CBG-4714: collect goroutine stack traces on signal

base/util.go

@@ -27,6 +27,8 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"os"
+	"path/filepath"
 	"reflect"
 	"regexp"
 	"runtime"
@@ -1831,3 +1833,45 @@ func IsRevTreeID(s string) bool {
 	}
 	return false
 }
+
+// GetStackTrace will return goroutine stack traces for all goroutines in Sync Gateway.
+func GetStackTrace() string {
+	// make 1MB buffer but if this buffer isn't big enough, runtime.Stack will
+	// return nothing, thus have 5 retires doubling the capacity each time.
+	buf := make([]byte, 1<<20)
+	for range 5 {
+		n := runtime.Stack(buf, true)
+		if n < len(buf) {
+			buf = buf[:n]
+			break
+		}
+		buf = make([]byte, 2*len(buf))
+	}
+	return string(buf)
+}
+
+// RotateProfilesIfNeeded will remove old files if there are more than
+// 10 matching the given filename pattern.
+func RotateProfilesIfNeeded(filename string) error {
+	existingFiles, err := filepath.Glob(filename)
+	if err != nil {
+		return fmt.Errorf("Error listing existing profiles in %q: %w", filename, err)
+	}
+	if len(existingFiles) <= 10 {
+		return nil
+	}
+	slices.Reverse(existingFiles)
+	var multiErr *MultiError
+	for _, profile := range existingFiles[10:] {
+		err = os.Remove(profile)
+		if err != nil {
+			multiErr = multiErr.Append(fmt.Errorf("Error removing old profile %q: %w", profile, err))
+		}
+	}
+	return multiErr.ErrorOrNil()
+}
+
+// CreateFileInDirectory will create a file in directory specified by filename.
+func CreateFileInDirectory(filename string) (*os.File, error) {
+	return os.Create(filename)
+}

rest/adminapitest/admin_api_test.go

@@ -2269,6 +2269,17 @@ func TestHandleSGCollect(t *testing.T) {
 	rest.RequireStatus(t, resp, http.StatusBadRequest)
 }
 
+func TestHandleGetStackTrace(t *testing.T) {
+	rt := rest.NewRestTester(t, nil)
+	defer rt.Close()
+
+	resp := rt.SendAdminRequest(http.MethodGet, "/_debug/stacktrace", "")
+	rest.RequireStatus(t, resp, http.StatusOK)
+	rawResponseStr := resp.Body.String()
+	assert.Contains(t, rawResponseStr, "goroutine")
+	assert.Contains(t, rawResponseStr, "handleCollectStackTrace")
+}
+
 func TestConfigRedaction(t *testing.T) {
 	base.LongRunningTest(t)
 

rest/api.go

@@ -693,6 +693,14 @@ func (h *handler) handleFgprof() error {
 	return stopFn()
 }
 
+func (h *handler) handleCollectStackTrace() error {
+
+	stackTrace := base.GetStackTrace()
+
+	h.writeText([]byte(stackTrace))
+	return nil
+}
+
 func (h *handler) handlePprofBlock() error {
 	sec, err := strconv.ParseInt(h.rq.FormValue("seconds"), 10, 64)
 	if sec <= 0 || err != nil {

rest/routing.go

@@ -316,6 +316,8 @@ func CreateAdminRouter(sc *ServerContext) *mux.Router {
 		makeHandlerWithOptions(sc, adminPrivs, []Permission{PermDevOps}, nil, (*handler).handlePprofTrace, handlerOptions{sgcollect: true})).Methods("GET", "POST")
 	r.Handle("/_debug/fgprof",
 		makeHandlerWithOptions(sc, adminPrivs, []Permission{PermDevOps}, nil, (*handler).handleFgprof, handlerOptions{sgcollect: true})).Methods("GET", "POST")
+	r.Handle("/_debug/stacktrace",
+		makeHandlerWithOptions(sc, adminPrivs, []Permission{PermDevOps}, nil, (*handler).handleCollectStackTrace, handlerOptions{sgcollect: true})).Methods("GET")
 
 	r.Handle("/_post_upgrade",
 		makeHandler(sc, adminPrivs, []Permission{PermDevOps}, nil, (*handler).handlePostUpgrade)).Methods("POST")

rest/server_context.go

@@ -20,12 +20,15 @@
 	"net"
 	"net/http"
 	"os"
+	"os/signal"
+	"path/filepath"
 	"slices"
 	"sort"
 	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
+	"syscall"
 	"time"
 
 	"github.com/KimMachineGun/automemlimit/memlimit"
@@ -59,6 +62,8 @@
 
 var allServers = []serverType{publicServer, adminServer, metricsServer, diagnosticServer}
 
+const stackFilePrefix = "sg_stack_trace_"
+
 // serverInfo represents an instance of an HTTP server from sync gateway
 type serverInfo struct {
 	server *http.Server // server is the HTTP server instance
@@ -204,9 +209,33 @@
 
 	sc.startStatsLogger(ctx)
 
+	sc.registerSignalHandlerForStackTrace(ctx)
+
 	return sc
 }
 
+// registerSignalHandlerForStackTrace will register a signal handler to capture stack traces
+// - SIGUSR1 causes Sync Gateway to record a stack trace of all running goroutines.
+func (sc *ServerContext) registerSignalHandlerForStackTrace(ctx context.Context) {
+	signalChannel := make(chan os.Signal, 1)
+	signal.Notify(signalChannel, syscall.SIGUSR1)
+
+	go func() {
+		for sig := range signalChannel {
+			base.InfofCtx(ctx, base.KeyAll, "Handling signal: %v", sig)
+			switch sig {
+			case syscall.SIGUSR1:
+				// stack trace signal received
+				currentTime := time.Now()
+				timestamp := currentTime.Format(time.RFC3339)
+				sc.logStackTraces(ctx, timestamp)
+			default:
+				// unhandled signal here
+			}
+		}
+	}()
+}
+
 func (sc *ServerContext) WaitForRESTAPIs(ctx context.Context) error {
 	timeout := 30 * time.Second
 	interval := time.Millisecond * 100
@@ -1844,6 +1873,38 @@
 
 }
 
+func (sc *ServerContext) logStackTraces(ctx context.Context, timestamp string) {
+
+	base.InfofCtx(ctx, base.KeyAll, "Collecting stack trace for all goroutines")
+	stackTrace := base.GetStackTrace()
+
+	// log to console
+	_, _ = fmt.Fprintf(os.Stderr, "Stack trace:\n%s\n", stackTrace)
+
+	filename := filepath.Join(sc.Config.Logging.LogFilePath, stackFilePrefix+timestamp+".log")
+	file, err := base.CreateFileInDirectory(filename)
+	defer func() {
+		err = file.Close()
+		if err != nil {
+			base.WarnfCtx(ctx, "Error closing stack trace file %s: %v", filename, err)
+		}
+	}()
+	if err != nil {
+		base.DebugfCtx(ctx, base.KeyAll, "Error opening stack trace file %s: %v", filename, err)
+	}
+
+	_, err = file.WriteString(fmt.Sprintf("Stack trace:\n%s\n", stackTrace))
+	if err != nil {
+		base.DebugfCtx(ctx, base.KeyAll, "Error writing stack trace to file %s: %v", filename, err)
+	}
+
+	rotatePath := filepath.Join(sc.Config.Logging.LogFilePath, stackFilePrefix+"*.log")
+	err = base.RotateProfilesIfNeeded(rotatePath)
+	if err != nil {
+		base.DebugfCtx(ctx, base.KeyAll, "Error rotating stack trace files in path %s: %v", rotatePath, err)
+	}
+}
+
 func (sc *ServerContext) logNetworkInterfaceStats(ctx context.Context) {
 
 	if err := sc.statsContext.addPublicNetworkInterfaceStatsForHostnamePort(sc.Config.API.PublicInterface); err != nil {

rest/server_context_test.go

@@ -16,6 +16,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -1062,3 +1063,30 @@ func TestDatabaseCollectionDeletedErrorState(t *testing.T) {
 	allDbs = rt.ServerContext().allDatabaseSummaries()
 	require.Len(t, allDbs, 1)
 }
+
+func TestCollectStackTraceFile(t *testing.T) {
+	base.SetUpTestLogging(t, base.LevelInfo, base.KeyAll)
+
+	tempPath := t.TempDir()
+	serverConfig := DefaultStartupConfig(tempPath)
+	serverConfig.Logging.LogFilePath = tempPath
+	ctx := t.Context()
+	serverContext := NewServerContext(ctx, &serverConfig, false)
+	defer serverContext.Close(ctx)
+
+	timeStamp := "01"
+	serverContext.logStackTraces(ctx, timeStamp)
+	require.Len(t, getFilenames(t, tempPath), 1)
+	slices.Contains(getFilenames(t, tempPath), stackFilePrefix+timeStamp+".log")
+
+	// trigger rotation and assert we don't go above 10 files
+	expectedFiles := make([]string, 0, 10)
+	for i := 2; i < 12; i++ {
+		timeStamp = fmt.Sprintf("%d", i+2)
+		serverContext.logStackTraces(ctx, timeStamp)
+		expectedFiles = append(expectedFiles, stackFilePrefix+timeStamp+".log")
+	}
+	files := getFilenames(t, tempPath)
+	require.Len(t, files, 10)
+	require.ElementsMatch(t, files, expectedFiles)
+}

rest/stats_context.go

@@ -18,7 +18,6 @@ import (
 	"path/filepath"
 	"runtime"
 	"runtime/pprof"
-	"slices"
 	"sync/atomic"
 	"time"
 
@@ -393,7 +392,7 @@ func (statsContext *statsContext) collectMemoryProfile(ctx context.Context, outp
 
 	memoryProfile := pprof.Lookup("heap")
 	filename := filepath.Join(outputDir, pprofPrefix+timestamp+".pb.gz")
-	file, err := os.Create(filename)
+	file, err := base.CreateFileInDirectory(filename)
 	defer func() {
 		err = file.Close()
 		if err != nil {
@@ -407,20 +406,8 @@ func (statsContext *statsContext) collectMemoryProfile(ctx context.Context, outp
 	if err != nil {
 		return fmt.Errorf("Error writing memory profile to %q: %w", filename, err)
 	}
-	existingProfiles, err := filepath.Glob(filepath.Join(outputDir, pprofPrefix+"*.pb.gz"))
-	if err != nil {
-		return fmt.Errorf("Error listing existing memory profiles in %q: %w", outputDir, err)
-	}
-	if len(existingProfiles) <= 10 {
-		return nil
-	}
-	slices.Reverse(existingProfiles)
-	var multiErr *base.MultiError
-	for _, profile := range existingProfiles[10:] {
-		err = os.Remove(profile)
-		if err != nil {
-			multiErr = multiErr.Append(fmt.Errorf("Error removing old memory profile %q: %w", profile, err))
-		}
-	}
-	return multiErr.ErrorOrNil()
+
+	// rotate old profiles
+	path := filepath.Join(outputDir, pprofPrefix+"*.pb.gz")
+	return base.RotateProfilesIfNeeded(path)
 }

tools-tests/sgcollect_info_test.py

@@ -72,6 +72,27 @@ def test_make_collect_logs_heap_profile(tmpdir):
         assert tasks[0].description.startswith("Contents of")
 
 
+def test_make_collect_logs_stacktrace(tmpdir):
+    with unittest.mock.patch(
+        "sgcollect.urlopen",
+        return_value=io.BytesIO(
+            '{{"logfilepath": "{logpath}"}}'.format(
+                logpath=normalize_path_for_json(tmpdir),
+            ).encode("utf-8")
+        ),
+    ):
+        stacktrace_file = tmpdir.join("sg_stack_trace.log")
+        stacktrace_file.write("foo")
+        tasks = sgcollect.make_collect_logs_tasks(
+            sg_url="fakeurl",
+            sg_config_file_path="",
+            auth_headers={},
+        )
+        assert [tasks[0].log_file] == [stacktrace_file.basename]
+        # ensure that this is not redacted task
+        assert tasks[0].description.startswith("Contents of")
+
+
 @pytest.mark.parametrize("should_redact", [True, False])
 def test_make_collect_logs_tasks_duplicate_files(should_redact, tmp_path):
     tmpdir1 = tmp_path / "tmpdir1"

tools/sgcollect.py

@@ -279,6 +279,25 @@ def make_http_client_pprof_tasks(
     return pprof_tasks
 
 
+def make_http_client_stack_trace_task(
+    sg_url: str, auth_headers: dict[str, str]
+) -> PythonTask:
+    """
+    This task uses the python http client to collect the raw stack trace data
+    """
+    stack_trace_url = "{0}/_debug/stacktrace".format(sg_url)
+
+    stack_trace_task = make_curl_task(
+        name="Collect stack trace via http client",
+        auth_headers=auth_headers,
+        url=stack_trace_url,
+        log_file="sg_stack_trace.log",
+    )
+    stack_trace_task.no_header = True
+
+    return stack_trace_task
+
+
 def to_lower_case_keys_dict(original_dict):
     result = {}
     for k, v in list(original_dict.items()):
@@ -367,6 +386,7 @@ def make_collect_logs_tasks(
         "sg_debug.log": "sg_debug.log",
         "sg_trace.log": "sg_trace.log",
         "sg_stats.log": "sg_stats.log",
+        "sg_stack_trace.log": "sg_stack_trace.log",
         "sync_gateway_access.log": "sync_gateway_access.log",
         "sync_gateway_error.log": "sync_gateway_error.log",
         "pprof.pb": "pprof.pb",
@@ -761,6 +781,10 @@ def make_sg_tasks(
 
     http_client_pprof_tasks = make_http_client_pprof_tasks(sg_url, auth_headers)
 
+    http_client_stack_trace_task = make_http_client_stack_trace_task(
+        sg_url, auth_headers
+    )
+
     # Add a task to collect Sync Gateway config
     config_tasks = make_config_tasks(
         sg_config_path, sg_url, auth_headers, should_redact
@@ -781,6 +805,7 @@ def make_sg_tasks(
             collect_logs_tasks,
             py_expvar_task,
             http_client_pprof_tasks,
+            http_client_stack_trace_task,
             config_tasks,
             status_tasks,
         ]