Add option to support moved filebeat modules (#9432)

If a module needs to be moved, existing configuration will stop working,
this change adds an option to mark an old module as moved to other name.

This is being considered for the movement of apache2 module to apache to
be coherent with metricbeat module (#9402).

CHANGELOG.asciidoc

@@ -73,6 +73,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 
 - Added module for parsing Google Santa logs. {pull}9540[9540]
 - Added netflow input type that supports NetFlow v1, v5, v6, v7, v8, v9 and IPFIX. {issue}9399[9399]
+- Add option to modules.yml file to indicate that a module has been moved {pull}9432[9432].
 
 *Heartbeat*
 

filebeat/fileset/modules.go

@@ -26,6 +26,7 @@ import (
 	"strings"
 
 	"github.com/pkg/errors"
+	yaml "gopkg.in/yaml.v2"
 
 	"github.com/elastic/beats/libbeat/common"
 	"github.com/elastic/beats/libbeat/kibana"
@@ -57,6 +58,12 @@ func newModuleRegistry(modulesPath string,
 			continue
 		}
 
+		// Look for moved modules
+		if module, moved := getCurrentModuleName(modulesPath, mcfg.Module); moved {
+			logp.Warn("Using old name '%s' for module '%s', please update your configuration", mcfg.Module, module)
+			mcfg.Module = module
+		}
+
 		reg.registry[mcfg.Module] = map[string]*Fileset{}
 		moduleFilesets, err := getModuleFilesets(modulesPath, mcfg.Module)
 		if err != nil {
@@ -180,7 +187,26 @@ func mcfgFromConfig(cfg *common.Config) (*ModuleConfig, error) {
 	return &mcfg, nil
 }
 
+func getCurrentModuleName(modulePath, module string) (string, bool) {
+	moduleConfigPath := filepath.Join(modulePath, module, "module.yml")
+	d, err := ioutil.ReadFile(moduleConfigPath)
+	if err != nil {
+		return module, false
+	}
+
+	var moduleConfig struct {
+		MovedTo string `yaml:"movedTo"`
+	}
+	err = yaml.Unmarshal(d, &moduleConfig)
+	if err == nil && moduleConfig.MovedTo != "" {
+		return moduleConfig.MovedTo, true
+	}
+
+	return module, false
+}
+
 func getModuleFilesets(modulePath, module string) ([]string, error) {
+	module, _ = getCurrentModuleName(modulePath, module)
 	fileInfos, err := ioutil.ReadDir(filepath.Join(modulePath, module))
 	if err != nil {
 		return []string{}, err

filebeat/fileset/modules_test.go

@@ -126,6 +126,24 @@ func TestNewModuleRegistryConfig(t *testing.T) {
 	assert.NotContains(t, reg.registry["nginx"], "error")
 }
 
+func TestMovedModule(t *testing.T) {
+	modulesPath, err := filepath.Abs("./test/moved_module")
+	assert.NoError(t, err)
+
+	configs := []*ModuleConfig{
+		&ModuleConfig{
+			Module: "old",
+			Filesets: map[string]*FilesetConfig{
+				"test": {},
+			},
+		},
+	}
+
+	reg, err := newModuleRegistry(modulesPath, configs, nil, "5.2.0")
+	assert.NoError(t, err)
+	assert.NotNil(t, reg)
+}
+
 func TestApplyOverrides(t *testing.T) {
 	falseVar := false
 	trueVar := true

filebeat/fileset/test/moved_module/old/module.yml

@@ -0,0 +1 @@
+movedTo: new