open-consul/agent/consul/rpc.go

947 lines
27 KiB
Go

package consul
import (
"context"
"crypto/tls"
"encoding/binary"
"errors"
"fmt"
"io"
"net"
"strings"
"sync/atomic"
"time"
"github.com/armon/go-metrics"
"github.com/armon/go-metrics/prometheus"
"github.com/hashicorp/consul/acl"
"github.com/hashicorp/consul/agent/consul/state"
"github.com/hashicorp/consul/agent/consul/wanfed"
"github.com/hashicorp/consul/agent/metadata"
"github.com/hashicorp/consul/agent/pool"
"github.com/hashicorp/consul/agent/structs"
"github.com/hashicorp/consul/lib"
"github.com/hashicorp/consul/logging"
connlimit "github.com/hashicorp/go-connlimit"
"github.com/hashicorp/go-hclog"
memdb "github.com/hashicorp/go-memdb"
"github.com/hashicorp/go-raftchunking"
"github.com/hashicorp/memberlist"
msgpackrpc "github.com/hashicorp/net-rpc-msgpackrpc"
"github.com/hashicorp/raft"
"github.com/hashicorp/yamux"
)
var RPCCounters = []prometheus.CounterDefinition{
{
Name: []string{"rpc", "accept_conn"},
Help: "Increments when a server accepts an RPC connection.",
},
{
Name: []string{"rpc", "raft_handoff"},
Help: "Increments when a server accepts a Raft-related RPC connection.",
},
{
Name: []string{"rpc", "request_error"},
Help: "Increments when a server returns an error from an RPC request.",
},
{
Name: []string{"rpc", "request"},
Help: "Increments when a server receives a Consul-related RPC request.",
},
{
Name: []string{"rpc", "cross-dc"},
Help: "Increments when a server sends a (potentially blocking) cross datacenter RPC query.",
},
{
Name: []string{"rpc", "query"},
Help: "Increments when a server receives a new blocking RPC request, indicating the rate of new blocking query calls.",
},
}
var RPCGauges = []prometheus.GaugeDefinition{
{
Name: []string{"rpc", "queries_blocking"},
Help: "Shows the current number of in-flight blocking queries the server is handling.",
},
}
var RPCSummaries = []prometheus.SummaryDefinition{
{
Name: []string{"rpc", "consistentRead"},
Help: "Measures the time spent confirming that a consistent read can be performed.",
},
}
const (
// jitterFraction is a the limit to the amount of jitter we apply
// to a user specified MaxQueryTime. We divide the specified time by
// the fraction. So 16 == 6.25% limit of jitter. This same fraction
// is applied to the RPCHoldTimeout
jitterFraction = 16
// Warn if the Raft command is larger than this.
// If it's over 1MB something is probably being abusive.
raftWarnSize = 1024 * 1024
// enqueueLimit caps how long we will wait to enqueue
// a new Raft command. Something is probably wrong if this
// value is ever reached. However, it prevents us from blocking
// the requesting goroutine forever.
enqueueLimit = 30 * time.Second
)
var (
ErrChunkingResubmit = errors.New("please resubmit call for rechunking")
)
func (s *Server) rpcLogger() hclog.Logger {
return s.loggers.Named(logging.RPC)
}
// listen is used to listen for incoming RPC connections
func (s *Server) listen(listener net.Listener) {
for {
// Accept a connection
conn, err := listener.Accept()
if err != nil {
if s.shutdown {
return
}
s.rpcLogger().Error("failed to accept RPC conn", "error", err)
continue
}
free, err := s.rpcConnLimiter.Accept(conn)
if err != nil {
s.rpcLogger().Error("rejecting RPC conn from because rpc_max_conns_per_client exceeded", "conn", logConn(conn))
conn.Close()
continue
}
// Wrap conn so it will be auto-freed from conn limiter when it closes.
conn = connlimit.Wrap(conn, free)
go s.handleConn(conn, false)
metrics.IncrCounter([]string{"rpc", "accept_conn"}, 1)
}
}
// logConn is a wrapper around memberlist's LogConn so that we format references
// to "from" addresses in a consistent way. This is just a shorter name.
func logConn(conn net.Conn) string {
return memberlist.LogConn(conn)
}
// handleConn is used to determine if this is a Raft or
// Consul type RPC connection and invoke the correct handler
func (s *Server) handleConn(conn net.Conn, isTLS bool) {
// Limit how long the client can hold the connection open before they send the
// magic byte (and authenticate when mTLS is enabled). If `isTLS == true` then
// this also enforces a timeout on how long it takes for the handshake to
// complete since tls.Conn.Read implicitly calls Handshake().
if s.config.RPCHandshakeTimeout > 0 {
conn.SetReadDeadline(time.Now().Add(s.config.RPCHandshakeTimeout))
}
if !isTLS && s.tlsConfigurator.MutualTLSCapable() {
// See if actually this is native TLS multiplexed onto the old
// "type-byte" system.
peekedConn, nativeTLS, err := pool.PeekForTLS(conn)
if err != nil {
if err != io.EOF {
s.rpcLogger().Error(
"failed to read first byte",
"conn", logConn(conn),
"error", err,
)
}
conn.Close()
return
}
if nativeTLS {
s.handleNativeTLS(peekedConn)
return
}
conn = peekedConn
}
// Read a single byte
buf := make([]byte, 1)
if _, err := conn.Read(buf); err != nil {
if err != io.EOF {
s.rpcLogger().Error("failed to read byte",
"conn", logConn(conn),
"error", err,
)
}
conn.Close()
return
}
typ := pool.RPCType(buf[0])
// Reset the deadline as we aren't sure what is expected next - it depends on
// the protocol.
if s.config.RPCHandshakeTimeout > 0 {
conn.SetReadDeadline(time.Time{})
}
// Enforce TLS if VerifyIncoming is set
if s.tlsConfigurator.VerifyIncomingRPC() && !isTLS && typ != pool.RPCTLS && typ != pool.RPCTLSInsecure {
s.rpcLogger().Warn("Non-TLS connection attempted with VerifyIncoming set", "conn", logConn(conn))
conn.Close()
return
}
// Switch on the byte
switch typ {
case pool.RPCConsul:
s.handleConsulConn(conn)
case pool.RPCRaft:
metrics.IncrCounter([]string{"rpc", "raft_handoff"}, 1)
s.raftLayer.Handoff(conn)
case pool.RPCTLS:
// Don't allow malicious client to create TLS-in-TLS for ever.
if isTLS {
s.rpcLogger().Error("TLS connection attempting to establish inner TLS connection", "conn", logConn(conn))
conn.Close()
return
}
conn = tls.Server(conn, s.tlsConfigurator.IncomingRPCConfig())
s.handleConn(conn, true)
case pool.RPCMultiplexV2:
s.handleMultiplexV2(conn)
case pool.RPCSnapshot:
s.handleSnapshotConn(conn)
case pool.RPCTLSInsecure:
// Don't allow malicious client to create TLS-in-TLS for ever.
if isTLS {
s.rpcLogger().Error("TLS connection attempting to establish inner TLS connection", "conn", logConn(conn))
conn.Close()
return
}
conn = tls.Server(conn, s.tlsConfigurator.IncomingInsecureRPCConfig())
s.handleInsecureConn(conn)
case pool.RPCGRPC:
s.grpcHandler.Handle(conn)
default:
if !s.handleEnterpriseRPCConn(typ, conn, isTLS) {
s.rpcLogger().Error("unrecognized RPC byte",
"byte", typ,
"conn", logConn(conn),
)
conn.Close()
}
}
}
func (s *Server) handleNativeTLS(conn net.Conn) {
s.rpcLogger().Trace(
"detected actual TLS over RPC port",
"conn", logConn(conn),
)
tlscfg := s.tlsConfigurator.IncomingALPNRPCConfig(pool.RPCNextProtos)
tlsConn := tls.Server(conn, tlscfg)
// Force the handshake to conclude.
if err := tlsConn.Handshake(); err != nil {
s.rpcLogger().Error(
"TLS handshake failed",
"conn", logConn(conn),
"error", err,
)
conn.Close()
return
}
// Reset the deadline as we aren't sure what is expected next - it depends on
// the protocol.
if s.config.RPCHandshakeTimeout > 0 {
conn.SetReadDeadline(time.Time{})
}
var (
cs = tlsConn.ConnectionState()
sni = cs.ServerName
nextProto = cs.NegotiatedProtocol
transport = s.memberlistTransportWAN
)
s.rpcLogger().Trace(
"accepted nativeTLS RPC",
"sni", sni,
"protocol", nextProto,
"conn", logConn(conn),
)
switch nextProto {
case pool.ALPN_RPCConsul:
s.handleConsulConn(tlsConn)
case pool.ALPN_RPCRaft:
metrics.IncrCounter([]string{"rpc", "raft_handoff"}, 1)
s.raftLayer.Handoff(tlsConn)
case pool.ALPN_RPCMultiplexV2:
s.handleMultiplexV2(tlsConn)
case pool.ALPN_RPCSnapshot:
s.handleSnapshotConn(tlsConn)
case pool.ALPN_RPCGRPC:
s.grpcHandler.Handle(conn)
case pool.ALPN_WANGossipPacket:
if err := s.handleALPN_WANGossipPacketStream(tlsConn); err != nil && err != io.EOF {
s.rpcLogger().Error(
"failed to ingest RPC",
"sni", sni,
"protocol", nextProto,
"conn", logConn(conn),
"error", err,
)
}
case pool.ALPN_WANGossipStream:
// No need to defer the conn.Close() here, the Ingest methods do that.
if err := transport.IngestStream(tlsConn); err != nil {
s.rpcLogger().Error(
"failed to ingest RPC",
"sni", sni,
"protocol", nextProto,
"conn", logConn(conn),
"error", err,
)
}
default:
if !s.handleEnterpriseNativeTLSConn(nextProto, conn) {
s.rpcLogger().Error(
"discarding RPC for unknown negotiated protocol",
"failed to ingest RPC",
"protocol", nextProto,
"conn", logConn(conn),
)
conn.Close()
}
}
}
// handleMultiplexV2 is used to multiplex a single incoming connection
// using the Yamux multiplexer
func (s *Server) handleMultiplexV2(conn net.Conn) {
defer conn.Close()
conf := yamux.DefaultConfig()
// override the default because LogOutput conflicts with Logger
conf.LogOutput = nil
// TODO: should this be created once and cached?
conf.Logger = s.logger.StandardLogger(&hclog.StandardLoggerOptions{InferLevels: true})
server, _ := yamux.Server(conn, conf)
for {
sub, err := server.Accept()
if err != nil {
if err != io.EOF {
s.rpcLogger().Error("multiplex conn accept failed",
"conn", logConn(conn),
"error", err,
)
}
return
}
// In the beginning only RPC was supposed to be multiplexed
// with yamux. In order to add the ability to multiplex network
// area connections, this workaround was added.
// This code peeks the first byte and checks if it is
// RPCGossip, in which case this is handled by enterprise code.
// Otherwise this connection is handled like before by the RPC
// handler.
// This wouldn't work if a normal RPC could start with
// RPCGossip(6). In messagepack a 6 encodes a positive fixint:
// https://github.com/msgpack/msgpack/blob/master/spec.md.
// None of the RPCs we are doing starts with that, usually it is
// a string for datacenter.
peeked, first, err := pool.PeekFirstByte(sub)
if err != nil {
s.rpcLogger().Error("Problem peeking connection", "conn", logConn(sub), "err", err)
sub.Close()
return
}
sub = peeked
switch first {
case pool.RPCGossip:
buf := make([]byte, 1)
sub.Read(buf)
go func() {
if !s.handleEnterpriseRPCConn(pool.RPCGossip, sub, false) {
s.rpcLogger().Error("unrecognized RPC byte",
"byte", pool.RPCGossip,
"conn", logConn(conn),
)
sub.Close()
}
}()
default:
go s.handleConsulConn(sub)
}
}
}
// handleConsulConn is used to service a single Consul RPC connection
func (s *Server) handleConsulConn(conn net.Conn) {
defer conn.Close()
rpcCodec := msgpackrpc.NewCodecFromHandle(true, true, conn, structs.MsgpackHandle)
for {
select {
case <-s.shutdownCh:
return
default:
}
if err := s.rpcServer.ServeRequest(rpcCodec); err != nil {
if err != io.EOF && !strings.Contains(err.Error(), "closed") {
s.rpcLogger().Error("RPC error",
"conn", logConn(conn),
"error", err,
)
metrics.IncrCounter([]string{"rpc", "request_error"}, 1)
}
return
}
metrics.IncrCounter([]string{"rpc", "request"}, 1)
}
}
// handleInsecureConsulConn is used to service a single Consul INSECURERPC connection
func (s *Server) handleInsecureConn(conn net.Conn) {
defer conn.Close()
rpcCodec := msgpackrpc.NewCodecFromHandle(true, true, conn, structs.MsgpackHandle)
for {
select {
case <-s.shutdownCh:
return
default:
}
if err := s.insecureRPCServer.ServeRequest(rpcCodec); err != nil {
if err != io.EOF && !strings.Contains(err.Error(), "closed") {
s.rpcLogger().Error("INSECURERPC error",
"conn", logConn(conn),
"error", err,
)
metrics.IncrCounter([]string{"rpc", "request_error"}, 1)
}
return
}
metrics.IncrCounter([]string{"rpc", "request"}, 1)
}
}
// handleSnapshotConn is used to dispatch snapshot saves and restores, which
// stream so don't use the normal RPC mechanism.
func (s *Server) handleSnapshotConn(conn net.Conn) {
go func() {
defer conn.Close()
if err := s.handleSnapshotRequest(conn); err != nil {
s.rpcLogger().Error("Snapshot RPC error",
"conn", logConn(conn),
"error", err,
)
}
}()
}
func (s *Server) handleALPN_WANGossipPacketStream(conn net.Conn) error {
defer conn.Close()
transport := s.memberlistTransportWAN
for {
select {
case <-s.shutdownCh:
return nil
default:
}
// Note: if we need to change this format to have additional header
// information we can just negotiate a different ALPN protocol instead
// of needing any sort of version field here.
prefixLen, err := readUint32(conn, wanfed.GossipPacketMaxIdleTime)
if err != nil {
return err
}
// Avoid a memory exhaustion DOS vector here by capping how large this
// packet can be to something reasonable.
if prefixLen > wanfed.GossipPacketMaxByteSize {
return fmt.Errorf("gossip packet size %d exceeds threshold of %d", prefixLen, wanfed.GossipPacketMaxByteSize)
}
lc := &limitedConn{
Conn: conn,
lr: io.LimitReader(conn, int64(prefixLen)),
}
if err := transport.IngestPacket(lc, conn.RemoteAddr(), time.Now(), false); err != nil {
return err
}
}
}
func readUint32(conn net.Conn, timeout time.Duration) (uint32, error) {
// Since requests are framed we can easily just set a deadline on
// reading that frame and then disable it for the rest of the body.
if err := conn.SetReadDeadline(time.Now().Add(timeout)); err != nil {
return 0, err
}
var v uint32
if err := binary.Read(conn, binary.BigEndian, &v); err != nil {
return 0, err
}
if err := conn.SetReadDeadline(time.Time{}); err != nil {
return 0, err
}
return v, nil
}
type limitedConn struct {
net.Conn
lr io.Reader
}
func (c *limitedConn) Read(b []byte) (n int, err error) {
return c.lr.Read(b)
}
// canRetry returns true if the given situation is safe for a retry.
func canRetry(args interface{}, err error) bool {
// No leader errors are always safe to retry since no state could have
// been changed.
if structs.IsErrNoLeader(err) {
return true
}
// If we are chunking and it doesn't seem to have completed, try again
intErr, ok := args.(error)
if ok && strings.Contains(intErr.Error(), ErrChunkingResubmit.Error()) {
return true
}
// Reads are safe to retry for stream errors, such as if a server was
// being shut down.
info, ok := args.(structs.RPCInfo)
if ok && info.IsRead() && lib.IsErrEOF(err) {
return true
}
return false
}
// ForwardRPC is used to forward an RPC request to a remote DC or to the local leader
// Returns a bool of if forwarding was performed, as well as any error
func (s *Server) ForwardRPC(method string, info structs.RPCInfo, args interface{}, reply interface{}) (bool, error) {
var firstCheck time.Time
// Handle DC forwarding
dc := info.RequestDatacenter()
if dc != s.config.Datacenter {
// Local tokens only work within the current datacenter. Check to see
// if we are attempting to forward one to a remote datacenter and strip
// it, falling back on the anonymous token on the other end.
if token := info.TokenSecret(); token != "" {
done, ident, err := s.ResolveIdentityFromToken(token)
if done {
if err != nil && !acl.IsErrNotFound(err) {
return false, err
}
if ident != nil && ident.IsLocal() {
// Strip it from the request.
info.SetTokenSecret("")
defer info.SetTokenSecret(token)
}
}
}
err := s.forwardDC(method, dc, args, reply)
return true, err
}
// Check if we can allow a stale read, ensure our local DB is initialized
if info.IsRead() && info.AllowStaleRead() && !s.raft.LastContact().IsZero() {
return false, nil
}
CHECK_LEADER:
// Fail fast if we are in the process of leaving
select {
case <-s.leaveCh:
return true, structs.ErrNoLeader
default:
}
// Find the leader
isLeader, leader := s.getLeader()
// Handle the case we are the leader
if isLeader {
return false, nil
}
// Handle the case of a known leader
rpcErr := structs.ErrNoLeader
if leader != nil {
rpcErr = s.connPool.RPC(s.config.Datacenter, leader.ShortName, leader.Addr,
method, args, reply)
if rpcErr != nil && canRetry(info, rpcErr) {
goto RETRY
}
return true, rpcErr
}
RETRY:
// Gate the request until there is a leader
if firstCheck.IsZero() {
firstCheck = time.Now()
}
if time.Since(firstCheck) < s.config.RPCHoldTimeout {
jitter := lib.RandomStagger(s.config.RPCHoldTimeout / jitterFraction)
select {
case <-time.After(jitter):
goto CHECK_LEADER
case <-s.leaveCh:
case <-s.shutdownCh:
}
}
// No leader found and hold time exceeded
return true, rpcErr
}
// getLeader returns if the current node is the leader, and if not then it
// returns the leader which is potentially nil if the cluster has not yet
// elected a leader.
func (s *Server) getLeader() (bool, *metadata.Server) {
// Check if we are the leader
if s.IsLeader() {
return true, nil
}
// Get the leader
leader := s.raft.Leader()
if leader == "" {
return false, nil
}
// Lookup the server
server := s.serverLookup.Server(leader)
// Server could be nil
return false, server
}
// forwardDC is used to forward an RPC call to a remote DC, or fail if no servers
func (s *Server) forwardDC(method, dc string, args interface{}, reply interface{}) error {
manager, server, ok := s.router.FindRoute(dc)
if !ok {
if s.router.HasDatacenter(dc) {
s.rpcLogger().Warn("RPC request to DC is currently failing as no server can be reached", "datacenter", dc)
return structs.ErrDCNotAvailable
}
s.rpcLogger().Warn("RPC request for DC is currently failing as no path was found",
"datacenter", dc,
"method", method,
)
return structs.ErrNoDCPath
}
metrics.IncrCounterWithLabels([]string{"rpc", "cross-dc"}, 1,
[]metrics.Label{{Name: "datacenter", Value: dc}})
if err := s.connPool.RPC(dc, server.ShortName, server.Addr, method, args, reply); err != nil {
manager.NotifyFailedServer(server)
s.rpcLogger().Error("RPC failed to server in DC",
"server", server.Addr,
"datacenter", dc,
"method", method,
"error", err,
)
return err
}
return nil
}
// keyringRPCs is used to forward an RPC request to a server in each dc. This
// will only error for RPC-related errors. Otherwise, application-level errors
// can be sent in the response objects.
func (s *Server) keyringRPCs(method string, args interface{}, dcs []string) (*structs.KeyringResponses, error) {
errorCh := make(chan error, len(dcs))
respCh := make(chan *structs.KeyringResponses, len(dcs))
for _, dc := range dcs {
go func(dc string) {
rr := &structs.KeyringResponses{}
if err := s.forwardDC(method, dc, args, &rr); err != nil {
errorCh <- err
return
}
respCh <- rr
}(dc)
}
responses := &structs.KeyringResponses{}
for i := 0; i < len(dcs); i++ {
select {
case err := <-errorCh:
return nil, err
case rr := <-respCh:
responses.Add(rr)
}
}
return responses, nil
}
type raftEncoder func(structs.MessageType, interface{}) ([]byte, error)
// raftApply is used to encode a message, run it through raft, and return
// the FSM response along with any errors
func (s *Server) raftApply(t structs.MessageType, msg interface{}) (interface{}, error) {
return s.raftApplyMsgpack(t, msg)
}
// raftApplyMsgpack will msgpack encode the request and then run it through raft,
// then return the FSM response along with any errors.
func (s *Server) raftApplyMsgpack(t structs.MessageType, msg interface{}) (interface{}, error) {
return s.raftApplyWithEncoder(t, msg, structs.Encode)
}
// raftApplyProtobuf will protobuf encode the request and then run it through raft,
// then return the FSM response along with any errors.
func (s *Server) raftApplyProtobuf(t structs.MessageType, msg interface{}) (interface{}, error) {
return s.raftApplyWithEncoder(t, msg, structs.EncodeProtoInterface)
}
// raftApplyWithEncoder is used to encode a message, run it through raft,
// and return the FSM response along with any errors. Unlike raftApply this
// takes the encoder to use as an argument.
func (s *Server) raftApplyWithEncoder(t structs.MessageType, msg interface{}, encoder raftEncoder) (interface{}, error) {
if encoder == nil {
return nil, fmt.Errorf("Failed to encode request: nil encoder")
}
buf, err := encoder(t, msg)
if err != nil {
return nil, fmt.Errorf("Failed to encode request: %v", err)
}
// Warn if the command is very large
if n := len(buf); n > raftWarnSize {
s.rpcLogger().Warn("Attempting to apply large raft entry", "size_in_bytes", n)
}
var chunked bool
var future raft.ApplyFuture
switch {
case len(buf) <= raft.SuggestedMaxDataSize || t != structs.KVSRequestType:
future = s.raft.Apply(buf, enqueueLimit)
default:
chunked = true
future = raftchunking.ChunkingApply(buf, nil, enqueueLimit, s.raft.ApplyLog)
}
if err := future.Error(); err != nil {
return nil, err
}
resp := future.Response()
if chunked {
// In this case we didn't apply all chunks successfully, possibly due
// to a term change; resubmit
if resp == nil {
// This returns the error in the interface because the raft library
// returns errors from the FSM via the future, not via err from the
// apply function. Downstream client code expects to see any error
// from the FSM (as opposed to the apply itself) and decide whether
// it can retry in the future's response.
return ErrChunkingResubmit, nil
}
// We expect that this conversion should always work
chunkedSuccess, ok := resp.(raftchunking.ChunkingSuccess)
if !ok {
return nil, errors.New("unknown type of response back from chunking FSM")
}
// Return the inner wrapped response
return chunkedSuccess.Response, nil
}
return resp, nil
}
// queryFn is used to perform a query operation. If a re-query is needed, the
// passed-in watch set will be used to block for changes. The passed-in state
// store should be used (vs. calling fsm.State()) since the given state store
// will be correctly watched for changes if the state store is restored from
// a snapshot.
type queryFn func(memdb.WatchSet, *state.Store) error
// blockingQuery is used to process a potentially blocking query operation.
func (s *Server) blockingQuery(queryOpts structs.QueryOptionsCompat, queryMeta structs.QueryMetaCompat, fn queryFn) error {
var cancel func()
var ctx context.Context = &lib.StopChannelContext{StopCh: s.shutdownCh}
var queriesBlocking uint64
var queryTimeout time.Duration
// Instrument all queries run
metrics.IncrCounter([]string{"rpc", "query"}, 1)
minQueryIndex := queryOpts.GetMinQueryIndex()
// Fast path right to the non-blocking query.
if minQueryIndex == 0 {
goto RUN_QUERY
}
queryTimeout = queryOpts.GetMaxQueryTime()
// Restrict the max query time, and ensure there is always one.
if queryTimeout > s.config.MaxQueryTime {
queryTimeout = s.config.MaxQueryTime
} else if queryTimeout <= 0 {
queryTimeout = s.config.DefaultQueryTime
}
// Apply a small amount of jitter to the request.
queryTimeout += lib.RandomStagger(queryTimeout / jitterFraction)
// wrap the base context with a deadline
ctx, cancel = context.WithDeadline(ctx, time.Now().Add(queryTimeout))
defer cancel()
// instrument blockingQueries
// atomic inc our server's count of in-flight blockingQueries and store the new value
queriesBlocking = atomic.AddUint64(&s.queriesBlocking, 1)
// atomic dec when we return from blockingQuery()
defer atomic.AddUint64(&s.queriesBlocking, ^uint64(0))
// set the gauge directly to the new value of s.blockingQueries
metrics.SetGauge([]string{"rpc", "queries_blocking"}, float32(queriesBlocking))
RUN_QUERY:
// Setup blocking loop
// Update the query metadata.
s.setQueryMeta(queryMeta)
// Validate
// If the read must be consistent we verify that we are still the leader.
if queryOpts.GetRequireConsistent() {
if err := s.consistentRead(); err != nil {
return err
}
}
// Run query
// Operate on a consistent set of state. This makes sure that the
// abandon channel goes with the state that the caller is using to
// build watches.
state := s.fsm.State()
// We can skip all watch tracking if this isn't a blocking query.
var ws memdb.WatchSet
if minQueryIndex > 0 {
ws = memdb.NewWatchSet()
// This channel will be closed if a snapshot is restored and the
// whole state store is abandoned.
ws.Add(state.AbandonCh())
}
// Execute the queryFn
err := fn(ws, state)
// Note we check queryOpts.MinQueryIndex is greater than zero to determine if
// blocking was requested by client, NOT meta.Index since the state function
// might return zero if something is not initialized and care wasn't taken to
// handle that special case (in practice this happened a lot so fixing it
// systematically here beats trying to remember to add zero checks in every
// state method). We also need to ensure that unless there is an error, we
// return an index > 0 otherwise the client will never block and burn CPU and
// requests.
if err == nil && queryMeta.GetIndex() < 1 {
queryMeta.SetIndex(1)
}
// block up to the timeout if we don't see anything fresh.
if err == nil && minQueryIndex > 0 && queryMeta.GetIndex() <= minQueryIndex {
if err := ws.WatchCtx(ctx); err == nil {
// a non-nil error only occurs when the context is cancelled
// If a restore may have woken us up then bail out from
// the query immediately. This is slightly race-ey since
// this might have been interrupted for other reasons,
// but it's OK to kick it back to the caller in either
// case.
select {
case <-state.AbandonCh():
default:
// loop back and look for an update again
goto RUN_QUERY
}
}
}
return err
}
// setQueryMeta is used to populate the QueryMeta data for an RPC call
func (s *Server) setQueryMeta(m structs.QueryMetaCompat) {
if s.IsLeader() {
m.SetLastContact(0)
m.SetKnownLeader(true)
} else {
m.SetLastContact(time.Since(s.raft.LastContact()))
m.SetKnownLeader(s.raft.Leader() != "")
}
}
// consistentRead is used to ensure we do not perform a stale
// read. This is done by verifying leadership before the read.
func (s *Server) consistentRead() error {
defer metrics.MeasureSince([]string{"rpc", "consistentRead"}, time.Now())
future := s.raft.VerifyLeader()
if err := future.Error(); err != nil {
return err //fail fast if leader verification fails
}
// poll consistent read readiness, wait for up to RPCHoldTimeout milliseconds
if s.isReadyForConsistentReads() {
return nil
}
jitter := lib.RandomStagger(s.config.RPCHoldTimeout / jitterFraction)
deadline := time.Now().Add(s.config.RPCHoldTimeout)
for time.Now().Before(deadline) {
select {
case <-time.After(jitter):
// Drop through and check before we loop again.
case <-s.shutdownCh:
return fmt.Errorf("shutdown waiting for leader")
}
if s.isReadyForConsistentReads() {
return nil
}
}
return structs.ErrNotReadyForConsistentReads
}