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grpclb.go
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grpclb.go
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/*
*
* Copyright 2016 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
// Package grpclb defines a grpclb balancer.
//
// To install grpclb balancer, import this package as:
//
// import _ "google.golang.org/grpc/balancer/grpclb"
package grpclb
import (
"context"
"errors"
"fmt"
"sync"
"time"
"google.golang.org/grpc"
"google.golang.org/grpc/balancer"
grpclbstate "google.golang.org/grpc/balancer/grpclb/state"
"google.golang.org/grpc/connectivity"
"google.golang.org/grpc/credentials"
"google.golang.org/grpc/grpclog"
"google.golang.org/grpc/internal"
"google.golang.org/grpc/internal/backoff"
"google.golang.org/grpc/internal/resolver/dns"
"google.golang.org/grpc/resolver"
durationpb "github.com/golang/protobuf/ptypes/duration"
lbpb "google.golang.org/grpc/balancer/grpclb/grpc_lb_v1"
)
const (
lbTokenKey = "lb-token"
defaultFallbackTimeout = 10 * time.Second
grpclbName = "grpclb"
)
var errServerTerminatedConnection = errors.New("grpclb: failed to recv server list: server terminated connection")
var logger = grpclog.Component("grpclb")
func convertDuration(d *durationpb.Duration) time.Duration {
if d == nil {
return 0
}
return time.Duration(d.Seconds)*time.Second + time.Duration(d.Nanos)*time.Nanosecond
}
// Client API for LoadBalancer service.
// Mostly copied from generated pb.go file.
// To avoid circular dependency.
type loadBalancerClient struct {
cc *grpc.ClientConn
}
func (c *loadBalancerClient) BalanceLoad(ctx context.Context, opts ...grpc.CallOption) (*balanceLoadClientStream, error) {
desc := &grpc.StreamDesc{
StreamName: "BalanceLoad",
ServerStreams: true,
ClientStreams: true,
}
stream, err := c.cc.NewStream(ctx, desc, "/grpc.lb.v1.LoadBalancer/BalanceLoad", opts...)
if err != nil {
return nil, err
}
x := &balanceLoadClientStream{stream}
return x, nil
}
type balanceLoadClientStream struct {
grpc.ClientStream
}
func (x *balanceLoadClientStream) Send(m *lbpb.LoadBalanceRequest) error {
return x.ClientStream.SendMsg(m)
}
func (x *balanceLoadClientStream) Recv() (*lbpb.LoadBalanceResponse, error) {
m := new(lbpb.LoadBalanceResponse)
if err := x.ClientStream.RecvMsg(m); err != nil {
return nil, err
}
return m, nil
}
func init() {
balancer.Register(newLBBuilder())
dns.EnableSRVLookups = true
}
// newLBBuilder creates a builder for grpclb.
func newLBBuilder() balancer.Builder {
return newLBBuilderWithFallbackTimeout(defaultFallbackTimeout)
}
// newLBBuilderWithFallbackTimeout creates a grpclb builder with the given
// fallbackTimeout. If no response is received from the remote balancer within
// fallbackTimeout, the backend addresses from the resolved address list will be
// used.
//
// Only call this function when a non-default fallback timeout is needed.
func newLBBuilderWithFallbackTimeout(fallbackTimeout time.Duration) balancer.Builder {
return &lbBuilder{
fallbackTimeout: fallbackTimeout,
}
}
type lbBuilder struct {
fallbackTimeout time.Duration
}
func (b *lbBuilder) Name() string {
return grpclbName
}
func (b *lbBuilder) Build(cc balancer.ClientConn, opt balancer.BuildOptions) balancer.Balancer {
// This generates a manual resolver builder with a fixed scheme. This
// scheme will be used to dial to remote LB, so we can send filtered
// address updates to remote LB ClientConn using this manual resolver.
r := &lbManualResolver{scheme: "grpclb-internal", ccb: cc}
lb := &lbBalancer{
cc: newLBCacheClientConn(cc),
dialTarget: opt.Target.Endpoint(),
target: opt.Target.Endpoint(),
opt: opt,
fallbackTimeout: b.fallbackTimeout,
doneCh: make(chan struct{}),
manualResolver: r,
subConns: make(map[resolver.Address]balancer.SubConn),
scStates: make(map[balancer.SubConn]connectivity.State),
picker: &errPicker{err: balancer.ErrNoSubConnAvailable},
clientStats: newRPCStats(),
backoff: backoff.DefaultExponential, // TODO: make backoff configurable.
}
var err error
if opt.CredsBundle != nil {
lb.grpclbClientConnCreds, err = opt.CredsBundle.NewWithMode(internal.CredsBundleModeBalancer)
if err != nil {
logger.Warningf("lbBalancer: client connection creds NewWithMode failed: %v", err)
}
lb.grpclbBackendCreds, err = opt.CredsBundle.NewWithMode(internal.CredsBundleModeBackendFromBalancer)
if err != nil {
logger.Warningf("lbBalancer: backend creds NewWithMode failed: %v", err)
}
}
return lb
}
type lbBalancer struct {
cc *lbCacheClientConn
dialTarget string // user's dial target
target string // same as dialTarget unless overridden in service config
opt balancer.BuildOptions
usePickFirst bool
// grpclbClientConnCreds is the creds bundle to be used to connect to grpclb
// servers. If it's nil, use the TransportCredentials from BuildOptions
// instead.
grpclbClientConnCreds credentials.Bundle
// grpclbBackendCreds is the creds bundle to be used for addresses that are
// returned by grpclb server. If it's nil, don't set anything when creating
// SubConns.
grpclbBackendCreds credentials.Bundle
fallbackTimeout time.Duration
doneCh chan struct{}
// manualResolver is used in the remote LB ClientConn inside grpclb. When
// resolved address updates are received by grpclb, filtered updates will be
// send to remote LB ClientConn through this resolver.
manualResolver *lbManualResolver
// The ClientConn to talk to the remote balancer.
ccRemoteLB *remoteBalancerCCWrapper
// backoff for calling remote balancer.
backoff backoff.Strategy
// Support client side load reporting. Each picker gets a reference to this,
// and will update its content.
clientStats *rpcStats
mu sync.Mutex // guards everything following.
// The full server list including drops, used to check if the newly received
// serverList contains anything new. Each generate picker will also have
// reference to this list to do the first layer pick.
fullServerList []*lbpb.Server
// Backend addresses. It's kept so the addresses are available when
// switching between round_robin and pickfirst.
backendAddrs []resolver.Address
// All backends addresses, with metadata set to nil. This list contains all
// backend addresses in the same order and with the same duplicates as in
// serverlist. When generating picker, a SubConn slice with the same order
// but with only READY SCs will be gerenated.
backendAddrsWithoutMetadata []resolver.Address
// Roundrobin functionalities.
state connectivity.State
subConns map[resolver.Address]balancer.SubConn // Used to new/remove SubConn.
scStates map[balancer.SubConn]connectivity.State // Used to filter READY SubConns.
picker balancer.Picker
// Support fallback to resolved backend addresses if there's no response
// from remote balancer within fallbackTimeout.
remoteBalancerConnected bool
serverListReceived bool
inFallback bool
// resolvedBackendAddrs is resolvedAddrs minus remote balancers. It's set
// when resolved address updates are received, and read in the goroutine
// handling fallback.
resolvedBackendAddrs []resolver.Address
connErr error // the last connection error
}
// regeneratePicker takes a snapshot of the balancer, and generates a picker from
// it. The picker
// - always returns ErrTransientFailure if the balancer is in TransientFailure,
// - does two layer roundrobin pick otherwise.
//
// Caller must hold lb.mu.
func (lb *lbBalancer) regeneratePicker(resetDrop bool) {
if lb.state == connectivity.TransientFailure {
lb.picker = &errPicker{err: fmt.Errorf("all SubConns are in TransientFailure, last connection error: %v", lb.connErr)}
return
}
if lb.state == connectivity.Connecting {
lb.picker = &errPicker{err: balancer.ErrNoSubConnAvailable}
return
}
var readySCs []balancer.SubConn
if lb.usePickFirst {
for _, sc := range lb.subConns {
readySCs = append(readySCs, sc)
break
}
} else {
for _, a := range lb.backendAddrsWithoutMetadata {
if sc, ok := lb.subConns[a]; ok {
if st, ok := lb.scStates[sc]; ok && st == connectivity.Ready {
readySCs = append(readySCs, sc)
}
}
}
}
if len(readySCs) <= 0 {
// If there's no ready SubConns, always re-pick. This is to avoid drops
// unless at least one SubConn is ready. Otherwise we may drop more
// often than want because of drops + re-picks(which become re-drops).
//
// This doesn't seem to be necessary after the connecting check above.
// Kept for safety.
lb.picker = &errPicker{err: balancer.ErrNoSubConnAvailable}
return
}
if lb.inFallback {
lb.picker = newRRPicker(readySCs)
return
}
if resetDrop {
lb.picker = newLBPicker(lb.fullServerList, readySCs, lb.clientStats)
return
}
prevLBPicker, ok := lb.picker.(*lbPicker)
if !ok {
lb.picker = newLBPicker(lb.fullServerList, readySCs, lb.clientStats)
return
}
prevLBPicker.updateReadySCs(readySCs)
}
// aggregateSubConnStats calculate the aggregated state of SubConns in
// lb.SubConns. These SubConns are subconns in use (when switching between
// fallback and grpclb). lb.scState contains states for all SubConns, including
// those in cache (SubConns are cached for 10 seconds after remove).
//
// The aggregated state is:
// - If at least one SubConn in Ready, the aggregated state is Ready;
// - Else if at least one SubConn in Connecting or IDLE, the aggregated state is Connecting;
// - It's OK to consider IDLE as Connecting. SubConns never stay in IDLE,
// they start to connect immediately. But there's a race between the overall
// state is reported, and when the new SubConn state arrives. And SubConns
// never go back to IDLE.
// - Else the aggregated state is TransientFailure.
func (lb *lbBalancer) aggregateSubConnStates() connectivity.State {
var numConnecting uint64
for _, sc := range lb.subConns {
if state, ok := lb.scStates[sc]; ok {
switch state {
case connectivity.Ready:
return connectivity.Ready
case connectivity.Connecting, connectivity.Idle:
numConnecting++
}
}
}
if numConnecting > 0 {
return connectivity.Connecting
}
return connectivity.TransientFailure
}
func (lb *lbBalancer) UpdateSubConnState(sc balancer.SubConn, scs balancer.SubConnState) {
s := scs.ConnectivityState
if logger.V(2) {
logger.Infof("lbBalancer: handle SubConn state change: %p, %v", sc, s)
}
lb.mu.Lock()
defer lb.mu.Unlock()
oldS, ok := lb.scStates[sc]
if !ok {
if logger.V(2) {
logger.Infof("lbBalancer: got state changes for an unknown SubConn: %p, %v", sc, s)
}
return
}
lb.scStates[sc] = s
switch s {
case connectivity.Idle:
sc.Connect()
case connectivity.Shutdown:
// When an address was removed by resolver, b called RemoveSubConn but
// kept the sc's state in scStates. Remove state for this sc here.
delete(lb.scStates, sc)
case connectivity.TransientFailure:
lb.connErr = scs.ConnectionError
}
// Force regenerate picker if
// - this sc became ready from not-ready
// - this sc became not-ready from ready
lb.updateStateAndPicker((oldS == connectivity.Ready) != (s == connectivity.Ready), false)
// Enter fallback when the aggregated state is not Ready and the connection
// to remote balancer is lost.
if lb.state != connectivity.Ready {
if !lb.inFallback && !lb.remoteBalancerConnected {
// Enter fallback.
lb.refreshSubConns(lb.resolvedBackendAddrs, true, lb.usePickFirst)
}
}
}
// updateStateAndPicker re-calculate the aggregated state, and regenerate picker
// if overall state is changed.
//
// If forceRegeneratePicker is true, picker will be regenerated.
func (lb *lbBalancer) updateStateAndPicker(forceRegeneratePicker bool, resetDrop bool) {
oldAggrState := lb.state
lb.state = lb.aggregateSubConnStates()
// Regenerate picker when one of the following happens:
// - caller wants to regenerate
// - the aggregated state changed
if forceRegeneratePicker || (lb.state != oldAggrState) {
lb.regeneratePicker(resetDrop)
}
lb.cc.UpdateState(balancer.State{ConnectivityState: lb.state, Picker: lb.picker})
}
// fallbackToBackendsAfter blocks for fallbackTimeout and falls back to use
// resolved backends (backends received from resolver, not from remote balancer)
// if no connection to remote balancers was successful.
func (lb *lbBalancer) fallbackToBackendsAfter(fallbackTimeout time.Duration) {
timer := time.NewTimer(fallbackTimeout)
defer timer.Stop()
select {
case <-timer.C:
case <-lb.doneCh:
return
}
lb.mu.Lock()
if lb.inFallback || lb.serverListReceived {
lb.mu.Unlock()
return
}
// Enter fallback.
lb.refreshSubConns(lb.resolvedBackendAddrs, true, lb.usePickFirst)
lb.mu.Unlock()
}
func (lb *lbBalancer) handleServiceConfig(gc *grpclbServiceConfig) {
lb.mu.Lock()
defer lb.mu.Unlock()
// grpclb uses the user's dial target to populate the `Name` field of the
// `InitialLoadBalanceRequest` message sent to the remote balancer. But when
// grpclb is used a child policy in the context of RLS, we want the `Name`
// field to be populated with the value received from the RLS server. To
// support this use case, an optional "target_name" field has been added to
// the grpclb LB policy's config. If specified, it overrides the name of
// the target to be sent to the remote balancer; if not, the target to be
// sent to the balancer will continue to be obtained from the target URI
// passed to the gRPC client channel. Whenever that target to be sent to the
// balancer is updated, we need to restart the stream to the balancer as
// this target is sent in the first message on the stream.
if gc != nil {
target := lb.dialTarget
if gc.ServiceName != "" {
target = gc.ServiceName
}
if target != lb.target {
lb.target = target
if lb.ccRemoteLB != nil {
lb.ccRemoteLB.cancelRemoteBalancerCall()
}
}
}
newUsePickFirst := childIsPickFirst(gc)
if lb.usePickFirst == newUsePickFirst {
return
}
if logger.V(2) {
logger.Infof("lbBalancer: switching mode, new usePickFirst: %+v", newUsePickFirst)
}
lb.refreshSubConns(lb.backendAddrs, lb.inFallback, newUsePickFirst)
}
func (lb *lbBalancer) ResolverError(error) {
// Ignore resolver errors. GRPCLB is not selected unless the resolver
// works at least once.
}
func (lb *lbBalancer) UpdateClientConnState(ccs balancer.ClientConnState) error {
if logger.V(2) {
logger.Infof("lbBalancer: UpdateClientConnState: %+v", ccs)
}
gc, _ := ccs.BalancerConfig.(*grpclbServiceConfig)
lb.handleServiceConfig(gc)
addrs := ccs.ResolverState.Addresses
var remoteBalancerAddrs, backendAddrs []resolver.Address
for _, a := range addrs {
if a.Type == resolver.GRPCLB {
a.Type = resolver.Backend
remoteBalancerAddrs = append(remoteBalancerAddrs, a)
} else {
backendAddrs = append(backendAddrs, a)
}
}
if sd := grpclbstate.Get(ccs.ResolverState); sd != nil {
// Override any balancer addresses provided via
// ccs.ResolverState.Addresses.
remoteBalancerAddrs = sd.BalancerAddresses
}
if len(backendAddrs)+len(remoteBalancerAddrs) == 0 {
// There should be at least one address, either grpclb server or
// fallback. Empty address is not valid.
return balancer.ErrBadResolverState
}
if len(remoteBalancerAddrs) == 0 {
if lb.ccRemoteLB != nil {
lb.ccRemoteLB.close()
lb.ccRemoteLB = nil
}
} else if lb.ccRemoteLB == nil {
// First time receiving resolved addresses, create a cc to remote
// balancers.
lb.newRemoteBalancerCCWrapper()
// Start the fallback goroutine.
go lb.fallbackToBackendsAfter(lb.fallbackTimeout)
}
if lb.ccRemoteLB != nil {
// cc to remote balancers uses lb.manualResolver. Send the updated remote
// balancer addresses to it through manualResolver.
lb.manualResolver.UpdateState(resolver.State{Addresses: remoteBalancerAddrs})
}
lb.mu.Lock()
lb.resolvedBackendAddrs = backendAddrs
if len(remoteBalancerAddrs) == 0 || lb.inFallback {
// If there's no remote balancer address in ClientConn update, grpclb
// enters fallback mode immediately.
//
// If a new update is received while grpclb is in fallback, update the
// list of backends being used to the new fallback backends.
lb.refreshSubConns(lb.resolvedBackendAddrs, true, lb.usePickFirst)
}
lb.mu.Unlock()
return nil
}
func (lb *lbBalancer) Close() {
select {
case <-lb.doneCh:
return
default:
}
close(lb.doneCh)
if lb.ccRemoteLB != nil {
lb.ccRemoteLB.close()
}
lb.cc.close()
}
func (lb *lbBalancer) ExitIdle() {}