Add lease read option

server/config/config.go

@@ -31,6 +31,7 @@ import (
 	"go.etcd.io/etcd/pkg/v3/netutil"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v3discovery"
 	"go.etcd.io/etcd/server/v3/storage/datadir"
+	"go.etcd.io/raft/v3"
 )
 
 // ServerConfig holds the configuration of etcd as taken from the command line or discovery.
@@ -162,6 +163,8 @@ type ServerConfig struct {
 
 	ForceNewCluster bool
 
+	ReadOnlyOption raft.ReadOnlyOption `json:"read-only-option"`
+
 	// EnableLeaseCheckpoint enables leader to send regular checkpoints to other members to prevent reset of remaining TTL on leader change.
 	EnableLeaseCheckpoint bool
 	// LeaseCheckpointInterval time.Duration is the wait duration between lease checkpoints.

server/embed/config.go

@@ -360,6 +360,9 @@ type Config struct {
 	// ForceNewCluster starts a new cluster even if previously started; unsafe.
 	ForceNewCluster bool `json:"force-new-cluster"`
 
+	// LeaseRead enables to read value from leader lease without communicating with quorum.
+	LeaseRead bool `json:"lease-read"`
+
 	EnablePprof           bool   `json:"enable-pprof"`
 	Metrics               string `json:"metrics"`
 	ListenMetricsUrls     []url.URL
@@ -642,6 +645,7 @@ func (cfg *Config) AddFlags(fs *flag.FlagSet) {
 	fs.BoolVar(&cfg.StrictReconfigCheck, "strict-reconfig-check", cfg.StrictReconfigCheck, "Reject reconfiguration requests that would cause quorum loss.")
 
 	fs.BoolVar(&cfg.PreVote, "pre-vote", cfg.PreVote, "Enable to run an additional Raft election phase.")
+	fs.BoolVar(&cfg.LeaseRead, "lease-read", false, "Enable to read value from leader lease without communicating with quorum.")
 
 	// security
 	fs.StringVar(&cfg.ClientTLSInfo.CertFile, "cert-file", "", "Path to the client server TLS cert file.")

server/embed/etcd.go

@@ -50,6 +50,7 @@ import (
 	"go.etcd.io/etcd/server/v3/etcdserver/api/rafthttp"
 	"go.etcd.io/etcd/server/v3/storage"
 	"go.etcd.io/etcd/server/v3/verify"
+	"go.etcd.io/raft/v3"
 )
 
 const (
@@ -166,6 +167,11 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 
 	backendFreelistType := parseBackendFreelistType(cfg.BackendFreelistType)
 
+	readOnlyOption := raft.ReadOnlySafe
+	if cfg.LeaseRead {
+		readOnlyOption = raft.ReadOnlyLeaseBased
+	}
+
 	srvcfg := config.ServerConfig{
 		Name:                                     cfg.Name,
 		ClientURLs:                               cfg.AdvertiseClientUrls,
@@ -211,6 +217,7 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 		PreVote:                                  cfg.PreVote,
 		Logger:                                   cfg.logger,
 		ForceNewCluster:                          cfg.ForceNewCluster,
+		ReadOnlyOption:                           readOnlyOption,
 		EnableGRPCGateway:                        cfg.EnableGRPCGateway,
 		ExperimentalEnableDistributedTracing:     cfg.ExperimentalEnableDistributedTracing,
 		UnsafeNoFsync:                            cfg.UnsafeNoFsync,

server/etcdmain/help.go

@@ -162,6 +162,8 @@ Clustering:
     Auto compaction retention length. 0 means disable auto compaction.
   --auto-compaction-mode 'periodic'
     Interpret 'auto-compaction-retention' one of: periodic|revision. 'periodic' for duration based retention, defaulting to hours if no time unit is provided (e.g. '5m'). 'revision' for revision number based retention.
+  --lease-read 'false'
+    Enable to read value from leader lease without communicating with quorum.
   --v2-deprecation '` + string(cconfig.V2_DEPR_DEFAULT) + `'
     Phase of v2store deprecation. Allows to opt-in for higher compatibility mode.
     Supported values:

server/etcdserver/bootstrap.go

@@ -526,6 +526,7 @@ func raftConfig(cfg config.ServerConfig, id uint64, s *raft.MemoryStorage) *raft
 		CheckQuorum:     true,
 		PreVote:         cfg.PreVote,
 		Logger:          NewRaftLoggerZap(cfg.Logger.Named("raft")),
+		ReadOnlyOption:  cfg.ReadOnlyOption,
 	}
 }