core: remove all traces of unused protocol version

Nomad inherited protocol version numbering configuration from Consul and
Serf, but unlike those projects Nomad has never used it. Nomad's
`protocol_version` has always been `1`.

While the code is effectively unused and therefore poses no runtime
risks to leave, I felt like removing it was best because:

1. Nomad's RPC subsystem has been able to evolve extensively without
   needing to increment the version number.
2. Nomad's HTTP API has evolved extensively without increment
   `API{Major,Minor}Version`. If we want to version the HTTP API in the
   future, I doubt this is the mechanism we would choose.
3. The presence of the `server.protocol_version` configuration
   parameter is confusing since `server.raft_protocol` *is* an important
   parameter for operators to consider. Even more confusing is that
   there is a distinct Serf protocol version which is included in `nomad
   server members` output under the heading `Protocol`. `raft_protocol`
   is the *only* protocol version relevant to Nomad developers and
   operators. The other protocol versions are either deadcode or have
   never changed (Serf).
4. If we were to need to version the RPC, HTTP API, or Serf protocols, I
   don't think these configuration parameters and variables are the best
   choice. If we come to that point we should choose a versioning scheme
   based on the use case and modern best practices -- not this 6+ year
   old dead code.

client/client.go

@@ -749,18 +749,6 @@ func (c *Client) secretNodeID() string {
 	return c.config.Node.SecretID
 }
 
-// RPCMajorVersion returns the structs.ApiMajorVersion supported by the
-// client.
-func (c *Client) RPCMajorVersion() int {
-	return structs.ApiMajorVersion
-}
-
-// RPCMinorVersion returns the structs.ApiMinorVersion supported by the
-// client.
-func (c *Client) RPCMinorVersion() int {
-	return structs.ApiMinorVersion
-}
-
 // Shutdown is used to tear down the client
 func (c *Client) Shutdown() error {
 	c.shutdownLock.Lock()
@@ -2773,7 +2761,7 @@ DISCOLOOP:
 				continue
 			}
 			var peers []string
-			if err := c.connPool.RPC(region, addr, c.RPCMajorVersion(), "Status.Peers", rpcargs, &peers); err != nil {
+			if err := c.connPool.RPC(region, addr, "Status.Peers", rpcargs, &peers); err != nil {
 				mErr.Errors = append(mErr.Errors, err)
 				continue
 			}

client/rpc.go

@@ -74,7 +74,7 @@ TRY:
 	}
 
 	// Make the request.
-	rpcErr := c.connPool.RPC(c.Region(), server.Addr, c.RPCMajorVersion(), method, args, reply)
+	rpcErr := c.connPool.RPC(c.Region(), server.Addr, method, args, reply)
 
 	if rpcErr == nil {
 		c.fireRpcRetryWatcher()
@@ -427,7 +427,7 @@ func resolveServer(s string) (net.Addr, error) {
 // a potential error.
 func (c *Client) Ping(srv net.Addr) error {
 	var reply struct{}
-	err := c.connPool.RPC(c.Region(), srv, c.RPCMajorVersion(), "Status.Ping", struct{}{}, &reply)
+	err := c.connPool.RPC(c.Region(), srv, "Status.Ping", struct{}{}, &reply)
 	return err
 }
 

command/agent/agent.go

@@ -191,9 +191,6 @@ func convertServerConfig(agentConfig *Config) (*nomad.Config, error) {
 	if agentConfig.Server.DataDir != "" {
 		conf.DataDir = agentConfig.Server.DataDir
 	}
-	if agentConfig.Server.ProtocolVersion != 0 {
-		conf.ProtocolVersion = uint8(agentConfig.Server.ProtocolVersion)
-	}
 	if agentConfig.Server.RaftProtocol != 0 {
 		conf.RaftConfig.ProtocolVersion = raft.ProtocolVersion(agentConfig.Server.RaftProtocol)
 	}

command/agent/command.go

@@ -413,6 +413,12 @@ func (c *Command) isValidConfig(config, cmdConfig *Config) bool {
 		}
 	}
 
+	// ProtocolVersion has never been used. Warn if it is set as someone
+	// has probably made a mistake.
+	if config.Server.ProtocolVersion != 0 {
+		c.agent.logger.Warn("Please remove deprecated protocol_version field from config.")
+	}
+
 	return true
 }
 

command/agent/config.go

@@ -385,6 +385,8 @@ type ServerConfig struct {
 
 	// ProtocolVersion is the protocol version to speak. This must be between
 	// ProtocolVersionMin and ProtocolVersionMax.
+	//
+	// Deprecated: This has never been used and will emit a warning if nonzero.
 	ProtocolVersion int `hcl:"protocol_version"`
 
 	// RaftProtocol is the Raft protocol version to speak. This must be from [1-3].

command/agent/testdata/basic.hcl

@@ -106,7 +106,6 @@ server {
   authoritative_region          = "foobar"
   bootstrap_expect              = 5
   data_dir                      = "/tmp/data"
-  protocol_version              = 3
   raft_protocol                 = 3
   num_schedulers                = 2
   enabled_schedulers            = ["test"]

command/agent/testdata/basic.json

@@ -277,7 +277,6 @@
       "node_gc_threshold": "12h",
       "non_voting_server": true,
       "num_schedulers": 2,
-      "protocol_version": 3,
       "raft_protocol": 3,
       "raft_multiplier": 4,
       "redundancy_zone": "foo",

helper/pool/pool.go

@@ -48,7 +48,6 @@ type Conn struct {
 	addr     net.Addr
 	session  *yamux.Session
 	lastUsed time.Time
-	version  int
 
 	pool *ConnPool
 
@@ -278,7 +277,7 @@ func (p *ConnPool) SetConnListener(l chan<- *Conn) {
 
 // Acquire is used to get a connection that is
 // pooled or to return a new connection
-func (p *ConnPool) acquire(region string, addr net.Addr, version int) (*Conn, error) {
+func (p *ConnPool) acquire(region string, addr net.Addr) (*Conn, error) {
 	// Check to see if there's a pooled connection available. This is up
 	// here since it should the vastly more common case than the rest
 	// of the code here.
@@ -305,7 +304,7 @@ func (p *ConnPool) acquire(region string, addr net.Addr, version int) (*Conn, er
 	// If we are the lead thread, make the new connection and then wake
 	// everybody else up to see if we got it.
 	if isLeadThread {
-		c, err := p.getNewConn(region, addr, version)
+		c, err := p.getNewConn(region, addr)
 		p.Lock()
 		delete(p.limiter, addr.String())
 		close(wait)
@@ -349,7 +348,7 @@ func (p *ConnPool) acquire(region string, addr net.Addr, version int) (*Conn, er
 }
 
 // getNewConn is used to return a new connection
-func (p *ConnPool) getNewConn(region string, addr net.Addr, version int) (*Conn, error) {
+func (p *ConnPool) getNewConn(region string, addr net.Addr) (*Conn, error) {
 	// Try to dial the conn
 	conn, err := net.DialTimeout("tcp", addr.String(), 10*time.Second)
 	if err != nil {
@@ -404,7 +403,6 @@ func (p *ConnPool) getNewConn(region string, addr net.Addr, version int) (*Conn,
 		session:  session,
 		clients:  list.New(),
 		lastUsed: time.Now(),
-		version:  version,
 		pool:     p,
 	}
 	return c, nil
@@ -429,12 +427,12 @@ func (p *ConnPool) clearConn(conn *Conn) {
 	}
 }
 
-// getClient is used to get a usable client for an address and protocol version
-func (p *ConnPool) getRPCClient(region string, addr net.Addr, version int) (*Conn, *StreamClient, error) {
+// getClient is used to get a usable client for an address
+func (p *ConnPool) getRPCClient(region string, addr net.Addr) (*Conn, *StreamClient, error) {
 	retries := 0
 START:
 	// Try to get a conn first
-	conn, err := p.acquire(region, addr, version)
+	conn, err := p.acquire(region, addr)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to get conn: %v", err)
 	}
@@ -457,8 +455,8 @@ START:
 
 // StreamingRPC is used to make an streaming RPC call.  Callers must
 // close the connection when done.
-func (p *ConnPool) StreamingRPC(region string, addr net.Addr, version int) (net.Conn, error) {
-	conn, err := p.acquire(region, addr, version)
+func (p *ConnPool) StreamingRPC(region string, addr net.Addr) (net.Conn, error) {
+	conn, err := p.acquire(region, addr)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get conn: %v", err)
 	}
@@ -477,9 +475,9 @@ func (p *ConnPool) StreamingRPC(region string, addr net.Addr, version int) (net.
 }
 
 // RPC is used to make an RPC call to a remote host
-func (p *ConnPool) RPC(region string, addr net.Addr, version int, method string, args interface{}, reply interface{}) error {
+func (p *ConnPool) RPC(region string, addr net.Addr, method string, args interface{}, reply interface{}) error {
 	// Get a usable client
-	conn, sc, err := p.getRPCClient(region, addr, version)
+	conn, sc, err := p.getRPCClient(region, addr)
 	if err != nil {
 		return fmt.Errorf("rpc error: %w", err)
 	}

nomad/client_rpc.go

@@ -188,8 +188,7 @@ func (s *Server) serverWithNodeConn(nodeID, region string) (*serverParts, error)
 
 		// Make the RPC
 		var resp structs.NodeConnQueryResponse
-		err := s.connPool.RPC(s.config.Region, server.Addr, server.MajorVersion,
-			"Status.HasNodeConn", &req, &resp)
+		err := s.connPool.RPC(s.config.Region, server.Addr, "Status.HasNodeConn", &req, &resp)
 		if err != nil {
 			multierror.Append(&rpcErr, fmt.Errorf("failed querying server %q: %v", server.Addr.String(), err))
 			continue

nomad/config.go

@@ -1,7 +1,6 @@
 package nomad
 
 import (
-	"fmt"
 	"io"
 	"net"
 	"os"
@@ -27,23 +26,6 @@ const (
 	DefaultSerfPort = 4648
 )
 
-// These are the protocol versions that Nomad can understand
-const (
-	ProtocolVersionMin uint8 = 1
-	ProtocolVersionMax       = 1
-)
-
-// ProtocolVersionMap is the mapping of Nomad protocol versions
-// to Serf protocol versions. We mask the Serf protocols using
-// our own protocol version.
-var protocolVersionMap map[uint8]uint8
-
-func init() {
-	protocolVersionMap = map[uint8]uint8{
-		1: 4,
-	}
-}
-
 func DefaultRPCAddr() *net.TCPAddr {
 	return &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 4647}
 }
@@ -93,10 +75,6 @@ type Config struct {
 	// Logger is the logger used by the server.
 	Logger log.InterceptLogger
 
-	// ProtocolVersion is the protocol version to speak. This must be between
-	// ProtocolVersionMin and ProtocolVersionMax.
-	ProtocolVersion uint8
-
 	// RPCAddr is the RPC address used by Nomad. This should be reachable
 	// by the other servers and clients
 	RPCAddr *net.TCPAddr
@@ -370,18 +348,6 @@ type Config struct {
 	DeploymentQueryRateLimit float64
 }
 
-// CheckVersion is used to check if the ProtocolVersion is valid
-func (c *Config) CheckVersion() error {
-	if c.ProtocolVersion < ProtocolVersionMin {
-		return fmt.Errorf("Protocol version '%d' too low. Must be in range: [%d, %d]",
-			c.ProtocolVersion, ProtocolVersionMin, ProtocolVersionMax)
-	} else if c.ProtocolVersion > ProtocolVersionMax {
-		return fmt.Errorf("Protocol version '%d' too high. Must be in range: [%d, %d]",
-			c.ProtocolVersion, ProtocolVersionMin, ProtocolVersionMax)
-	}
-	return nil
-}
-
 // DefaultConfig returns the default configuration. Only used as the basis for
 // merging agent or test parameters.
 func DefaultConfig() *Config {
@@ -396,7 +362,6 @@ func DefaultConfig() *Config {
 		Datacenter:                       DefaultDC,
 		NodeName:                         hostname,
 		NodeID:                           uuid.Generate(),
-		ProtocolVersion:                  ProtocolVersionMax,
 		RaftConfig:                       raft.DefaultConfig(),
 		RaftTimeout:                      10 * time.Second,
 		LogOutput:                        os.Stderr,

nomad/eval_broker.go

@@ -274,6 +274,8 @@ func (b *EvalBroker) enqueueWaiting(eval *structs.Evaluation) {
 }
 
 // enqueueLocked is used to enqueue with the lock held
+//
+// Are all evaluations we're enqueueing at this point pending? <---
 func (b *EvalBroker) enqueueLocked(eval *structs.Evaluation, queue string) {
 	// Do nothing if not enabled
 	if !b.enabled {

nomad/node_endpoint.go

@@ -267,8 +267,6 @@ func (n *Node) constructNodeServerInfoResponse(snap *state.StateSnapshot, reply
 		reply.Servers = append(reply.Servers,
 			&structs.NodeServerInfo{
 				RPCAdvertiseAddr: v.RPCAddr.String(),
-				RPCMajorVersion:  int32(v.MajorVersion),
-				RPCMinorVersion:  int32(v.MinorVersion),
 				Datacenter:       v.Datacenter,
 			})
 	}

nomad/rpc.go

@@ -612,7 +612,7 @@ func (r *rpcHandler) forwardLeader(server *serverParts, method string, args inte
 	if server == nil {
 		return structs.ErrNoLeader
 	}
-	return r.connPool.RPC(r.config.Region, server.Addr, server.MajorVersion, method, args, reply)
+	return r.connPool.RPC(r.config.Region, server.Addr, method, args, reply)
 }
 
 // forwardServer is used to forward an RPC call to a particular server
@@ -621,7 +621,7 @@ func (r *rpcHandler) forwardServer(server *serverParts, method string, args inte
 	if server == nil {
 		return errors.New("must be given a valid server address")
 	}
-	return r.connPool.RPC(r.config.Region, server.Addr, server.MajorVersion, method, args, reply)
+	return r.connPool.RPC(r.config.Region, server.Addr, method, args, reply)
 }
 
 func (r *rpcHandler) findRegionServer(region string) (*serverParts, error) {
@@ -648,7 +648,7 @@ func (r *rpcHandler) forwardRegion(region, method string, args interface{}, repl
 
 	// Forward to remote Nomad
 	metrics.IncrCounter([]string{"nomad", "rpc", "cross-region", region}, 1)
-	return r.connPool.RPC(region, server.Addr, server.MajorVersion, method, args, reply)
+	return r.connPool.RPC(region, server.Addr, method, args, reply)
 }
 
 func (r *rpcHandler) getServer(region, serverID string) (*serverParts, error) {
@@ -676,7 +676,7 @@ func (r *rpcHandler) getServer(region, serverID string) (*serverParts, error) {
 // initial handshake, returning the connection or an error. It is the callers
 // responsibility to close the connection if there is no returned error.
 func (r *rpcHandler) streamingRpc(server *serverParts, method string) (net.Conn, error) {
-	c, err := r.connPool.StreamingRPC(r.config.Region, server.Addr, server.MajorVersion)
+	c, err := r.connPool.StreamingRPC(r.config.Region, server.Addr)
 	if err != nil {
 		return nil, err
 	}

nomad/serf.go

@@ -164,7 +164,7 @@ func (s *Server) maybeBootstrap() {
 
 		// Retry with exponential backoff to get peer status from this server
 		for attempt := uint(0); attempt < maxPeerRetries; attempt++ {
-			if err := s.connPool.RPC(s.config.Region, server.Addr, server.MajorVersion,
+			if err := s.connPool.RPC(s.config.Region, server.Addr,
 				"Status.Peers", req, &peers); err != nil {
 				nextRetry := (1 << attempt) * peerRetryBase
 				s.logger.Error("failed to confirm peer status", "peer", server.Name, "error", err, "retry", nextRetry)