core/server: Add environment variable to write stacktrace to file (#17929)

* Add env to write stacktrace to file

* changelog

* Use os.MkdirTemp

* Properly close file

* Adding path override

* Use temp file

changelog/17929.txt

@@ -0,0 +1,4 @@
+```release-note:improvement
+core/server: Added an environment variable to write goroutine stacktraces to a 
+temporary file for SIGUSR2 signals.
+```

command/server.go

@@ -1760,6 +1760,41 @@ func (c *ServerCommand) Run(args []string) int {
 		case <-c.SigUSR2Ch:
 			logWriter := c.logger.StandardWriter(&hclog.StandardLoggerOptions{})
 			pprof.Lookup("goroutine").WriteTo(logWriter, 2)
+
+			if os.Getenv("VAULT_STACKTRACE_WRITE_TO_FILE") != "" {
+				c.logger.Info("Writing stacktrace to file")
+
+				dir := ""
+				path := os.Getenv("VAULT_STACKTRACE_FILE_PATH")
+				if path != "" {
+					if _, err := os.Stat(path); err != nil {
+						c.logger.Error("Checking stacktrace path failed", "error", err)
+						continue
+					}
+					dir = path
+				} else {
+					dir, err = os.MkdirTemp("", "vault-stacktrace")
+					if err != nil {
+						c.logger.Error("Could not create temporary directory for stacktrace", "error", err)
+						continue
+					}
+				}
+
+				f, err := os.CreateTemp(dir, "stacktrace")
+				if err != nil {
+					c.logger.Error("Could not create stacktrace file", "error", err)
+					continue
+				}
+
+				if err := pprof.Lookup("goroutine").WriteTo(f, 2); err != nil {
+					f.Close()
+					c.logger.Error("Could not write stacktrace to file", "error", err)
+					continue
+				}
+
+				c.logger.Info(fmt.Sprintf("Wrote stacktrace to: %s", f.Name()))
+				f.Close()
+			}
 		}
 	}
 	// Notify systemd that the server is shutting down