := range pl["clustering"] {
+			str += "  " + name + "\n"
+		}
+	}
+
 	str += "\nOther plugins:\n"
 	for _, name := range pl["others"] {
 		str += "  " + name + "\n"
@@ -99,6 +107,11 @@ func ListPlugins() map[string][]string {
 		p["caddyfile_loaders"] = append(p["caddyfile_loaders"], defaultCaddyfileLoader.name)
 	}
 
+	// cluster plugins in registration order
+	for name := range clusterProviders {
+		p["clustering"] = append(p["clsutering"], name)
+	}
+
 	// List the event hook plugins
 	eventHooks.Range(func(k, _ interface{}) bool {
 		p["event_hooks"] = append(p["event_hooks"], k.(string))
@@ -443,6 +456,21 @@ func loadCaddyfileInput(serverType string) (Input, error) {
 	return caddyfileToUse, nil
 }
 
+// ClusterPluginConstructor is a function type that is used to
+// instantiate a new implementation of both certmagic.Storage
+// and certmagic.Locker, which are required for successful
+// use in cluster environments.
+type ClusterPluginConstructor func() (certmagic.Storage, error)
+
+// clusterProviders is the list of storage providers
+var clusterProviders = make(map[string]ClusterPluginConstructor)
+
+// RegisterClusterPlugin registers provider by name for facilitating
+// cluster-wide operations like storage and synchronization.
+func RegisterClusterPlugin(name string, provider ClusterPluginConstructor) {
+	clusterProviders[name] = provider
+}
+
 // OnProcessExit is a list of functions to run when the process
 // exits -- they are ONLY for cleanup and should not block,
 // return errors, or do anything fancy. They will be run with