client: don't use `Status` RPC for Consul discovery (#16490)

In #16217 we switched clients using Consul discovery to the `Status.Members`
endpoint for getting the list of servers so that we're using the correct
address. This endpoint has an authorization gate, so this fails if the anonymous
policy doesn't have `node:read`. We also can't check the `AuthToken` for the
request for the client secret, because the client hasn't yet registered so the
server doesn't have anything to compare against.

Instead of hitting the `Status.Peers` or `Status.Members` RPC endpoint, use the
Consul response directly. Update the `registerNode` method to handle the list of
servers we get back in the response; if we get a "no servers" or "no path to
region" response we'll kick off discovery again and retry immediately rather
than waiting 15s.

.changelog/16490.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+client: Fixed a bug where clients using Consul discovery to join the cluster would get permission denied errors
+```

client/client.go

@@ -1943,7 +1943,7 @@ func (c *Client) retryRegisterNode() {
 		}
 
 		retryIntv := registerRetryIntv
-		if err == noServersErr {
+		if err == noServersErr || structs.IsErrNoRegionPath(err) {
 			c.logger.Debug("registration waiting on servers")
 			c.triggerDiscovery()
 			retryIntv = noServerRetryIntv
@@ -1970,6 +1970,11 @@ func (c *Client) registerNode() error {
 		return err
 	}
 
+	err := c.handleNodeUpdateResponse(resp)
+	if err != nil {
+		return err
+	}
+
 	// Update the node status to ready after we register.
 	c.UpdateConfig(func(c *config.Config) {
 		c.Node.Status = structs.NodeStatusReady
@@ -1984,6 +1989,7 @@ func (c *Client) registerNode() error {
 	defer c.heartbeatLock.Unlock()
 	c.heartbeatStop.setLastOk(time.Now())
 	c.heartbeatTTL = resp.HeartbeatTTL
+
 	return nil
 }
 
@@ -2035,6 +2041,22 @@ func (c *Client) updateNodeStatus() error {
 		}
 	})
 
+	err := c.handleNodeUpdateResponse(resp)
+	if err != nil {
+		return fmt.Errorf("heartbeat response returned no valid servers")
+	}
+
+	// If there's no Leader in the response we may be talking to a partitioned
+	// server. Redo discovery to ensure our server list is up to date.
+	if resp.LeaderRPCAddr == "" {
+		c.triggerDiscovery()
+	}
+
+	c.EnterpriseClient.SetFeatures(resp.Features)
+	return nil
+}
+
+func (c *Client) handleNodeUpdateResponse(resp structs.NodeUpdateResponse) error {
 	// Update the number of nodes in the cluster so we can adjust our server
 	// rebalance rate.
 	c.servers.SetNumNodes(resp.NumNodes)
@@ -2051,20 +2073,9 @@ func (c *Client) updateNodeStatus() error {
 		nomadServers = append(nomadServers, e)
 	}
 	if len(nomadServers) == 0 {
-		return fmt.Errorf("heartbeat response returned no valid servers")
+		return noServersErr
 	}
 	c.servers.SetServers(nomadServers)
-
-	// Begin polling Consul if there is no Nomad leader.  We could be
-	// heartbeating to a Nomad server that is in the minority of a
-	// partition of the Nomad server quorum, but this Nomad Agent still
-	// has connectivity to the existing majority of Nomad Servers, but
-	// only if it queries Consul.
-	if resp.LeaderRPCAddr == "" {
-		c.triggerDiscovery()
-	}
-
-	c.EnterpriseClient.SetFeatures(resp.Features)
 	return nil
 }
 
@@ -2906,14 +2917,6 @@ func (c *Client) consulDiscoveryImpl() error {
 		dcs = dcs[0:helper.Min(len(dcs), datacenterQueryLimit)]
 	}
 
-	// Query for servers in this client's region only
-	region := c.Region()
-	rpcargs := structs.GenericRequest{
-		QueryOptions: structs.QueryOptions{
-			Region: region,
-		},
-	}
-
 	serviceName := c.GetConfig().ConsulConfig.ServerServiceName
 	var mErr multierror.Error
 	var nomadServers servers.Servers
@@ -2944,32 +2947,14 @@ DISCOLOOP:
 				continue
 			}
 
-			// Query the members from the region that Consul gave us, and
-			// extract the client-advertise RPC address from each member
-			var membersResp structs.ServerMembersResponse
-			if err := c.connPool.RPC(region, addr, "Status.Members", rpcargs, &membersResp); err != nil {
-				mErr.Errors = append(mErr.Errors, err)
-				continue
-			}
-			for _, member := range membersResp.Members {
-				if addrTag, ok := member.Tags["rpc_addr"]; ok {
-					if portTag, ok := member.Tags["port"]; ok {
-						addr, err := net.ResolveTCPAddr("tcp",
-							fmt.Sprintf("%s:%s", addrTag, portTag))
-						if err != nil {
-							mErr.Errors = append(mErr.Errors, err)
-							continue
-						}
-						srv := &servers.Server{Addr: addr}
-						nomadServers = append(nomadServers, srv)
-					}
-				}
-			}
-
-			if len(nomadServers) > 0 {
-				break DISCOLOOP
-			}
+			srv := &servers.Server{Addr: addr}
+			nomadServers = append(nomadServers, srv)
 		}
+
+		if len(nomadServers) > 0 {
+			break DISCOLOOP
+		}
+
 	}
 	if len(nomadServers) == 0 {
 		if len(mErr.Errors) > 0 {