vtgate: support filtering tablets by tablet-tags

go/flags/endtoend/vtcombo.txt

@@ -337,6 +337,7 @@ Flags:
       --stream_health_buffer_size uint                                   max streaming health entries to buffer per streaming health client (default 20)
       --table-refresh-interval int                                       interval in milliseconds to refresh tables in status page with refreshRequired class
       --table_gc_lifecycle string                                        States for a DROP TABLE garbage collection cycle. Default is 'hold,purge,evac,drop', use any subset ('drop' implicitly always included) (default "hold,purge,evac,drop")
+      --tablet-filter-tags StringMap                                     Specifies a comma-separated list of tablet tags (as key:value pairs) to filter the tablets to watch.
       --tablet_dir string                                                The directory within the vtdataroot to store vttablet/mysql files. Defaults to being generated by the tablet uid.
       --tablet_filters strings                                           Specifies a comma-separated list of 'keyspace|shard_name or keyrange' values to filter the tablets to watch.
       --tablet_health_keep_alive duration                                close streaming tablet health connection if there are no requests for this long (default 5m0s)

go/flags/endtoend/vtgate.txt

@@ -195,6 +195,7 @@ Flags:
       --stderrthreshold severityFlag                                     logs at or above this threshold go to stderr (default 1)
       --stream_buffer_size int                                           the number of bytes sent from vtgate for each stream call. It's recommended to keep this value in sync with vttablet's query-server-config-stream-buffer-size. (default 32768)
       --table-refresh-interval int                                       interval in milliseconds to refresh tables in status page with refreshRequired class
+      --tablet-filter-tags StringMap                                     Specifies a comma-separated list of tablet tags (as key:value pairs) to filter the tablets to watch.
       --tablet_filters strings                                           Specifies a comma-separated list of 'keyspace|shard_name or keyrange' values to filter the tablets to watch.
       --tablet_grpc_ca string                                            the server ca to use to validate servers when connecting
       --tablet_grpc_cert string                                          the cert to use to connect

go/vt/discovery/healthcheck.go

@@ -48,6 +48,7 @@ import (
 	"github.com/spf13/pflag"
 	"golang.org/x/sync/semaphore"
 
+	"vitess.io/vitess/go/flagutil"
 	"vitess.io/vitess/go/netutil"
 	"vitess.io/vitess/go/stats"
 	"vitess.io/vitess/go/vt/log"
@@ -82,6 +83,9 @@ var (
 	// tabletFilters are the keyspace|shard or keyrange filters to apply to the full set of tablets.
 	tabletFilters []string
 
+	// tabletFilterTags are the tablet tag filters (as key:value pairs) to apply to the full set of tablets.
+	tabletFilterTags flagutil.StringMapValue
+
 	// refreshInterval is the interval at which healthcheck refreshes its list of tablets from topo.
 	refreshInterval = 1 * time.Minute
 
@@ -164,6 +168,7 @@ func init() {
 
 func registerDiscoveryFlags(fs *pflag.FlagSet) {
 	fs.StringSliceVar(&tabletFilters, "tablet_filters", []string{}, "Specifies a comma-separated list of 'keyspace|shard_name or keyrange' values to filter the tablets to watch.")
+	fs.Var(&tabletFilterTags, "tablet-filter-tags", "Specifies a comma-separated list of tablet tags (as key:value pairs) to filter the tablets to watch.")
 	fs.Var((*topoproto.TabletTypeListFlag)(&AllowedTabletTypes), "allowed_tablet_types", "Specifies the tablet types this vtgate is allowed to route queries to. Should be provided as a comma-separated set of tablet types.")
 	fs.StringSliceVar(&KeyspacesToWatch, "keyspaces_to_watch", []string{}, "Specifies which keyspaces this vtgate should have access to while routing queries or accessing the vschema.")
 }
@@ -337,13 +342,13 @@ func NewHealthCheck(ctx context.Context, retryDelay, healthCheckTimeout time.Dur
 		loadTabletsTrigger: make(chan struct{}),
 	}
 	var topoWatchers []*TopologyWatcher
-	var filter TabletFilter
 	cells := strings.Split(cellsToWatch, ",")
 	if cellsToWatch == "" {
 		cells = append(cells, localCell)
 	}
 
 	for _, c := range cells {
+		var filters TabletFilters
 		log.Infof("Setting up healthcheck for cell: %v", c)
 		if c == "" {
 			continue
@@ -357,11 +362,14 @@ func NewHealthCheck(ctx context.Context, retryDelay, healthCheckTimeout time.Dur
 			if err != nil {
 				log.Exitf("Cannot parse tablet_filters parameter: %v", err)
 			}
-			filter = fbs
+			filters = append(filters, fbs)
 		} else if len(KeyspacesToWatch) > 0 {
-			filter = NewFilterByKeyspace(KeyspacesToWatch)
+			filters = append(filters, NewFilterByKeyspace(KeyspacesToWatch))
+		}
+		if len(tabletFilterTags) > 0 {
+			filters = append(filters, NewFilterByTabletTags(tabletFilterTags))
 		}
-		topoWatchers = append(topoWatchers, NewTopologyWatcher(ctx, topoServer, hc, filter, c, refreshInterval, refreshKnownTablets, topo.DefaultConcurrency))
+		topoWatchers = append(topoWatchers, NewTopologyWatcher(ctx, topoServer, hc, filters, c, refreshInterval, refreshKnownTablets, topo.DefaultConcurrency))
 	}
 
 	hc.topoWatchers = topoWatchers

go/vt/discovery/topology_watcher.go

@@ -274,6 +274,19 @@ type TabletFilter interface {
 	IsIncluded(tablet *topodata.Tablet) bool
 }
 
+// TabletFilters contains filters for tablets.
+type TabletFilters []TabletFilter
+
+// IsIncluded returns true if a tablet passes all filters.
+func (tf TabletFilters) IsIncluded(tablet *topodata.Tablet) bool {
+	for _, filter := range tf {
+		if !filter.IsIncluded(tablet) {
+			return false
+		}
+	}
+	return true
+}
+
 // FilterByShard is a filter that filters tablets by
 // keyspace/shard.
 type FilterByShard struct {
@@ -375,3 +388,32 @@ func (fbk *FilterByKeyspace) IsIncluded(tablet *topodata.Tablet) bool {
 	_, exist := fbk.keyspaces[tablet.Keyspace]
 	return exist
 }
+
+// FilterByTabletTags is a filter that filters tablets by tablet tag key/values.
+type FilterByTabletTags struct {
+	tags map[string]string
+}
+
+// NewFilterByTabletTags creates a new FilterByTabletTags. All tablets that match
+// all tablet tags will be forwarded to the TopologyWatcher's consumer.
+func NewFilterByTabletTags(tabletTags map[string]string) *FilterByTabletTags {
+	return &FilterByTabletTags{
+		tags: tabletTags,
+	}
+}
+
+// IsIncluded returns true if the tablet's tags match what we expect.
+func (fbtg *FilterByTabletTags) IsIncluded(tablet *topodata.Tablet) bool {
+	if fbtg.tags == nil {
+		return true
+	}
+	if tablet.Tags == nil {
+		return false
+	}
+	for key, val := range fbtg.tags {
+		if tabletVal, found := tablet.Tags[key]; !found || tabletVal != val {
+			return false
+		}
+	}
+	return true
+}

go/vt/discovery/topology_watcher_test.go

@@ -393,7 +393,7 @@ func TestFilterByKeyspace(t *testing.T) {
 	ctx := utils.LeakCheckContext(t)
 
 	hc := NewFakeHealthCheck(nil)
-	f := NewFilterByKeyspace(testKeyspacesToWatch)
+	f := TabletFilters{NewFilterByKeyspace(testKeyspacesToWatch)}
 	ts := memorytopo.NewServer(ctx, testCell)
 	defer ts.Close()
 	tw := NewTopologyWatcher(context.Background(), ts, hc, f, testCell, 10*time.Minute, true, 5)
@@ -476,7 +476,7 @@ func TestFilterByKeyspaceSkipsIgnoredTablets(t *testing.T) {
 	defer fhc.Close()
 	topologyWatcherOperations.ZeroAll()
 	counts := topologyWatcherOperations.Counts()
-	f := NewFilterByKeyspace(testKeyspacesToWatch)
+	f := TabletFilters{NewFilterByKeyspace(testKeyspacesToWatch)}
 	tw := NewTopologyWatcher(context.Background(), ts, fhc, f, "aa", 10*time.Minute, false /*refreshKnownTablets*/, 5)
 
 	counts = checkOpCounts(t, counts, map[string]int64{})
@@ -578,6 +578,33 @@ func TestFilterByKeyspaceSkipsIgnoredTablets(t *testing.T) {
 	tw.Stop()
 }
 
+func TestNewFilterByTabletTags(t *testing.T) {
+	// no required tags == true
+	filter := NewFilterByTabletTags(nil)
+	assert.True(t, filter.IsIncluded(&topodatapb.Tablet{}))
+
+	tags := map[string]string{
+		"instance_type": "i3.xlarge",
+		"some_key":      "some_value",
+	}
+	filter = NewFilterByTabletTags(tags)
+
+	assert.False(t, filter.IsIncluded(&topodatapb.Tablet{
+		Tags: nil,
+	}))
+	assert.False(t, filter.IsIncluded(&topodatapb.Tablet{
+		Tags: map[string]string{},
+	}))
+	assert.False(t, filter.IsIncluded(&topodatapb.Tablet{
+		Tags: map[string]string{
+			"instance_type": "i3.xlarge",
+		},
+	}))
+	assert.True(t, filter.IsIncluded(&topodatapb.Tablet{
+		Tags: tags,
+	}))
+}
+
 func TestGetTabletErrorDoesNotRemoveFromHealthcheck(t *testing.T) {
 	ctx := utils.LeakCheckContext(t)