[Elastic Agent] Handle migration of agent_info to agent in Fleet configuration

x-pack/elastic-agent/CHANGELOG.asciidoc

@@ -73,3 +73,4 @@
 - Agent now runs the GRPC server and spawned application connect by to Agent {pull}18973[18973]
 - Rename input.type logs to logfile {pull}19360[19360]
 - Agent now installs/uninstalls Elastic Endpoint {pull}19248[19248]
+- Handle upgrade of Fleet.yml format transparently {pull}19488[19488]

x-pack/elastic-agent/pkg/agent/application/info/agent_id.go

@@ -21,13 +21,15 @@ import (
 
 // defaultAgentConfigFile is a name of file used to store agent information
 const defaultAgentConfigFile = "fleet.yml"
-const agentInfoKey = "agent"
+const agentInfoKey = "agent_info"
+const agentKey = "agent"
 
 // defaultAgentActionStoreFile is the file that will contains the action that can be replayed after restart.
 const defaultAgentActionStoreFile = "action_store.yml"
 
 type persistentAgentInfo struct {
-	ID string `json:"id" yaml:"id" config:"id"`
+	ID    string `json:"id" yaml:"id" config:"id"`
+	CapID string `json:"ID,omitempty" yaml:"ID,omitempty" config:"ID"`
 }
 
 type ioStore interface {
@@ -105,9 +107,13 @@ func getInfoFromStore(s ioStore) (*persistentAgentInfo, error) {
 			errors.TypeFilesystem)
 	}
 
-	agentInfoSubMap, found := configMap[agentInfoKey]
+	// handle migration of `agent_info` to `agent` in config
+	agentInfoSubMap, found := configMap[agentKey]
 	if !found {
-		return &persistentAgentInfo{}, nil
+		agentInfoSubMap, found = configMap[agentInfoKey]
+		if !found {
+			return &persistentAgentInfo{}, nil
+		}
 	}
 
 	cc, err := config.NewConfigFrom(agentInfoSubMap)
@@ -120,6 +126,12 @@ func getInfoFromStore(s ioStore) (*persistentAgentInfo, error) {
 		return nil, errors.New(err, "failed to unpack stored config to map")
 	}
 
+	// handle migration of agent ID from `ID` to `id` in YAML.
+	if pid.ID == "" && pid.CapID != "" {
+		pid.ID = pid.CapID
+		pid.CapID = ""
+	}
+
 	return pid, nil
 }
 
@@ -146,7 +158,15 @@ func updateAgentInfo(s ioStore, agentInfo *persistentAgentInfo) error {
 		return errors.New(err, "failed to unpack stored config to map")
 	}
 
-	configMap[agentInfoKey] = agentInfo
+	// handle migration of agent ID from `ID` to `id` in YAML.
+	if agentInfo.ID == "" && agentInfo.CapID != "" {
+		agentInfo.ID = agentInfo.CapID
+		agentInfo.CapID = ""
+	}
+
+	// set `agent` and remove old `agent_info`
+	configMap[agentKey] = agentInfo
+	delete(configMap, agentInfoKey)
 
 	r, err := yamlToReader(configMap)
 	if err != nil {

x-pack/elastic-agent/pkg/agent/application/info/agent_id_test.go

@@ -0,0 +1,75 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+package info
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/elastic/beats/v7/x-pack/elastic-agent/pkg/agent/storage"
+)
+
+func TestLoadAgentInfo(t *testing.T) {
+	defer cleanupFile()
+
+	agentInfo, err := loadAgentInfo(false)
+	require.NoError(t, err)
+	assert.NotEqual(t, "", agentInfo.ID)
+	assert.Equal(t, "", agentInfo.CapID)
+}
+
+func TestLoadAgentInfoForce(t *testing.T) {
+	defer cleanupFile()
+
+	agentInfo, err := loadAgentInfo(false)
+	require.NoError(t, err)
+	assert.NotEqual(t, "", agentInfo.ID)
+	assert.Equal(t, "", agentInfo.CapID)
+
+	agentInfo2, err := loadAgentInfo(true)
+	require.NoError(t, err)
+	assert.NotEqual(t, agentInfo.ID, agentInfo2.ID)
+}
+
+func TestLoadAgentInfoUpgrade(t *testing.T) {
+	defer cleanupFile()
+
+	// write an old agent info
+	agentConfigFile := AgentConfigFile()
+	s := storage.NewEncryptedDiskStore(agentConfigFile, []byte(""))
+	id, err := generateAgentID()
+	require.NoError(t, err)
+	err = writeOldAgentInfo(s, id)
+	require.NoError(t, err)
+
+	// load agent info, will handle upgrade
+	agentInfo, err := loadAgentInfo(false)
+	require.NoError(t, err)
+	assert.Equal(t, id, agentInfo.ID)
+	assert.Equal(t, "", agentInfo.CapID)
+}
+
+func cleanupFile() {
+	os.Remove(AgentConfigFile())
+}
+
+func writeOldAgentInfo(s ioStore, id string) error {
+	configMap := make(map[string]interface{})
+	configMap[agentInfoKey] = struct {
+		ID string `json:"ID" yaml:"ID" config:"ID"`
+	}{
+		ID: id,
+	}
+
+	r, err := yamlToReader(configMap)
+	if err != nil {
+		return err
+	}
+
+	return s.Save(r)
+}