command/server: add support to write pprof files to the filesystem via SIGUSR2 (#20609)

* core/server: add support to write pprof files to the filesystem via SIGUSR2

* changelog

* Fix filepath join

* Use core logger

* Simplify logic

* Break on error

changelog/20609.txt

@@ -0,0 +1,4 @@
+```release-note:improvement
+command/server: Add support for dumping pprof files to the filesystem via SIGUSR2 when 
+`VAULT_PPROF_WRITE_TO_FILE=true` is set on the server.
+```

command/server.go

@@ -1719,6 +1719,44 @@ func (c *ServerCommand) Run(args []string) int {
 				c.logger.Info(fmt.Sprintf("Wrote stacktrace to: %s", f.Name()))
 				f.Close()
 			}
+
+			// We can only get pprof outputs via the API but sometimes Vault can get
+			// into a state where it cannot process requests so we can get pprof outputs
+			// via SIGUSR2.
+			if os.Getenv("VAULT_PPROF_WRITE_TO_FILE") != "" {
+				dir := ""
+				path := os.Getenv("VAULT_PPROF_FILE_PATH")
+				if path != "" {
+					if _, err := os.Stat(path); err != nil {
+						c.logger.Error("Checking pprof path failed", "error", err)
+						continue
+					}
+					dir = path
+				} else {
+					dir, err = os.MkdirTemp("", "vault-pprof")
+					if err != nil {
+						c.logger.Error("Could not create temporary directory for pprof", "error", err)
+						continue
+					}
+				}
+
+				dumps := []string{"goroutine", "heap", "allocs", "threadcreate"}
+				for _, dump := range dumps {
+					pFile, err := os.Create(filepath.Join(dir, dump))
+					if err != nil {
+						c.logger.Error("error creating pprof file", "name", dump, "error", err)
+						break
+					}
+
+					err = pprof.Lookup(dump).WriteTo(pFile, 0)
+					if err != nil {
+						c.logger.Error("error generating pprof data", "name", dump, "error", err)
+						break
+					}
+				}
+
+				c.logger.Info(fmt.Sprintf("Wrote pprof files to: %s", dir))
+			}
 		}
 	}
 	// Notify systemd that the server is shutting down