Merge pull request #9482 from planetscale/ds-ignore-gateway-flag

Deprecate and ignore `gateway_implementation` flag to vtgate.

doc/releasenotes/13_0_0_summary.md

@@ -4,6 +4,9 @@
 
 ## Major Changes
 
+### vtgate -gateway_implementation flag is deprecated (and ignored)
+Support for `discoverygateway` is being dropped. `tabletgateway` is now the only supported implementation. Scripts using this flag should be updated to remove the flag as it will be deleted in the next release.
+
 ### vttablet -use_super_read_only flag now defaults to true
 The default value used to be false. What this means is that during a failover, we will set `super_read_only` on database flavors that support them (MySQL 5.7+ and Percona 5.7+).
 In addition, all Vitess-managed databases will be started with `super-read-only` in the cnf file.

go/vt/vtgate/gateway.go

@@ -35,10 +35,12 @@ import (
 // a query targeted to a keyspace/shard/tablet_type and send it off.
 
 var (
-	// GatewayImplementation allows you to choose which gateway to use for vtgate routing. Defaults to tabletgateway, other option is discoverygateway
-	GatewayImplementation = flag.String("gateway_implementation", "tabletgateway", "Allowed values: discoverygateway (deprecated), tabletgateway (default)")
-	bufferImplementation  = flag.String("buffer_implementation", "keyspace_events", "Allowed values: healthcheck (legacy implementation), keyspace_events (default)")
-	initialTabletTimeout  = flag.Duration("gateway_initial_tablet_timeout", 30*time.Second, "At startup, the gateway will wait up to that duration to get one tablet per keyspace/shard/tablettype")
+	_ = flag.String("gateway_implementation", "", "Deprecated. Only tabletgateway is now supported, discoverygateway is no longer available")
+	// We cannot reference tabletGatewayImplementation directly because it is const
+	defaultGatewayImplementation = tabletGatewayImplementation
+	GatewayImplementation        = &defaultGatewayImplementation
+	bufferImplementation         = flag.String("buffer_implementation", "keyspace_events", "Allowed values: healthcheck (legacy implementation), keyspace_events (default)")
+	initialTabletTimeout         = flag.Duration("gateway_initial_tablet_timeout", 30*time.Second, "At startup, the gateway will wait up to that duration to get one tablet per keyspace/shard/tablettype")
 	// RetryCount is the number of times a query will be retried on error
 	// Make this unexported after DiscoveryGateway is deprecated
 	RetryCount = flag.Int("retry-count", 2, "retry count")