Change keys of the discovery flags such that they conform to the convention

changelog/22.0/22.0.0/summary.md

@@ -8,6 +8,7 @@
   - **[RPC Changes](#rpc-changes)**
   - **[Prefer not promoting a replica that is currently taking a backup](#reparents-prefer-not-backing-up)**
   - **[VTOrc Config File Changes](#vtorc-config-file-changes)**
+  - **[VTGate Config File Changes](#vtgate-config-file-changes)**
   - **[Support for More Efficient JSON Replication](#efficient-json-replication)**
 - **[Minor Changes](#minor-changes)**
   - **[VTTablet Flags](#flags-vttablet)**
@@ -60,6 +61,19 @@ The following fields can be dynamically changed -
 
 To upgrade to the newer version of the configuration file, first switch to using the flags in your current deployment before upgrading. Then you can switch to using the configuration file in the newer release.
 
+### <a id="vtgate-config-file-changes"/>VTGate Config File Changes</a>
+
+The Viper configuration keys for the following flags has been changed to match their flag names. Previously they had a discovery prefix instead of it being part of the name. 
+
+| Flag Name                                        | Old Configuration Key                            | New Configuration Key                            |
+|--------------------------------------------------|--------------------------------------------------|--------------------------------------------------|
+| `discovery_low_replication_lag`                  | `discovery.low_replication_lag`                  | `discovery_low_replication_lag`                  |
+| `discovery_high_replication_lag_minimum_serving` | `discovery.high_replication_lag_minimum_serving` | `discovery_high_replication_lag_minimum_serving` |
+| `discovery_min_number_serving_vttablets`         | `discovery.min_number_serving_vttablets`         | `discovery_min_number_serving_vttablets`         |
+| `discovery_legacy_replication_lag_algorithm`     | `discovery.legacy_replication_lag_algorithm`     | `discovery_legacy_replication_lag_algorithm`     |
+
+To upgrade to the newer version of the configuration keys, first switch to using the flags in your current deployment before upgrading. Then you can switch to using the new configuration keys in the newer release.
+
 ### <a id="efficient-json-replication"/>Support for More Efficient JSON Replication</a>
 
 In [#7345](https://github.com/vitessio/vitess/pull/17345) we added support for [`--binlog-row-value-options=PARTIAL_JSON`](https://dev.mysql.com/doc/refman/en/replication-options-binary-log.html#sysvar_binlog_row_value_options). You can read more about [this feature added to MySQL 8.0 here](https://dev.mysql.com/blog-archive/efficient-json-replication-in-mysql-8-0/).

go/test/endtoend/cluster/vtgate_process.go

@@ -70,7 +70,11 @@ type VtgateProcess struct {
 }
 
 type VTGateConfiguration struct {
-	TransactionMode string `json:"transaction_mode,omitempty"`
+	TransactionMode                   string `json:"transaction_mode,omitempty"`
+	DiscoveryLowReplicationLag        string `json:"discovery_low_replication_lag,omitempty"`
+	DiscoveryHighReplicationLag       string `json:"discovery_high_replication_lag,omitempty"`
+	DiscoveryMinServingVttablets      string `json:"discovery_min_number_serving_vttablets,omitempty"`
+	DiscoveryLegacyReplicationLagAlgo string `json:"discovery_legacy_replication_lag_algorithm"`
 }
 
 // ToJSONString will marshal this configuration as JSON

go/test/endtoend/vtgate/misc_test.go

@@ -814,6 +814,81 @@ func TestDDLTargeted(t *testing.T) {
 	utils.AssertMatches(t, conn, `select id from ddl_targeted`, `[[INT64(1)]]`)
 }
 
+// TestDynamicConfig tests the dynamic configurations.
+func TestDynamicConfig(t *testing.T) {
+	t.Run("DiscoveryLowReplicationLag", func(t *testing.T) {
+		// Test initial config value
+		err := clusterInstance.VtgateProcess.WaitForConfig(`"discovery_low_replication_lag":30000000000`)
+		require.NoError(t, err)
+		defer func() {
+			// Restore default back.
+			clusterInstance.VtgateProcess.Config.DiscoveryLowReplicationLag = "30s"
+			err = clusterInstance.VtgateProcess.RewriteConfiguration()
+			require.NoError(t, err)
+		}()
+		clusterInstance.VtgateProcess.Config.DiscoveryLowReplicationLag = "15s"
+		err = clusterInstance.VtgateProcess.RewriteConfiguration()
+		require.NoError(t, err)
+		// Test final config value.
+		err = clusterInstance.VtgateProcess.WaitForConfig(`"discovery_low_replication_lag":"15s"`)
+		require.NoError(t, err)
+	})
+
+	t.Run("DiscoveryHighReplicationLag", func(t *testing.T) {
+		// Test initial config value
+		err := clusterInstance.VtgateProcess.WaitForConfig(`"discovery_high_replication_lag":7200000000000`)
+		require.NoError(t, err)
+		defer func() {
+			// Restore default back.
+			clusterInstance.VtgateProcess.Config.DiscoveryHighReplicationLag = "2h"
+			err = clusterInstance.VtgateProcess.RewriteConfiguration()
+			require.NoError(t, err)
+		}()
+		clusterInstance.VtgateProcess.Config.DiscoveryHighReplicationLag = "1h"
+		err = clusterInstance.VtgateProcess.RewriteConfiguration()
+		require.NoError(t, err)
+		// Test final config value.
+		err = clusterInstance.VtgateProcess.WaitForConfig(`"discovery_high_replication_lag":"1h"`)
+		require.NoError(t, err)
+	})
+
+	t.Run("DiscoveryMinServingVttablets", func(t *testing.T) {
+		// Test initial config value
+		err := clusterInstance.VtgateProcess.WaitForConfig(`"discovery_min_number_serving_vttablets":2`)
+		require.NoError(t, err)
+		defer func() {
+			// Restore default back.
+			clusterInstance.VtgateProcess.Config.DiscoveryMinServingVttablets = "2"
+			err = clusterInstance.VtgateProcess.RewriteConfiguration()
+			require.NoError(t, err)
+		}()
+		clusterInstance.VtgateProcess.Config.DiscoveryMinServingVttablets = "1"
+		err = clusterInstance.VtgateProcess.RewriteConfiguration()
+		require.NoError(t, err)
+		// Test final config value.
+		err = clusterInstance.VtgateProcess.WaitForConfig(`"discovery_min_number_serving_vttablets":"1"`)
+		require.NoError(t, err)
+	})
+
+	t.Run("DiscoveryLegacyReplicationLagAlgo", func(t *testing.T) {
+		// Test initial config value
+		err := clusterInstance.VtgateProcess.WaitForConfig(`"discovery_legacy_replication_lag_algorithm":""`)
+		require.NoError(t, err)
+		defer func() {
+			// Restore default back.
+			clusterInstance.VtgateProcess.Config.DiscoveryLegacyReplicationLagAlgo = "true"
+			err = clusterInstance.VtgateProcess.RewriteConfiguration()
+			require.NoError(t, err)
+		}()
+		clusterInstance.VtgateProcess.Config.DiscoveryLegacyReplicationLagAlgo = "false"
+		err = clusterInstance.VtgateProcess.RewriteConfiguration()
+		require.NoError(t, err)
+		// Test final config value.
+		err = clusterInstance.VtgateProcess.WaitForConfig(`"discovery_legacy_replication_lag_algorithm":"false"`)
+		require.NoError(t, err)
+	})
+}
+
 func TestLookupErrorMetric(t *testing.T) {
 	conn, closer := start(t)
 	defer closer()

go/vt/discovery/replicationlag.go

@@ -28,34 +28,33 @@ import (
 )
 
 var (
-	configKey = viperutil.KeyPrefixFunc("discovery")
 	// lowReplicationLag defines the duration that replication lag is low enough that the VTTablet is considered healthy.
 	lowReplicationLag = viperutil.Configure(
-		configKey("low_replication_lag"),
+		"discovery_low_replication_lag",
 		viperutil.Options[time.Duration]{
 			FlagName: "discovery_low_replication_lag",
 			Default:  30 * time.Second,
 			Dynamic:  true,
 		},
 	)
 	highReplicationLagMinServing = viperutil.Configure(
-		configKey("high_replication_lag"),
+		"discovery_high_replication_lag",
 		viperutil.Options[time.Duration]{
 			FlagName: "discovery_high_replication_lag_minimum_serving",
 			Default:  2 * time.Hour,
 			Dynamic:  true,
 		},
 	)
 	minNumTablets = viperutil.Configure(
-		configKey("min_number_serving_vttablets"),
+		"discovery_min_number_serving_vttablets",
 		viperutil.Options[int]{
 			FlagName: "min_number_serving_vttablets",
 			Default:  2,
 			Dynamic:  true,
 		},
 	)
 	legacyReplicationLagAlgorithm = viperutil.Configure(
-		configKey("legacy_replication_lag_algorithm"),
+		"discovery_legacy_replication_lag_algorithm",
 		viperutil.Options[bool]{
 			FlagName: "legacy_replication_lag_algorithm",
 			Default:  true,