storage: prevent node from restarting after consistency check fatal

Many deployments auto-restart crashed nodes unconditionally.  As a
result, we are often pulled into inconsistency failures relatively late,
which results in a loss of information (in particular if the source of
the problem turns out to be one of the nodes that did not actually
crash); if the node that crashes *is* the one with the problem,
restarting it lets it serve data again (until the next time the
consistency checker nukes it), which is bad as well.

This commit introduces a "death rattle" - if a node is told to terminate
as the result of a consistency check, it will write a marker file that
prevents subsequent restarts of the node with an informative message
alerting the operator that there is a serious problem that needs to be
addressed.

Fixes #40442.

Release note (general change): nodes that have been terminated as the
result of a failed consistency check now refuse to restart, making it
more likely that the operator notices that there is a persistent issue
in a timely manner.

pkg/base/store_spec.go

@@ -13,7 +13,9 @@ package base
 import (
 	"bytes"
 	"fmt"
+	"io/ioutil"
 	"net"
+	"os"
 	"path/filepath"
 	"regexp"
 	"sort"
@@ -357,6 +359,51 @@ func (ssl StoreSpecList) String() string {
 	return buffer.String()
 }
 
+// AuxiliaryDir is the path of the auxiliary dir relative to an engine.Engine's
+// root directory. It must not be changed without a proper migration.
+const AuxiliaryDir = "auxiliary"
+
+// PreventedStartupFile is the filename (relative to 'dir') used for files that
+// can block server startup.
+func PreventedStartupFile(dir string) string {
+	return filepath.Join(dir, "_CRITICAL_ALERT.txt")
+}
+
+// PreventedStartupMessage attempts to read the PreventedStartupFile for each
+// store directory and returns their concatenated contents. These files
+// typically request operator intervention after a corruption event by
+// preventing the affected node(s) from starting back up.
+func (ssl StoreSpecList) GetPreventedStartupMessage() (string, error) {
+	var buf strings.Builder
+	for _, ss := range ssl.Specs {
+		path := ss.PreventedStartupFile()
+		if path == "" {
+			continue
+		}
+		b, err := ioutil.ReadFile(path)
+		if err != nil {
+			if !os.IsNotExist(err) {
+				return "", err
+			}
+			continue
+		}
+		fmt.Fprintf(&buf, "From %s:\n\n", path)
+		_, _ = buf.Write(b)
+		fmt.Fprintln(&buf)
+	}
+	return buf.String(), nil
+}
+
+// PreventedStartupFile returns the path to a file which, if it exists, should
+// prevent the server from starting up. Returns an empty string for in-memory
+// engines.
+func (ss StoreSpec) PreventedStartupFile() string {
+	if ss.InMemory {
+		return ""
+	}
+	return PreventedStartupFile(filepath.Join(ss.Path, AuxiliaryDir))
+}
+
 // Type returns the underlying type in string form. This is part of pflag's
 // value interface.
 func (ssl *StoreSpecList) Type() string {

pkg/base/store_spec_test.go

@@ -12,13 +12,17 @@ package base_test
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"reflect"
 	"testing"
 
 	"github.com/cockroachdb/cockroach/pkg/base"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/testutils"
 	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
+	"github.com/stretchr/testify/require"
 )
 
 // TestNewStoreSpec verifies that the --store arguments are correctly parsed
@@ -217,3 +221,37 @@ func TestJoinListType(t *testing.T) {
 		})
 	}
 }
+
+func TestStoreSpecListPreventedStartupMessage(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+
+	dir, cleanup := testutils.TempDir(t)
+	defer cleanup()
+
+	boomStoreDir := filepath.Join(dir, "boom")
+	boomAuxDir := filepath.Join(boomStoreDir, base.AuxiliaryDir)
+	okStoreDir := filepath.Join(dir, "ok")
+	okAuxDir := filepath.Join(okStoreDir, base.AuxiliaryDir)
+
+	for _, sd := range []string{boomAuxDir, okAuxDir} {
+		require.NoError(t, os.MkdirAll(sd, 0755))
+	}
+
+	ssl := base.StoreSpecList{
+		Specs: []base.StoreSpec{
+			{Path: "foo", InMemory: true},
+			{Path: okStoreDir},
+			{Path: boomStoreDir},
+		},
+	}
+
+	msg, err := ssl.GetPreventedStartupMessage()
+	require.NoError(t, err)
+	require.Empty(t, msg)
+
+	require.NoError(t, ioutil.WriteFile(ssl.Specs[2].PreventedStartupFile(), []byte("boom"), 0644))
+
+	msg, err = ssl.GetPreventedStartupMessage()
+	require.NoError(t, err)
+	require.Contains(t, msg, "boom")
+}

pkg/cli/start.go

@@ -444,6 +444,12 @@ func runStart(cmd *cobra.Command, args []string, disableReplication bool) error
 		return err
 	}
 
+	if s, err := serverCfg.Stores.GetPreventedStartupMessage(); err != nil {
+		return err
+	} else if s != "" {
+		log.Fatal(context.Background(), s)
+	}
+
 	// Set up the signal handlers. This also ensures that any of these
 	// signals received beyond this point do not interrupt the startup
 	// sequence until the point signals are checked below.

pkg/storage/consistency_queue_test.go

@@ -14,6 +14,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"io/ioutil"
 	"math/rand"
 	"path/filepath"
 	"testing"
@@ -35,6 +36,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/syncutil"
 	"github.com/cockroachdb/cockroach/pkg/util/uuid"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 // TestConsistencyQueueRequiresLive verifies the queue will not
@@ -356,6 +358,11 @@ func TestCheckConsistencyInconsistent(t *testing.T) {
 	assert.Equal(t, roachpb.CheckConsistencyResponse_RANGE_INCONSISTENT, resp.Result[0].Status)
 	assert.Contains(t, resp.Result[0].Detail, `[minority]`)
 	assert.Contains(t, resp.Result[0].Detail, `stats`)
+
+	// A death rattle should have been written on s2 (store index 1).
+	b, err := ioutil.ReadFile(base.PreventedStartupFile(mtc.stores[1].Engine().GetAuxiliaryDir()))
+	require.NoError(t, err)
+	require.NotEmpty(t, b)
 }
 
 // TestConsistencyQueueRecomputeStats is an end-to-end test of the mechanism CockroachDB

pkg/storage/engine/pebble.go

@@ -278,7 +278,7 @@ func NewPebble(ctx context.Context, cfg PebbleConfig) (*Pebble, error) {
 			return nil, err
 		}
 	} else {
-		auxDir = cfg.Opts.FS.PathJoin(cfg.Dir, "auxiliary")
+		auxDir = cfg.Opts.FS.PathJoin(cfg.Dir, base.AuxiliaryDir)
 		if err := cfg.Opts.FS.MkdirAll(auxDir, 0755); err != nil {
 			return nil, err
 		}

pkg/storage/engine/rocksdb.go

@@ -528,7 +528,7 @@ func NewRocksDB(cfg RocksDBConfig, cache RocksDBCache) (*RocksDB, error) {
 		cache: cache.ref(),
 	}
 
-	if err := r.setAuxiliaryDir(filepath.Join(cfg.Dir, "auxiliary")); err != nil {
+	if err := r.setAuxiliaryDir(filepath.Join(cfg.Dir, base.AuxiliaryDir)); err != nil {
 		return nil, err
 	}
 

pkg/storage/replica_proposal.go

@@ -13,12 +13,14 @@ package storage
 import (
 	"context"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
 	"time"
 	"unsafe"
 
+	"github.com/cockroachdb/cockroach/pkg/base"
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
 	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
@@ -256,14 +258,34 @@ func (r *Replica) computeChecksumPostApply(ctx context.Context, cc storagepb.Com
 			// holder and thus won't be printed to the logs. Since we're already
 			// in a goroutine that's about to end, simply sleep for a few seconds
 			// and then terminate.
+			auxDir := r.store.engine.GetAuxiliaryDir()
+			_ = os.MkdirAll(auxDir, 0755)
+			path := base.PreventedStartupFile(auxDir)
+
+			preventStartupMsg := fmt.Sprintf(`ATTENTION:
+
+this node is terminating because a replica inconsistency was detected between %s
+and its other replicas. Please check your cluster-wide log files for more
+information and contact the CockroachDB support team. It is not necessarily safe
+to replace this node; cluster data may still be at risk of corruption.
+
+A file preventing this node from restarting was placed at:
+%s
+
+A checkpoints directory to aid (expert) debugging should be present in:
+%s
+`, r, path, auxDir)
+			log.Infof(ctx, "TBG %s", path)
+
+			if err := ioutil.WriteFile(path, []byte(preventStartupMsg), 0644); err != nil {
+				log.Warning(ctx, err)
+			}
+
 			if p := r.store.cfg.TestingKnobs.ConsistencyTestingKnobs.OnBadChecksumFatal; p != nil {
 				p(*r.store.Ident)
 			} else {
 				time.Sleep(10 * time.Second)
-				log.Fatalf(r.AnnotateCtx(context.Background()),
-					"this node is terminating because a replica inconsistency was detected "+
-						"between %s and its other replicas. Please check your cluster-wide log files for "+
-						"more information and contact the CockroachDB support team.", r)
+				log.Fatalf(r.AnnotateCtx(context.Background()), preventStartupMsg)
 			}
 		}