Create watcher subprocess with a new Console on windows

Author: pchila

internal/pkg/agent/application/upgrade/rollback.go

@@ -161,7 +161,7 @@ func InvokeWatcher(log *logger.Logger, agentExecutable string) (*exec.Cmd, error
 
 	go func() {
 		if err := cmd.Wait(); err != nil {
-			log.Infow("Upgrade Watcher exited with error", "agent.upgrade.watcher.process.pid", "agent.process.pid", agentPID, upgradeWatcherPID, "error.message", err)
+			log.Infow("Upgrade Watcher exited with error", "agent.upgrade.watcher.process.pid", agentPID, "agent.process.pid", upgradeWatcherPID, "error.message", err)
 		}
 	}()
 

internal/pkg/agent/application/upgrade/rollback_windows.go

@@ -8,8 +8,11 @@ package upgrade
 
 import (
 	"os/exec"
+	"syscall"
 	"time"
 
+	"golang.org/x/sys/windows"
+
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/paths"
 )
 
@@ -25,5 +28,23 @@ func invokeCmd(agentExecutable string) *exec.Cmd {
 		"--path.config", paths.Config(),
 		"--path.home", paths.Top(),
 	)
+
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		// Signals are sent to process groups, and child process are part of the
+		// parent's prcoess group. So to send a signal to a
+		// child process and not have it also affect ourselves
+		// (the parent process), the child needs to be created in a new
+		// process group.
+		//
+		// Creating a child with CREATE_NEW_PROCESS_GROUP disables CTLR_C_EVENT
+		// handling for the child, so the only way to gracefully stop it is with
+		// a CTRL_BREAK_EVENT signal.
+		// https://learn.microsoft.com/en-us/windows/win32/procthread/process-creation-flags
+		//
+		// Watcher process will also need a console in order to receive CTRL_BREAK_EVENT on windows.
+		// Elastic Agent main process running as a service does not have a console allocated and the watcher process will also
+		// outlive its parent during an upgrade operation so we add the CREATE_NEW_CONSOLE flag.
+		CreationFlags: windows.CREATE_NEW_PROCESS_GROUP & windows.CREATE_NEW_CONSOLE,
+	}
 	return cmd
 }

internal/pkg/agent/application/upgrade/step_relink.go

@@ -15,14 +15,14 @@ import (
 )
 
 const (
-	windows = "windows"
-	exe     = ".exe"
+	windowsOSName = "windows"
+	exe           = ".exe"
 )
 
 func changeSymlink(log *logger.Logger, topDirPath, symlinkPath, newTarget string) error {
 
 	// handle windows suffixes
-	if runtime.GOOS == windows {
+	if runtime.GOOS == windowsOSName {
 		symlinkPath += exe
 		newTarget += exe
 	}
@@ -47,7 +47,7 @@ func prevSymlinkPath(topDirPath string) string {
 	agentPrevName := agentName + ".prev"
 
 	// handle windows suffixes
-	if runtime.GOOS == windows {
+	if runtime.GOOS == windowsOSName {
 		agentPrevName = agentName + ".exe.prev"
 	}
 

internal/pkg/agent/application/upgrade/step_unpack.go

@@ -41,7 +41,7 @@ func (u *Upgrader) unpack(version, archivePath, dataDir string, flavor string) (
 	// or the extraction will be double nested
 	var unpackRes UnpackResult
 	var err error
-	if runtime.GOOS == windows {
+	if runtime.GOOS == windowsOSName {
 		unpackRes, err = unzip(u.log, archivePath, dataDir, flavor)
 	} else {
 		unpackRes, err = untar(u.log, archivePath, dataDir, flavor)