Refactor to call non-voting servers read replicas (#9191)

Co-authored-by: Kit Patella <kit@jepsen.io>

.changelog/9191.txt

@@ -0,0 +1,18 @@
+```release-note:deprecation
+cli: **(Enterprise only)** The `-non-voting-server` flag is deprecated in favor of the new `-read-replica` flag. The `-non-voting-server` flag is still present along side the new flag but it will be removed in a future release. 
+```
+```release-note:improvement
+cli: **(Enterprise only)** A new `-read-replica` flag can now be used to enable running a server as a read only replica. Previously this was enabled with the now deprecated `-non-voting-server` flag.
+```
+```release-note:deprecation
+config: **(Enterprise only)** The `non_voting_server` configuration setting is deprecated in favor of the new `read_replica` setting. The `non_voting_server` configuration setting is still present but will be removed in a future release.
+```
+```release-note:improvement
+config: **(Enterprise only)** A new `read_replica` configuration setting can now be used to enable running a server as a read only replica. Previously this was enabled with the now deprecated `non_voting_server` setting.
+```
+```release-note:deprecation
+server: **(Enterprise only)** Addition of the `nonvoter` tag to the service registration made for read replicas is deprecated in favor of the new tag name of `read_replica`. Both are present in the registration but the `nonvoter` tag will be completely removed in a future release.
+```
+```release-note:deprecation
+gossip: **(Enterprise only)** Read replicas now advertise themselves by setting the `read_replica` tag. The old `nonvoter` tag is still present but is deprecated and will be removed in a future release.
+``` 

agent/agent.go

@@ -1110,8 +1110,8 @@ func newConsulConfig(runtimeCfg *config.RuntimeConfig, logger hclog.Logger) (*co
 	if runtimeCfg.SessionTTLMin != 0 {
 		cfg.SessionTTLMin = runtimeCfg.SessionTTLMin
 	}
-	if runtimeCfg.NonVotingServer {
-		cfg.NonVoter = runtimeCfg.NonVotingServer
+	if runtimeCfg.ReadReplica {
+		cfg.ReadReplica = runtimeCfg.ReadReplica
 	}
 
 	// These are fully specified in the agent defaults, so we can simply

agent/config/builder.go

@@ -1034,7 +1034,7 @@ func (b *Builder) Build() (rt RuntimeConfig, err error) {
 		NodeID:                      types.NodeID(b.stringVal(c.NodeID)),
 		NodeMeta:                    c.NodeMeta,
 		NodeName:                    b.nodeName(c.NodeName),
-		NonVotingServer:             b.boolVal(c.NonVotingServer),
+		ReadReplica:                 b.boolVal(c.ReadReplica),
 		PidFile:                     b.stringVal(c.PidFile),
 		PrimaryDatacenter:           primaryDatacenter,
 		PrimaryGateways:             b.expandAllOptionalAddrs("primary_gateways", c.PrimaryGateways),

agent/config/builder_oss.go

@@ -13,6 +13,9 @@ var (
 		"non_voting_server": func(c *Config) {
 			// to maintain existing compatibility we don't nullify the value
 		},
+		"read_replica": func(c *Config) {
+			// to maintain existing compatibility we don't nullify the value
+		},
 		"segment": func(c *Config) {
 			// to maintain existing compatibility we don't nullify the value
 		},

agent/config/builder_oss_test.go

@@ -24,11 +24,18 @@ func TestBuilder_validateEnterpriseConfigKeys(t *testing.T) {
 	cases := map[string]testCase{
 		"non_voting_server": {
 			config: Config{
-				NonVotingServer: &boolVal,
+				ReadReplica: &boolVal,
 			},
 			keys:    []string{"non_voting_server"},
 			badKeys: []string{"non_voting_server"},
 		},
+		"read_replica": {
+			config: Config{
+				ReadReplica: &boolVal,
+			},
+			keys:    []string{"read_replica"},
+			badKeys: []string{"read_replica"},
+		},
 		"segment": {
 			config: Config{
 				SegmentName: &stringVal,
@@ -118,11 +125,11 @@ func TestBuilder_validateEnterpriseConfigKeys(t *testing.T) {
 		},
 		"multi": {
 			config: Config{
-				NonVotingServer: &boolVal,
-				SegmentName:     &stringVal,
+				ReadReplica: &boolVal,
+				SegmentName: &stringVal,
 			},
-			keys:    []string{"non_voting_server", "segment", "acl.tokens.agent_master"},
-			badKeys: []string{"non_voting_server", "segment"},
+			keys:    []string{"non_voting_server", "read_replica", "segment", "acl.tokens.agent_master"},
+			badKeys: []string{"non_voting_server", "read_replica", "segment"},
 		},
 	}
 

agent/config/config.go

@@ -289,7 +289,7 @@ type Config struct {
 	// Enterprise Only
 	Audit *Audit `json:"audit,omitempty" hcl:"audit" mapstructure:"audit"`
 	// Enterprise Only
-	NonVotingServer *bool `json:"non_voting_server,omitempty" hcl:"non_voting_server" mapstructure:"non_voting_server"`
+	ReadReplica *bool `json:"read_replica,omitempty" hcl:"read_replica" mapstructure:"read_replica" alias:"non_voting_server"`
 	// Enterprise Only
 	SegmentName *string `json:"segment,omitempty" hcl:"segment" mapstructure:"segment"`
 	// Enterprise Only

agent/config/flags.go

@@ -89,7 +89,8 @@ func AddFlags(fs *flag.FlagSet, f *BuilderOpts) {
 	add(&f.Config.NodeName, "node", "Name of this node. Must be unique in the cluster.")
 	add(&f.Config.NodeID, "node-id", "A unique ID for this node across space and time. Defaults to a randomly-generated ID that persists in the data-dir.")
 	add(&f.Config.NodeMeta, "node-meta", "An arbitrary metadata key/value pair for this node, of the format `key:value`. Can be specified multiple times.")
-	add(&f.Config.NonVotingServer, "non-voting-server", "(Enterprise-only) This flag is used to make the server not participate in the Raft quorum, and have it only receive the data replication stream. This can be used to add read scalability to a cluster in cases where a high volume of reads to servers are needed.")
+	add(&f.Config.ReadReplica, "non-voting-server", "(Enterprise-only) DEPRECATED: -read-replica should be used instead")
+	add(&f.Config.ReadReplica, "read-replica", "(Enterprise-only) This flag is used to make the server not participate in the Raft quorum, and have it only receive the data replication stream. This can be used to add read scalability to a cluster in cases where a high volume of reads to servers are needed.")
 	add(&f.Config.PidFile, "pid-file", "Path to file to store agent PID.")
 	add(&f.Config.RPCProtocol, "protocol", "Sets the protocol version. Defaults to latest.")
 	add(&f.Config.RaftProtocol, "raft-protocol", "Sets the Raft protocol version. Defaults to latest.")

agent/config/runtime.go

@@ -845,12 +845,12 @@ type RuntimeConfig struct {
 	// flag: -node-meta "key:value" -node-meta "key:value" ...
 	NodeMeta map[string]string
 
-	// NonVotingServer is whether this server will act as a non-voting member
+	// ReadReplica is whether this server will act as a non-voting member
 	// of the cluster to help provide read scalability. (Enterprise-only)
 	//
 	// hcl: non_voting_server = (true|false)
 	// flag: -non-voting-server
-	NonVotingServer bool
+	ReadReplica bool
 
 	// PidFile is the file to store our PID in.
 	//

agent/config/runtime_oss_test.go

@@ -12,12 +12,16 @@ var entTokenConfigSanitize = `"EnterpriseConfig": {},`
 
 func entFullRuntimeConfig(rt *RuntimeConfig) {}
 
-var enterpriseNonVotingServerWarnings []string = []string{enterpriseConfigKeyError{key: "non_voting_server"}.Error()}
+var enterpriseReadReplicaWarnings []string = []string{enterpriseConfigKeyError{key: "read_replica"}.Error()}
 
 var enterpriseConfigKeyWarnings []string
 
 func init() {
 	for k := range enterpriseConfigMap {
+		if k == "non_voting_server" {
+			// this is an alias for "read_replica" so we shouldn't see it in warnings
+			continue
+		}
 		enterpriseConfigKeyWarnings = append(enterpriseConfigKeyWarnings, enterpriseConfigKeyError{key: k}.Error())
 	}
 }

agent/config/runtime_test.go

@@ -610,10 +610,10 @@ func TestBuilder_BuildAndValidate_ConfigFlagsAndEdgecases(t *testing.T) {
 				`-data-dir=` + dataDir,
 			},
 			patch: func(rt *RuntimeConfig) {
-				rt.NonVotingServer = true
+				rt.ReadReplica = true
 				rt.DataDir = dataDir
 			},
-			warns: enterpriseNonVotingServerWarnings,
+			warns: enterpriseReadReplicaWarnings,
 		},
 		{
 			desc: "-pid-file",
@@ -5315,6 +5315,7 @@ func TestFullConfig(t *testing.T) {
 			"raft_snapshot_threshold": 16384,
 			"raft_snapshot_interval": "30s",
 			"raft_trailing_logs": 83749,
+			"read_replica": true,
 			"reconnect_timeout": "23739s",
 			"reconnect_timeout_wan": "26694s",
 			"recursors": [ "63.38.39.58", "92.49.18.18" ],
@@ -6004,6 +6005,7 @@ func TestFullConfig(t *testing.T) {
 			raft_snapshot_threshold = 16384
 			raft_snapshot_interval = "30s"
 			raft_trailing_logs = 83749
+			read_replica = true
 			reconnect_timeout = "23739s"
 			reconnect_timeout_wan = "26694s"
 			recursors = [ "63.38.39.58", "92.49.18.18" ]
@@ -6749,7 +6751,7 @@ func TestFullConfig(t *testing.T) {
 		NodeID:                  types.NodeID("AsUIlw99"),
 		NodeMeta:                map[string]string{"5mgGQMBk": "mJLtVMSG", "A7ynFMJB": "0Nx6RGab"},
 		NodeName:                "otlLxGaI",
-		NonVotingServer:         true,
+		ReadReplica:             true,
 		PidFile:                 "43xN80Km",
 		PrimaryDatacenter:       "ejtmd43d",
 		PrimaryGateways:         []string{"aej8eeZo", "roh2KahS"},
@@ -7684,13 +7686,13 @@ func TestSanitize(t *testing.T) {
 		"NodeID": "",
 		"NodeMeta": {},
 		"NodeName": "",
-		"NonVotingServer": false,
 		"PidFile": "",
 		"PrimaryDatacenter": "",
 		"PrimaryGateways": [
 			"pmgw_foo=bar pmgw_key=baz pmgw_secret=boom pmgw_bang=bar"
 		],
 		"PrimaryGatewaysInterval": "0s",
+		"ReadReplica": false,
 		"RPCAdvertiseAddr": "",
 		"RPCBindAddr": "",
 		"RPCHandshakeTimeout": "0s",

agent/consul/config.go

@@ -110,9 +110,9 @@ type Config struct {
 	// RaftConfig is the configuration used for Raft in the local DC
 	RaftConfig *raft.Config
 
-	// (Enterprise-only) NonVoter is used to prevent this server from being added
+	// (Enterprise-only) ReadReplica is used to prevent this server from being added
 	// as a voting member of the Raft cluster.
-	NonVoter bool
+	ReadReplica bool
 
 	// NotifyListen is called after the RPC listener has been configured.
 	// RPCAdvertise will be set to the listener address if it hasn't been

agent/consul/leader.go

@@ -1230,7 +1230,9 @@ func (s *Server) handleAliveMember(member serf.Member) error {
 				Warning: 1,
 			},
 			Meta: map[string]string{
+				// DEPRECATED - remove nonvoter in favor of read_replica in a future version of consul
 				"non_voter":             strconv.FormatBool(member.Tags["nonvoter"] == "1"),
+				"read_replica":          strconv.FormatBool(member.Tags["read_replica"] == "1"),
 				"raft_version":          strconv.Itoa(parts.RaftVersion),
 				"serf_protocol_current": strconv.FormatUint(uint64(member.ProtocolCur), 10),
 				"serf_protocol_min":     strconv.FormatUint(uint64(member.ProtocolMin), 10),

agent/consul/leader_test.go

@@ -334,7 +334,9 @@ func TestLeader_CheckServersMeta(t *testing.T) {
 	versionToExpect := "19.7.9"
 
 	retry.Run(t, func(r *retry.R) {
+		// DEPRECATED - remove nonvoter tag in favor of read_replica in a future version of consul
 		member.Tags["nonvoter"] = "1"
+		member.Tags["read_replica"] = "1"
 		member.Tags["build"] = versionToExpect
 		err := s1.handleAliveMember(member)
 		if err != nil {
@@ -347,9 +349,13 @@ func TestLeader_CheckServersMeta(t *testing.T) {
 		if service == nil {
 			r.Fatal("client not registered")
 		}
+		// DEPRECATED - remove non_voter in favor of read_replica in a future version of consul
 		if service.Meta["non_voter"] != "true" {
 			r.Fatalf("Expected to be non_voter == true, was: %s", service.Meta["non_voter"])
 		}
+		if service.Meta["read_replica"] != "true" {
+			r.Fatalf("Expected to be read_replica == true, was: %s", service.Meta["non_voter"])
+		}
 		newVersion := service.Meta["version"]
 		if newVersion != versionToExpect {
 			r.Fatalf("Expected version to be updated to %s, was %s", versionToExpect, newVersion)

agent/consul/server_serf.go

@@ -61,8 +61,11 @@ func (s *Server) setupSerf(conf *serf.Config, ch chan serf.Event, path string, w
 	if s.config.BootstrapExpect != 0 {
 		conf.Tags["expect"] = fmt.Sprintf("%d", s.config.BootstrapExpect)
 	}
-	if s.config.NonVoter {
+	if s.config.ReadReplica {
+		// DEPRECATED - This tag should be removed when we no longer want to support
+		// upgrades from 1.8.x and below
 		conf.Tags["nonvoter"] = "1"
+		conf.Tags["read_replica"] = "1"
 	}
 	if s.config.UseTLS {
 		conf.Tags["use_tls"] = "1"
@@ -351,7 +354,7 @@ func (s *Server) maybeBootstrap() {
 			s.logger.Error("Member has bootstrap mode. Expect disabled.", "member", member)
 			return
 		}
-		if !p.NonVoter {
+		if !p.ReadReplica {
 			voters++
 		}
 		servers = append(servers, *p)
@@ -410,7 +413,7 @@ func (s *Server) maybeBootstrap() {
 		id := raft.ServerID(server.ID)
 
 		suffrage := raft.Voter
-		if server.NonVoter {
+		if server.ReadReplica {
 			suffrage = raft.Nonvoter
 		}
 		peer := raft.Server{

agent/consul/server_test.go

@@ -240,7 +240,7 @@ func testServerDCExpectNonVoter(t *testing.T, dc string, expect int) (string, *S
 		c.Datacenter = dc
 		c.Bootstrap = false
 		c.BootstrapExpect = expect
-		c.NonVoter = true
+		c.ReadReplica = true
 	})
 }
 

agent/metadata/server.go

@@ -40,7 +40,7 @@ type Server struct {
 	RaftVersion  int
 	Addr         net.Addr
 	Status       serf.MemberStatus
-	NonVoter     bool
+	ReadReplica  bool
 	ACLs         structs.ACLMode
 	FeatureFlags map[string]int
 
@@ -160,7 +160,10 @@ func IsConsulServer(m serf.Member) (bool, *Server) {
 	}
 
 	// Check if the server is a non voter
+	// DEPRECATED - remove looking for the nonvoter tag eventually once we don't have to support
+	// read replicas running v1.8.x and below.
 	_, nonVoter := m.Tags["nonvoter"]
+	_, readReplica := m.Tags["read_replica"]
 
 	addr := &net.TCPAddr{IP: m.Addr, Port: port}
 
@@ -182,7 +185,8 @@ func IsConsulServer(m serf.Member) (bool, *Server) {
 		RaftVersion:  raftVsn,
 		Status:       m.Status,
 		UseTLS:       useTLS,
-		NonVoter:     nonVoter,
+		// DEPRECATED - remove nonVoter check once support for that tag is removed
+		ReadReplica:  nonVoter || readReplica,
 		ACLs:         acls,
 		FeatureFlags: featureFlags,
 	}

agent/metadata/server_test.go

@@ -66,7 +66,7 @@ func TestIsConsulServer(t *testing.T) {
 			"expect":        "3",
 			"raft_vsn":      "3",
 			"use_tls":       "1",
-			"nonvoter":      "1",
+			"read_replica":  "1",
 		},
 		Status: serf.StatusLeft,
 	}
@@ -101,7 +101,7 @@ func TestIsConsulServer(t *testing.T) {
 	if !parts.UseTLS {
 		t.Fatalf("bad: %v", parts.UseTLS)
 	}
-	if !parts.NonVoter {
+	if !parts.ReadReplica {
 		t.Fatalf("unexpected voter")
 	}
 	m.Tags["bootstrap"] = "1"
@@ -130,10 +130,16 @@ func TestIsConsulServer(t *testing.T) {
 		t.Fatalf("unexpected bootstrap")
 	}
 
-	delete(m.Tags, "nonvoter")
+	delete(m.Tags, "read_replica")
 	ok, parts = metadata.IsConsulServer(m)
-	if !ok || parts.NonVoter {
-		t.Fatalf("unexpected nonvoter")
+	if !ok || parts.ReadReplica {
+		t.Fatalf("unexpected read replica")
+	}
+
+	m.Tags["nonvoter"] = "1"
+	ok, parts = metadata.IsConsulServer(m)
+	if !ok || !parts.ReadReplica {
+		t.Fatalf("expected read replica")
 	}
 
 	delete(m.Tags, "role")

agent/structs/structs_filtering_test.go

@@ -11,12 +11,47 @@ import (
 
 	"github.com/hashicorp/consul/api"
 	bexpr "github.com/hashicorp/go-bexpr"
+	"github.com/mitchellh/pointerstructure"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
 var dumpFieldConfig = flag.Bool("dump-field-config", false, "generate field config dump file")
 
+func TestPointerStructure(t *testing.T) {
+	csn := CheckServiceNode{
+		Node: &Node{
+			ID:      "f18f3a10-2153-40ae-af7d-68db0e856498",
+			Node:    "node1",
+			Address: "198.18.0.1",
+		},
+		Service: &NodeService{
+			ID:      "test",
+			Service: "test",
+			Port:    1234,
+			TaggedAddresses: map[string]ServiceAddress{
+				"wan": {
+					Address: "1.1.1.1",
+					Port:    443,
+				},
+			},
+		},
+	}
+
+	ptr := pointerstructure.Pointer{
+		Parts: []string{
+			"Service",
+			"TaggedAddresses",
+			"wan",
+			"Address",
+		},
+	}
+
+	val, err := ptr.Get(csn)
+	require.NoError(t, err)
+	require.Equal(t, "1.1.1.1", val)
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // NOTE: The tests within this file are designed to validate that the fields

api/agent.go

@@ -158,6 +158,15 @@ const (
 	// configured to use TLS. Any other value indicates that it was not setup in
 	// that manner.
 	MemberTagValueUseTLS = "1"
+
+	// MemberTagKeyReadReplica is the key used to indicate that the member is a read
+	// replica server (will remain a Raft non-voter).
+	// Read Replicas are a Consul Enterprise feature.
+	MemberTagKeyReadReplica = "read_replica"
+	// MemberTagValueReadReplica is the value of the MemberTagKeyReadReplica key when
+	// the member is in fact a read-replica. Any other value indicates that it is not.
+	// Read Replicas are a Consul Enterprise feature.
+	MemberTagValueReadReplica = "1"
 )
 
 type MemberACLMode string

website/pages/docs/agent/options.mdx

@@ -479,7 +479,10 @@ The options below are all specified on the command-line.
   This overrides the default server RPC port 8300. This is available in Consul 1.2.2
   and later.
 
-- `-non-voting-server` ((#\_non_voting_server)) <EnterpriseAlert inline /> - This
+- `-non-voting-server` ((#\_non_voting_server)) <EnterpriseAlert inline /> - **This field 
+  is deprecated in Consul 1.9.1. See the [`-read-replica`](#_read_replica) flag instead.**
+
+- `-read-replica` ((#\_read_replica)) <EnterpriseAlert inline /> - This
   flag is used to make the server not participate in the Raft quorum, and have it
   only receive the data replication stream. This can be used to add read scalability
   to a cluster in cases where a high volume of reads to servers are needed.
@@ -1852,7 +1855,9 @@ Valid time units are 'ns', 'us' (or 'µs'), 'ms', 's', 'm', 'h'."
 
 - `server` Equivalent to the [`-server` command-line flag](#_server).
 
-- `non_voting_server` - Equivalent to the [`-non-voting-server` command-line flag](#_non_voting_server).
+- `non_voting_server` - **This field is deprecated in Consul 1.9.1. See the [`read_replica`](#read_replica) field instead.**
+
+- `read_replica` - Equivalent to the [`-read-replica` command-line flag](#_read_replica).
 
 - `server_name` When provided, this overrides the [`node_name`](#_node)
   for the TLS certificate. It can be used to ensure that the certificate name matches

website/pages/docs/enterprise/read-scale.mdx

@@ -4,12 +4,10 @@ page_title: Consul Enterprise Enhanced Read Scalability
 sidebar_title: Enhanced Read Scalability
 description: >-
   Consul Enterprise supports increased read scalability without impacting write
-  latency by introducing
-
-  non-voting servers.
+  latency by introducing read replicas.
 ---
 
-# Enhanced Read Scalability with Non-Voting Servers
+# Enhanced Read Scalability with Read Replicas
 
 <EnterpriseAlert>
   This feature requires{' '}
@@ -18,10 +16,10 @@ description: >-
 </EnterpriseAlert>
 
 Consul Enterprise provides the ability to scale clustered Consul servers
-to include voting and non-voting servers. Non-voting servers still receive data from the cluster replication,
+to include voting servers and read replicas. Read replicas still receive data from the cluster replication,
 however, they do not take part in quorum election operations. Expanding your Consul cluster in this way can scale
 reads without impacting write latency.
 
 For more details, review the [Consul server configuration](/docs/agent/options)
-documentation and the [-non-voting-server](/docs/agent/options#_non_voting_server)
+documentation and the [-read-replica](/docs/agent/options#_read_replica)
 configuration flag.