caddytls: Change clustering to be a plugin to the caddytls package

Should resolve the failure in
https://github.com/coredns/coredns/pull/2541.

This change is breaking to clustering plugin developers (not Caddy
users), but logical, since only the caddytls package uses CertMagic
directly (the httpserver package also uses it, but only because it also
uses the caddytls plugin); and it is early enough that no clustering
plugins really exist yet.

This will also require a change of devportal
so that it looks for a different registration function, which has moved
to the caddytls package.

caddy.go

@@ -41,12 +41,10 @@ import (
 	"strconv"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/mholt/caddy/caddyfile"
 	"github.com/mholt/caddy/telemetry"
-	"github.com/mholt/certmagic"
 )
 
 // Configurable application parameters
@@ -472,26 +470,6 @@ func (i *Instance) Caddyfile() Input {
 //
 // This function blocks until all the servers are listening.
 func Start(cdyfile Input) (*Instance, error) {
-	// set up the clustering plugin, if there is one (and there should
-	// always be one) -- this should be done exactly once, but we can't
-	// do it during init while plugins are still registering, so do it
-	// when starting the first instance)
-	if atomic.CompareAndSwapInt32(&clusterPluginSetup, 0, 1) {
-		clusterPluginName := os.Getenv("CADDY_CLUSTERING")
-		if clusterPluginName == "" {
-			clusterPluginName = "file" // name of default storage plugin as registered in caddytls package
-		}
-		clusterFn, ok := clusterProviders[clusterPluginName]
-		if !ok {
-			return nil, fmt.Errorf("unrecognized cluster plugin (was it included in the Caddy build?): %s", clusterPluginName)
-		}
-		storage, err := clusterFn()
-		if err != nil {
-			return nil, fmt.Errorf("constructing cluster plugin %s: %v", clusterPluginName, err)
-		}
-		certmagic.DefaultStorage = storage
-	}
-
 	inst := &Instance{serverType: cdyfile.ServerType(), wg: new(sync.WaitGroup), Storage: make(map[interface{}]interface{})}
 	err := startWithListenerFds(cdyfile, inst, nil)
 	if err != nil {

caddytls/setup.go

@@ -26,6 +26,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync/atomic"
 
 	"github.com/mholt/caddy"
 	"github.com/mholt/caddy/telemetry"
@@ -36,13 +37,34 @@ func init() {
 	caddy.RegisterPlugin("tls", caddy.Plugin{Action: setupTLS})
 
 	// ensure the default Storage implementation is plugged in
-	caddy.RegisterClusterPlugin("file", constructDefaultClusterPlugin)
+	RegisterClusterPlugin("file", constructDefaultClusterPlugin)
 }
 
 // setupTLS sets up the TLS configuration and installs certificates that
 // are specified by the user in the config file. All the automatic HTTPS
 // stuff comes later outside of this function.
 func setupTLS(c *caddy.Controller) error {
+	// set up the clustering plugin, if there is one (and there should always
+	// be one since this tls plugin requires it) -- this should be done exactly
+	// once, but we can't do it during init while plugins are still registering,
+	// so do it as soon as we run a setup)
+	if atomic.CompareAndSwapInt32(&clusterPluginSetup, 0, 1) {
+		clusterPluginName := os.Getenv("CADDY_CLUSTERING")
+		if clusterPluginName == "" {
+			clusterPluginName = "file" // name of default storage plugin
+		}
+		clusterFn, ok := clusterProviders[clusterPluginName]
+		if ok {
+			storage, err := clusterFn()
+			if err != nil {
+				return fmt.Errorf("constructing cluster plugin %s: %v", clusterPluginName, err)
+			}
+			certmagic.DefaultStorage = storage
+		} else {
+			return fmt.Errorf("unrecognized cluster plugin (was it included in the Caddy build?): %s", clusterPluginName)
+		}
+	}
+
 	configGetter, ok := configGetters[c.ServerType()]
 	if !ok {
 		return fmt.Errorf("no caddytls.ConfigGetter for %s server type; must call RegisterConfigGetter", c.ServerType())
@@ -423,3 +445,5 @@ func loadCertsInDir(cfg *Config, c *caddy.Controller, dir string) error {
 func constructDefaultClusterPlugin() (certmagic.Storage, error) {
 	return &certmagic.FileStorage{Path: caddy.AssetsPath()}, nil
 }
+
+var clusterPluginSetup int32 // access atomically

caddytls/tls.go

@@ -108,3 +108,19 @@ func RegisterDNSProvider(name string, provider DNSProviderConstructor) {
 	dnsProviders[name] = provider
 	caddy.RegisterPlugin("tls.dns."+name, caddy.Plugin{})
 }
+
+// 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
+	caddy.RegisterPlugin("tls.cluster."+name, caddy.Plugin{})
+}

plugins.go

@@ -22,7 +22,6 @@ import (
 	"sync"
 
 	"github.com/mholt/caddy/caddyfile"
-	"github.com/mholt/certmagic"
 )
 
 // These are all the registered plugins.
@@ -107,11 +106,6 @@ 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["clustering"], name)
-	}
-
 	// List the event hook plugins
 	eventHooks.Range(func(k, _ interface{}) bool {
 		p["event_hooks"] = append(p["event_hooks"], k.(string))
@@ -456,21 +450,6 @@ 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