Update filebeat registrar to use statestore (elastic#19633)

Update filebeat registrar, initialization and testing to use the
statestore as new persistent storage backend between restarts.

This PR swaps out the storage backend, adds support for migrating old registry files to the statestore, and updates existing tests in filebeat. The migration support extends the already existing migration support, supporting old registry files from the 6.x release as well (system tests start at 6.3).

filebeat/beater/filebeat.go

@@ -219,8 +219,21 @@ func (fb *Filebeat) Run(b *beat.Beat) error {
 	}
 	finishedLogger := newFinishedLogger(wgEvents)
 
+	registryMigrator := registrar.NewMigrator(config.Registry)
+	if err := registryMigrator.Run(); err != nil {
+		logp.Err("Failed to migrate registry file: %+v", err)
+		return err
+	}
+
+	stateStore, err := openStateStore(b.Info, logp.NewLogger("filebeat"), config.Registry)
+	if err != nil {
+		logp.Err("Failed to open state store: %+v", err)
+		return err
+	}
+	defer stateStore.Close()
+
 	// Setup registrar to persist state
-	registrar, err := registrar.New(config.Registry, finishedLogger)
+	registrar, err := registrar.New(stateStore, finishedLogger, config.Registry.FlushTimeout)
 	if err != nil {
 		logp.Err("Could not init registrar: %v", err)
 		return err

filebeat/beater/store.go

@@ -0,0 +1,63 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package beater
+
+import (
+	"time"
+
+	"github.com/elastic/beats/v7/filebeat/config"
+	"github.com/elastic/beats/v7/libbeat/beat"
+	"github.com/elastic/beats/v7/libbeat/logp"
+	"github.com/elastic/beats/v7/libbeat/paths"
+	"github.com/elastic/beats/v7/libbeat/statestore"
+	"github.com/elastic/beats/v7/libbeat/statestore/backend/memlog"
+)
+
+type filebeatStore struct {
+	registry      *statestore.Registry
+	storeName     string
+	cleanInterval time.Duration
+}
+
+func openStateStore(info beat.Info, logger *logp.Logger, cfg config.Registry) (*filebeatStore, error) {
+	memlog, err := memlog.New(logger, memlog.Settings{
+		Root:     paths.Resolve(paths.Data, cfg.Path),
+		FileMode: cfg.Permissions,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return &filebeatStore{
+		registry:      statestore.NewRegistry(memlog),
+		storeName:     info.Beat,
+		cleanInterval: cfg.CleanInterval,
+	}, nil
+}
+
+func (s *filebeatStore) Close() {
+	s.registry.Close()
+}
+
+func (s *filebeatStore) Access() (*statestore.Store, error) {
+	return s.registry.Get(s.storeName)
+}
+
+func (s *filebeatStore) CleanupInterval() time.Duration {
+	return s.cleanInterval
+}

filebeat/config/config.go

@@ -51,18 +51,20 @@ type Config struct {
 }
 
 type Registry struct {
-	Path         string        `config:"path"`
-	Permissions  os.FileMode   `config:"file_permissions"`
-	FlushTimeout time.Duration `config:"flush"`
-	MigrateFile  string        `config:"migrate_file"`
+	Path          string        `config:"path"`
+	Permissions   os.FileMode   `config:"file_permissions"`
+	FlushTimeout  time.Duration `config:"flush"`
+	CleanInterval time.Duration `config:"cleanup_interval"`
+	MigrateFile   string        `config:"migrate_file"`
 }
 
 var (
 	DefaultConfig = Config{
 		Registry: Registry{
-			Path:        "registry",
-			Permissions: 0600,
-			MigrateFile: "",
+			Path:          "registry",
+			Permissions:   0600,
+			MigrateFile:   "",
+			CleanInterval: 5 * time.Minute,
 		},
 		ShutdownTimeout:    0,
 		OverwritePipelines: false,