cmd: log built-in-config.yaml and merged-config.yaml

This change logs the config files on both windows and linux. It does so
by logging to STDOUT on linux and to the event log on windows.

TODO:
- Add screenshots of the log entries on pantheon
- Add tip to docs about the logs

cmd/google_cloud_ops_agent_engine/main.go

@@ -16,6 +16,7 @@ package main
 
 import (
 	"flag"
+	"io/ioutil"
 	"log"
 	"os"
 	"path/filepath"
@@ -43,5 +44,27 @@ func run() error {
 	if err := confgenerator.MergeConfFiles(*input, confDebugFolder, "linux"); err != nil {
 		return err
 	}
+	if err := logConfigFiles(filepath.Join(confDebugFolder, "built-in-config.yaml"), filepath.Join(confDebugFolder, "merged-config.yaml")); err != nil {
+		return err
+	}
 	return confgenerator.GenerateFiles(filepath.Join(confDebugFolder, "merged-config.yaml"), *service, *logsDir, *stateDir, *outDir)
 }
+
+// logConfigFiles logs the built-in and merged config files to STDOUT. These are then written by journald to var/log/syslog and so to
+// Cloud Logging once the ops-agent is running.
+func logConfigFiles(builtInConfigFile, mergedConfigFile string) error {
+	builtInConfig, err := ioutil.ReadFile(builtInConfigFile)
+	if err != nil {
+		return err
+	}
+
+	mergedConfig, err := ioutil.ReadFile(mergedConfigFile)
+	if err != nil {
+		return err
+	}
+
+	log.Printf("Built-in config: %s", builtInConfig)
+	log.Printf("Merged config: %s", mergedConfig)
+
+	return nil
+}

cmd/ops_agent_windows/run_windows.go

@@ -115,11 +115,17 @@ func (s *service) generateConfigs() error {
 	if err := confgenerator.MergeConfFiles(s.userConf, confDebugFolder, "windows"); err != nil {
 		return err
 	}
-	data, err := ioutil.ReadFile(filepath.Join(confDebugFolder, "merged-config.yaml"))
+	builtInConfig, err := ioutil.ReadFile(filepath.Join(confDebugFolder, "built-in-config.yaml"))
 	if err != nil {
 		return err
 	}
-	uc, err := confgenerator.ParseUnifiedConfigAndValidate(data, "windows")
+	mergedConfig, err := ioutil.ReadFile(filepath.Join(confDebugFolder, "merged-config.yaml"))
+	if err != nil {
+		return err
+	}
+	s.log.Info(1, fmt.Sprintf("Built-in config: %s", builtInConfig))
+	s.log.Info(1, fmt.Sprintf("Merged config: %s", mergedConfig))
+	uc, err := confgenerator.ParseUnifiedConfigAndValidate(mergedConfig, "windows")
 	if err != nil {
 		return err
 	}