Merge pull request #67 from fly-apps/runtime-zombie-analysis-2

Evaluate quorum at runtime

Author: davissp14

cmd/event_handler/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"log"
@@ -10,6 +11,7 @@ import (
 	"time"
 
 	"github.com/fly-apps/postgres-flex/internal/flypg"
+	"github.com/jackc/pgx/v5"
 )
 
 const eventLogFile = "/data/event.log"
@@ -26,6 +28,8 @@ func main() {
 	details := flag.String("details", "", "details")
 	flag.Parse()
 
+	ctx := context.Background()
+
 	logFile, err := os.OpenFile(eventLogFile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0644)
 	if err != nil {
 		fmt.Printf("failed to open event log: %s", err)
@@ -91,6 +95,38 @@ func main() {
 			os.Exit(1)
 		}
 
+	case "child_node_disconnect", "child_node_reconnect", "child_node_new_connect":
+		node, err := flypg.NewNode()
+		if err != nil {
+			log.Printf("failed to initialize node: %s", err)
+			os.Exit(1)
+		}
+
+		conn, err := node.RepMgr.NewLocalConnection(ctx)
+		if err != nil {
+			log.Printf("failed to open local connection: %s", err)
+			os.Exit(1)
+		}
+		defer conn.Close(ctx)
+
+		member, err := node.RepMgr.Member(ctx, conn)
+		if err != nil {
+			log.Printf("failed to resolve member: %s", err)
+			os.Exit(1)
+		}
+
+		if member.Role != flypg.PrimaryRoleName {
+			// We should never get here.
+			log.Println("skipping since we are not the primary")
+			os.Exit(0)
+		}
+
+		if err := evaluateClusterState(ctx, conn, node); err != nil {
+			log.Printf("failed to evaluate cluster state: %s", err)
+			os.Exit(0)
+		}
+
+		os.Exit(0)
 	default:
 		// noop
 	}
@@ -118,3 +154,50 @@ func reconfigurePGBouncer(id int) error {
 
 	return nil
 }
+
+func evaluateClusterState(ctx context.Context, conn *pgx.Conn, node *flypg.Node) error {
+	standbys, err := node.RepMgr.StandbyMembers(ctx, conn)
+	if err != nil {
+		if !errors.Is(err, pgx.ErrNoRows) {
+			return fmt.Errorf("failed to query standbys")
+		}
+	}
+
+	sample, err := flypg.TakeDNASample(ctx, node, standbys)
+	if err != nil {
+		return fmt.Errorf("failed to evaluate cluster data: %s", err)
+	}
+
+	log.Println(flypg.DNASampleString(sample))
+
+	primary, err := flypg.ZombieDiagnosis(sample)
+	if errors.Is(err, flypg.ErrZombieDiagnosisUndecided) || errors.Is(err, flypg.ErrZombieDiscovered) {
+		// Quarantine primary
+		if err := flypg.Quarantine(ctx, conn, node, primary); err != nil {
+			return fmt.Errorf("failed to quarantine failed primary: %s", err)
+		}
+
+		return fmt.Errorf("primary has been quarantined: %s", err)
+	} else if err != nil {
+		return fmt.Errorf("failed to run zombie diagnosis: %s", err)
+	}
+
+	// Clear zombie lock if it exists
+	if flypg.ZombieLockExists() {
+		log.Println("Clearing zombie lock and enabling read/write")
+		if err := flypg.RemoveZombieLock(); err != nil {
+			return fmt.Errorf("failed to remove zombie lock: %s", err)
+		}
+
+		log.Println("Broadcasting readonly state change")
+		if err := flypg.BroadcastReadonlyChange(ctx, node, false); err != nil {
+			log.Printf("errors while disabling readonly: %s", err)
+		}
+	}
+
+	if err := node.PGBouncer.ConfigurePrimary(ctx, primary, true); err != nil {
+		return fmt.Errorf("failed to reconfigure pgbouncer primary %s", err)
+	}
+
+	return nil
+}

internal/flypg/node.go

@@ -145,7 +145,7 @@ func (n *Node) Init(ctx context.Context) error {
 
 	if ZombieLockExists() {
 		fmt.Println("Zombie lock detected!")
-		primaryStr, err := readZombieLock()
+		primaryStr, err := ReadZombieLock()
 		if err != nil {
 			return fmt.Errorf("failed to read zombie lock: %s", primaryStr)
 		}
@@ -172,7 +172,7 @@ func (n *Node) Init(ctx context.Context) error {
 			// Confirm that our rejoin target still identifies itself as the primary.
 			if primary.Hostname != ip.String() {
 				// Clear the zombie.lock file so we can attempt to re-resolve the correct primary.
-				if err := removeZombieLock(); err != nil {
+				if err := RemoveZombieLock(); err != nil {
 					return fmt.Errorf("failed to remove zombie lock: %s", err)
 				}
 
@@ -191,7 +191,7 @@ func (n *Node) Init(ctx context.Context) error {
 
 			// TODO - Wait for target cluster to register self as a standby.
 
-			if err := removeZombieLock(); err != nil {
+			if err := RemoveZombieLock(); err != nil {
 				return fmt.Errorf("failed to remove zombie lock: %s", err)
 			}
 
@@ -348,45 +348,25 @@ func (n *Node) PostInit(ctx context.Context) error {
 				return fmt.Errorf("failed to resolve cluster metrics: %s", err)
 			}
 
-			printDNASample(sample)
+			fmt.Println(DNASampleString(sample))
 
 			// Evaluate whether we are a zombie or not.
 			primary, err := ZombieDiagnosis(sample)
 			if errors.Is(err, ErrZombieDiagnosisUndecided) {
 				fmt.Println("Unable to confirm that we are the true primary!")
 
-				fmt.Println("Writing zombie.lock file.")
-				if err := writeZombieLock(""); err != nil {
-					return fmt.Errorf("failed to set zombie lock: %s", err)
+				if err := Quarantine(ctx, conn, n, primary); err != nil {
+					return fmt.Errorf("failed to quarantine failed primary: %s", err)
 				}
 
-				fmt.Println("Turning all user-created databases readonly.")
-				if err := BroadcastReadonlyChange(ctx, n, true); err != nil {
-					return fmt.Errorf("failed to set read-only: %s", err)
-				}
-
-				// TODO - Add link to docs
-				fmt.Println("Please refer to following documentation for more information: <insert-doc-link-here>.")
-
 			} else if errors.Is(err, ErrZombieDiscovered) {
-				fmt.Println("Zombie primary discovered!")
 				fmt.Printf("The majority of registered members agree that '%s' is the real primary.\n", primary)
 
-				fmt.Printf("Reconfiguring PGBouncer to point to '%s'\n", primary)
-				if err := n.PGBouncer.ConfigurePrimary(ctx, primary, true); err != nil {
-					return fmt.Errorf("failed to reconfigure pgbouncer: %s", err)
-				}
-
-				fmt.Println("Writing zombie.lock file")
-				if err := writeZombieLock(primary); err != nil {
-					return fmt.Errorf("failed to set zombie lock: %s", err)
-				}
-
-				fmt.Println("Turning user-created databases read-only")
-				if err := BroadcastReadonlyChange(ctx, n, true); err != nil {
-					return fmt.Errorf("failed to set read-only: %s", err)
+				if err := Quarantine(ctx, conn, n, primary); err != nil {
+					return fmt.Errorf("failed to quarantine failed primary: %s", err)
 				}
-
+				// Issue panic to force a process restart so we can attempt to rejoin
+				// the the cluster we've diverged from.
 				panic(err)
 			} else if err != nil {
 				return fmt.Errorf("failed to run zombie diagnosis: %s", err)

internal/flypg/pgbouncer.go

@@ -62,7 +62,7 @@ func (p *PGBouncer) ConfigurePrimary(ctx context.Context, primary string, reload
 	if reload {
 		err = p.reloadConfig(ctx)
 		if err != nil {
-			fmt.Printf("failed to reconfigure pgbouncer primary %s\n", err)
+			return fmt.Errorf("failed to reconfigure pgbouncer primary: %s", err)
 		}
 	}
 	return nil

internal/flypg/readonly.go

@@ -124,7 +124,7 @@ func changeReadOnlyState(ctx context.Context, n *Node, enable bool) error {
 
 	databases, err := admin.ListDatabases(ctx, conn)
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to list database: %s", err)
 	}
 
 	var dbNames []string

internal/flypg/repmgr.go

@@ -123,7 +123,7 @@ func (r *RepMgr) setDefaults() {
 		"promote_command":              fmt.Sprintf("'repmgr standby promote -f %s --log-to-file'", r.ConfigPath),
 		"follow_command":               fmt.Sprintf("'repmgr standby follow -f %s --log-to-file --upstream-node-id=%%n'", r.ConfigPath),
 		"event_notification_command":   fmt.Sprintf("'/usr/local/bin/event_handler -node-id %%n -event %%e -success %%s -details \"%%d\" -new-node-id \\'%%p\\''"),
-		"event_notifications":          "'repmgrd_failover_promote,standby_promote,standby_follow'",
+		"event_notifications":          "'repmgrd_failover_promote,standby_promote,standby_follow,child_node_disconnect,child_node_reconnect,child_node_new_connect'",
 		"location":                     r.Region,
 		"primary_visibility_consensus": true,
 		"failover_validation_command":  fmt.Sprintf("'/usr/local/bin/failover_validation -visible-nodes %%v -total-nodes %%t'"),

internal/flypg/restore.go

@@ -210,7 +210,7 @@ func clearLocks() error {
 		}
 	}
 
-	if err := removeZombieLock(); err != nil {
+	if err := RemoveZombieLock(); err != nil {
 		if !os.IsNotExist(err) {
 			return fmt.Errorf("failed to remove zombie lock pre-restore: %s", err)
 		}

internal/flypg/zombie.go

@@ -5,6 +5,8 @@ import (
 	"errors"
 	"fmt"
 	"os"
+
+	"github.com/jackc/pgx/v5"
 )
 
 var (
@@ -35,15 +37,15 @@ func writeZombieLock(hostname string) error {
 	return nil
 }
 
-func removeZombieLock() error {
+func RemoveZombieLock() error {
 	if err := os.Remove("/data/zombie.lock"); err != nil {
 		return err
 	}
 
 	return nil
 }
 
-func readZombieLock() (string, error) {
+func ReadZombieLock() (string, error) {
 	body, err := os.ReadFile("/data/zombie.lock")
 	if err != nil {
 		return "", err
@@ -142,8 +144,27 @@ func ZombieDiagnosis(s *DNASample) (string, error) {
 	return "", ErrZombieDiagnosisUndecided
 }
 
-func printDNASample(s *DNASample) {
-	fmt.Printf("Registered members: %d, Active member(s): %d, Inactive member(s): %d, Conflicts detected: %d\n",
+func Quarantine(ctx context.Context, conn *pgx.Conn, n *Node, primary string) error {
+	if primary != "" {
+		if err := n.PGBouncer.ConfigurePrimary(ctx, primary, true); err != nil {
+			return fmt.Errorf("failed to reconfigure pgbouncer: %s", err)
+		}
+	}
+
+	fmt.Println("Writing zombie.lock file.")
+	if err := writeZombieLock(""); err != nil {
+		return fmt.Errorf("failed to set zombie lock: %s", err)
+	}
+
+	if err := BroadcastReadonlyChange(ctx, n, true); err != nil {
+		return fmt.Errorf("failed to set read-only: %s", err)
+	}
+
+	return nil
+}
+
+func DNASampleString(s *DNASample) string {
+	return fmt.Sprintf("Registered members: %d, Active member(s): %d, Inactive member(s): %d, Conflicts detected: %d",
 		s.totalMembers,
 		s.totalActive,
 		s.totalInactive,