Add more e2e tests

Signed-off-by: Mohamed Hamza <mhamza15@github.com>

Author: mhamza15

go/test/endtoend/vtgate/sessionbalancer/main_test.go

@@ -18,71 +18,226 @@ package sessionbalancer
 
 import (
 	"context"
+	_ "embed"
+	"fmt"
+	"slices"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 
 	"vitess.io/vitess/go/mysql"
+	"vitess.io/vitess/go/test/endtoend/cluster"
 )
 
+const (
+	cell     = "test_misc"
+	keyspace = "uks"
+)
+
+//go:embed uschema.sql
+var uschemaSQL string
+
+func createCluster(t *testing.T, replicaCount int) (*cluster.LocalProcessCluster, *mysql.ConnParams) {
+	t.Helper()
+
+	// Create a new clusterInstance
+	clusterInstance := cluster.NewCluster(cell, "localhost")
+
+	// Start topo server
+	err := clusterInstance.StartTopo()
+	require.NoError(t, err, "Failed to start topo server")
+
+	// Enable session balancer in vtgate
+	clusterInstance.VtGateExtraArgs = append(clusterInstance.VtGateExtraArgs,
+		"--enable-balancer",
+		"--balancer-vtgate-cells", clusterInstance.Cell,
+		"--balancer-type", "session")
+
+	ks := cluster.Keyspace{
+		Name:      keyspace,
+		SchemaSQL: uschemaSQL,
+	}
+	err = clusterInstance.StartUnshardedKeyspace(ks, replicaCount, false)
+	require.NoError(t, err, "Failed to start keyspace")
+
+	err = clusterInstance.StartVtgate()
+	require.NoError(t, err, "Failed to start vtgate")
+
+	vtParams := clusterInstance.GetVTParams(keyspace)
+
+	return clusterInstance, &vtParams
+}
+
 // TestSessionBalancer validates that the session balancer consistently routes
 // queries for the same session to the same tablet.
 func TestSessionBalancer(t *testing.T) {
+	cluster, vtParams := createCluster(t, 2)
+	defer cluster.Teardown()
+
+	// Get connections that route to different tablets
+	conns, ids := connections(t, vtParams, "replica", 2)
+
+	for _, conn := range conns {
+		defer conn.Close()
+	}
+
+	// Validate that each connection consistently returns the same server ID
+	for range 20 {
+		for i, conn := range conns {
+			id := serverID(t, conn)
+			require.Equal(t, ids[i], id)
+		}
+	}
+}
+
+// TestSessionBalancerRemoveTablet validates that when a tablet is killed,
+// connections that were using that tablet get rerouted to remaining tablets.
+func TestSessionBalancerRemoveTablet(t *testing.T) {
+	cluster, vtParams := createCluster(t, 2)
+	defer cluster.Teardown()
+
 	// Get connections that route to different tablets
-	conn1, conn2, id1, id2 := connections(t)
+	conns, _ := connections(t, vtParams, "replica", 2)
+	conn1, conn2 := conns[0], conns[1]
 
 	defer conn1.Close()
 	defer conn2.Close()
 
-	// Validate that each connection consistently returns the same server ID
+	tablets := tablets(t, cluster, "replica")
+	require.NotNil(t, tablets)
+	require.Len(t, tablets, 2)
+
+	err := tablets[0].VttabletProcess.TearDown()
+	require.NoError(t, err)
+
+	time.Sleep(10 * time.Millisecond)
+
 	for range 20 {
 		newID1 := serverID(t, conn1)
-		require.Equal(t, id1, newID1)
-
 		newID2 := serverID(t, conn2)
-		require.Equal(t, id2, newID2)
 
-		require.NotEqual(t, newID2, newID1)
+		require.Equal(t, newID1, newID2)
+	}
+}
+
+// TestSessionBalancerAddTablet validates that when a new tablet is added,
+// new connections get routed to the new tablet.
+func TestSessionBalancerAddTablet(t *testing.T) {
+	cluster, vtParams := createCluster(t, 3)
+	defer cluster.Teardown()
+
+	// Get 3 connections that route to different tablets
+	conns, ids := connections(t, vtParams, "replica", 3)
+	for _, conn := range conns {
+		defer conn.Close()
+	}
+
+	tablets := tablets(t, cluster, "replica")
+	require.NotNil(t, tablets)
+	require.Len(t, tablets, 3)
+
+	// Start with only 2 tablets serving
+	tablet := tablets[2]
+	err := tablet.VttabletProcess.TearDown()
+	require.NoError(t, err)
+
+	time.Sleep(10 * time.Millisecond)
+
+	// Find the connection that moved
+	var conn *mysql.Conn
+	for i, c := range conns {
+		newID := serverID(t, c)
+		if newID != ids[i] {
+			conn = c
+			break
+		}
+	}
+
+	require.NotNil(t, conn, "One connection should've moved tablets")
+
+	// Start up the tablet again
+	err = tablet.RestartOnlyTablet()
+	require.NoError(t, err)
+
+	time.Sleep(10 * time.Millisecond)
+
+	// All connections should route to the same IDs again
+	for range 20 {
+		for i, conn := range conns {
+			id := ids[i]
+			newID := serverID(t, conn)
+			require.Equal(t, id, newID)
+		}
 	}
 }
 
-// connections returns two connections that should route to different servers.
-func connections(t *testing.T) (conn1, conn2 *mysql.Conn, id1, id2 string) {
+// connections returns the specified number of connections that should route to different tablets.
+func connections(t *testing.T, vtParams *mysql.ConnParams, tabletType string, numConnections int) ([]*mysql.Conn, []string) {
 	t.Helper()
 
-	// Keep creating connections until we find two that route to different server IDs
-	vtParams.DbName = uks + "@replica"
-	for {
-		conn1, err := mysql.Connect(context.Background(), &vtParams)
-		require.NoError(t, err)
+	vtParams.DbName = fmt.Sprintf("%s@%s", keyspace, tabletType)
+
+	conns := make([]*mysql.Conn, 0, numConnections)
+	ids := make([]string, 0, numConnections)
 
-		conn2, err = mysql.Connect(context.Background(), &vtParams)
+	// Keep creating connections until we have the required number with different server IDs
+	for range 20 {
+		conn, err := mysql.Connect(context.Background(), vtParams)
 		require.NoError(t, err)
 
-		id1 = serverID(t, conn1)
-		id2 = serverID(t, conn2)
+		id := serverID(t, conn)
+		newID := !slices.Contains(ids, id)
+
+		// If we found a new tablet, add it to the list of connections
+		if newID {
+			conns = append(conns, conn)
+			ids = append(ids, id)
+
+			if len(conns) == numConnections {
+				return conns, ids
+			}
 
-		// Break if we found connections with different server IDs
-		if id1 != id2 {
-			return conn1, conn2, id1, id2
+			continue
 		}
 
-		// If not, close the connections and try again
-		conn1.Close()
-		conn2.Close()
+		conn.Close()
 	}
+
+	t.Fatalf("could not create %d connections with different tablet connections", numConnections)
+	return nil, nil
 }
 
-// serverID runs a `SELECT @@server_id` on the given connection and returns the
-// server's ID.
+// serverID runs a `SELECT @@server_id` on the given connection and returns the server's ID.
 func serverID(t *testing.T, conn *mysql.Conn) string {
 	t.Helper()
 
-	result1, err := conn.ExecuteFetch("SELECT @@server_uuid", 1, false)
+	result1, err := conn.ExecuteFetch("SELECT @@server_id", 1, false)
 	require.NoError(t, err)
 
 	tablet1Bytes, err := result1.Rows[0][0].ToBytes()
 	require.NoError(t, err)
 
 	return string(tablet1Bytes)
 }
+
+func tablets(t *testing.T, clusterInstance *cluster.LocalProcessCluster, tabletType string) []*cluster.Vttablet {
+	t.Helper()
+
+	if len(clusterInstance.Keyspaces) == 0 {
+		return nil
+	}
+
+	if len(clusterInstance.Keyspaces[0].Shards) == 0 {
+		return nil
+	}
+
+	tablets := make([]*cluster.Vttablet, 0, 2)
+	for _, tablet := range clusterInstance.Keyspaces[0].Shards[0].Vttablets {
+		if tablet.Type == tabletType {
+			tablets = append(tablets, tablet)
+		}
+	}
+
+	return tablets
+}

go/test/endtoend/vtgate/sessionbalancer/session_test.go

@@ -2,8 +2,3 @@ CREATE TABLE t1 (
     id int PRIMARY KEY,
     name varchar(255)
 );
-
-CREATE TABLE t2 (
-    id int PRIMARY KEY,
-    value varchar(255)
-);