gubernator.go

/*
Copyright 2018-2022 Mailgun Technologies Inc

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 gubernator

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"sync/atomic"

	"github.com/mailgun/holster/v4/ctxutil"
	"github.com/mailgun/holster/v4/errors"
	"github.com/mailgun/holster/v4/setter"
	"github.com/mailgun/holster/v4/syncutil"
	"github.com/mailgun/holster/v4/tracing"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/sirupsen/logrus"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
	"google.golang.org/protobuf/proto"
)

const (
	maxBatchSize = 1000
	Healthy      = "healthy"
	UnHealthy    = "unhealthy"
)

type V1Instance struct {
	UnimplementedV1Server
	UnimplementedPeersV1Server
	global               *globalManager
	mutliRegion          *mutliRegionManager
	peerMutex            sync.RWMutex
	log                  logrus.FieldLogger
	conf                 Config
	isClosed             bool
	getRateLimitsCounter int64
	gubernatorPool       *GubernatorPool
}

var getRateLimitCounter = prometheus.NewCounterVec(prometheus.CounterOpts{
	Name: "gubernator_getratelimit_counter",
	Help: "The count of getRateLimit() calls.  Label \"calltype\" may be \"local\" for calls handled by the same peer, \"forward\" for calls forwarded to another peer, or \"global\" for global rate limits.",
}, []string{"calltype"})
var funcTimeMetric = prometheus.NewSummaryVec(prometheus.SummaryOpts{
	Name: "gubernator_func_duration",
	Help: "The timings of key functions in Gubernator in seconds.",
	Objectives: map[float64]float64{
		0.99: 0.001,
	},
}, []string{"name"})
var asyncRequestRetriesCounter = prometheus.NewCounterVec(prometheus.CounterOpts{
	Name: "gubernator_asyncrequest_retries",
	Help: "The count of retries occurred in asyncRequests() forwarding a request to another peer.",
}, []string{"name"})
var queueLengthMetric = prometheus.NewSummaryVec(prometheus.SummaryOpts{
	Name: "gubernator_queue_length",
	Help: "The getRateLimitsBatch() queue length in PeerClient.  This represents rate checks queued by for batching to a remote peer.",
	Objectives: map[float64]float64{
		0.99: 0.001,
	},
}, []string{"peerAddr"})
var checkCounter = prometheus.NewCounter(prometheus.CounterOpts{
	Name: "gubernator_check_counter",
	Help: "The number of rate limits checked.",
})
var overLimitCounter = prometheus.NewCounter(prometheus.CounterOpts{
	Name: "gubernator_over_limit_counter",
	Help: "The number of rate limit checks that are over the limit.",
})
var concurrentChecksMetric = prometheus.NewSummary(prometheus.SummaryOpts{
	Name: "gubernator_concurrent_checks_counter",
	Help: "The number of concurrent GetRateLimits API calls.",
	Objectives: map[float64]float64{
		0.99: 0.001,
	},
})
var checkErrorCounter = prometheus.NewCounterVec(prometheus.CounterOpts{
	Name: "gubernator_check_error_counter",
	Help: "The number of errors while checking rate limits.",
}, []string{"error"})
var poolWorkerQueueLength = prometheus.NewSummaryVec(prometheus.SummaryOpts{
	Name: "gubernator_pool_queue_length",
	Help: "The number of GetRateLimit requests queued up in GubernatorPool workers.",
	Objectives: map[float64]float64{
		0.99: 0.001,
	},
}, []string{"method", "worker"})
var batchSendDurationMetric = prometheus.NewSummaryVec(prometheus.SummaryOpts{
	Name: "gubernator_batch_send_duration",
	Help: "The timings of batch send operations to a remote peer.",
	Objectives: map[float64]float64{
		0.99: 0.001,
	},
}, []string{"peerAddr"})

// NewV1Instance instantiate a single instance of a gubernator peer and registers this
// instance with the provided GRPCServer.
func NewV1Instance(conf Config) (retval *V1Instance, reterr error) {
	ctx := tracing.StartScope(context.Background())
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()

	if conf.GRPCServers == nil {
		return nil, errors.New("at least one GRPCServer instance is required")
	}
	if err := conf.SetDefaults(); err != nil {
		return nil, err
	}

	s := V1Instance{
		log:  conf.Logger,
		conf: conf,
	}
	setter.SetDefault(&s.log, logrus.WithField("category", "gubernator"))

	s.gubernatorPool = NewGubernatorPool(&conf, conf.PoolWorkers, 0)
	s.global = newGlobalManager(conf.Behaviors, &s)
	s.mutliRegion = newMultiRegionManager(conf.Behaviors, &s)

	// Register our instance with all GRPC servers
	for _, srv := range conf.GRPCServers {
		RegisterV1Server(srv, &s)
		RegisterPeersV1Server(srv, &s)
	}

	if s.conf.Loader == nil {
		return &s, nil
	}

	// Load the cache.
	err := s.gubernatorPool.Load(ctx)
	if err != nil {
		return nil, errors.Wrap(err, "Error in checkHandlerPool.Load")
	}

	return &s, nil
}

func (s *V1Instance) Close() (reterr error) {
	ctx := tracing.StartScope(context.Background())
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()

	if s.isClosed {
		return nil
	}

	if s.conf.Loader == nil {
		return nil
	}

	s.global.Close()
	s.mutliRegion.Close()

	err := s.gubernatorPool.Store(ctx)
	if err != nil {
		logrus.WithContext(ctx).
			WithError(err).
			Error("Error in checkHandlerPool.Store")
		return errors.Wrap(err, "Error in checkHandlerPool.Store")
	}

	err = s.gubernatorPool.Close()
	if err != nil {
		logrus.WithContext(ctx).
			WithError(err).
			Error("Error in checkHandlerPool.Close")
		return errors.Wrap(err, "Error in checkHandlerPool.Close")
	}

	s.isClosed = true
	return nil
}

// GetRateLimits is the public interface used by clients to request rate limits from the system. If the
// rate limit `Name` and `UniqueKey` is not owned by this instance then we forward the request to the
// peer that does.
func (s *V1Instance) GetRateLimits(ctx context.Context, r *GetRateLimitsReq) (retval *GetRateLimitsResp, reterr error) {
	ctx = tracing.StartScope(ctx)
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()
	span := trace.SpanFromContext(ctx)

	funcTimer := prometheus.NewTimer(funcTimeMetric.WithLabelValues("V1Instance.GetRateLimits"))
	defer funcTimer.ObserveDuration()

	concurrentCounter := atomic.AddInt64(&s.getRateLimitsCounter, 1)
	defer atomic.AddInt64(&s.getRateLimitsCounter, -1)
	span.SetAttributes(attribute.Int64("concurrentCounter", concurrentCounter))
	concurrentChecksMetric.Observe(float64(concurrentCounter))

	if len(r.Requests) > maxBatchSize {
		checkErrorCounter.WithLabelValues("Request too large").Add(1)
		return nil, status.Errorf(codes.OutOfRange,
			"Requests.RateLimits list too large; max size is '%d'", maxBatchSize)
	}

	resp := GetRateLimitsResp{
		Responses: make([]*RateLimitResp, len(r.Requests)),
	}

	var wg sync.WaitGroup
	asyncCh := make(chan AsyncResp, len(r.Requests))

	// For each item in the request body
	for i, req := range r.Requests {
		_ = tracing.NamedScope(ctx, "Iterate requests", func(ctx context.Context) error {
			key := req.Name + "_" + req.UniqueKey
			var peer *PeerClient
			var err error

			if len(req.UniqueKey) == 0 {
				checkErrorCounter.WithLabelValues("Invalid request").Add(1)
				resp.Responses[i] = &RateLimitResp{Error: "field 'unique_key' cannot be empty"}
				return nil
			}

			if len(req.Name) == 0 {
				checkErrorCounter.WithLabelValues("Invalid request").Add(1)
				resp.Responses[i] = &RateLimitResp{Error: "field 'namespace' cannot be empty"}
				return nil
			}

			if ctx.Err() != nil {
				err = errors.Wrap(ctx.Err(), "Error while iterating request items")
				span.RecordError(err)
				resp.Responses[i] = &RateLimitResp{
					Error: err.Error(),
				}
				return nil
			}

			peer, err = s.GetPeer(ctx, key)
			if err != nil {
				countError(err, "Error in GetPeer")
				err = errors.Wrapf(err, "Error in GetPeer, looking up peer that owns rate limit '%s'", key)
				resp.Responses[i] = &RateLimitResp{
					Error: err.Error(),
				}
				return nil
			}

			// If our server instance is the owner of this rate limit
			if peer.Info().IsOwner {
				// Apply our rate limit algorithm to the request
				getRateLimitCounter.WithLabelValues("local").Add(1)
				funcTimer1 := prometheus.NewTimer(funcTimeMetric.WithLabelValues("V1Instance.getRateLimit (local)"))
				resp.Responses[i], err = s.getRateLimit(ctx, req)
				funcTimer1.ObserveDuration()
				if err != nil {
					err = errors.Wrapf(err, "Error while apply rate limit for '%s'", key)
					span.RecordError(err)
					resp.Responses[i] = &RateLimitResp{Error: err.Error()}
				}
			} else {
				if HasBehavior(req.Behavior, Behavior_GLOBAL) {
					resp.Responses[i], err = s.getGlobalRateLimit(ctx, req)
					if err != nil {
						err = errors.Wrap(err, "Error in getGlobalRateLimit")
						span.RecordError(err)
						resp.Responses[i] = &RateLimitResp{Error: err.Error()}
					}

					// Inform the client of the owner key of the key
					resp.Responses[i].Metadata = map[string]string{"owner": peer.Info().GRPCAddress}
					return nil
				}

				// Request must be forwarded to peer that owns the key.
				// Launch remote peer request in goroutine.
				wg.Add(1)
				go s.asyncRequests(ctx, &AsyncReq{
					AsyncCh: asyncCh,
					Peer:    peer,
					Req:     req,
					WG:      &wg,
					Key:     key,
					Idx:     i,
				})
			}

			return nil
		})
	}

	// Wait for any async responses if any
	ctxWait := tracing.StartNamedScope(ctx, "Wait for responses")
	wg.Wait()
	tracing.EndScope(ctxWait, nil)

	close(asyncCh)
	for a := range asyncCh {
		resp.Responses[a.Idx] = a.Resp
	}

	return &resp, nil
}

type AsyncResp struct {
	Idx  int
	Resp *RateLimitResp
}

type AsyncReq struct {
	WG      *sync.WaitGroup
	AsyncCh chan AsyncResp
	Req     *RateLimitReq
	Peer    *PeerClient
	Key     string
	Idx     int
}

func (s *V1Instance) asyncRequests(ctx context.Context, req *AsyncReq) {
	var attempts int
	var err error

	ctx = tracing.StartScope(ctx)
	defer tracing.EndScope(ctx, nil)
	span := trace.SpanFromContext(ctx)
	span.SetAttributes(
		attribute.String("request.name", req.Req.Name),
		attribute.String("request.key", req.Req.UniqueKey),
		attribute.Int64("request.limit", req.Req.Limit),
		attribute.Int64("request.duration", req.Req.Duration),
		attribute.String("peer.grpcAddress", req.Peer.Info().GRPCAddress),
	)

	funcTimer := prometheus.NewTimer(funcTimeMetric.WithLabelValues("V1Instance.asyncRequests"))
	defer funcTimer.ObserveDuration()

	resp := AsyncResp{
		Idx: req.Idx,
	}

	for {
		if attempts > 5 {
			logrus.WithContext(ctx).
				WithError(err).
				WithField("key", req.Key).
				Error("GetPeer() returned peer that is not connected")
			countError(err, "Peer not connected")
			err = errors.Wrapf(err, "GetPeer() keeps returning peers that are not connected for '%s'", req.Key)
			resp.Resp = &RateLimitResp{Error: err.Error()}
			break
		}

		// If we are attempting again, the owner of the this rate limit might have changed to us!
		if attempts != 0 {
			if req.Peer.Info().IsOwner {
				getRateLimitCounter.WithLabelValues("local").Add(1)
				resp.Resp, err = s.getRateLimit(ctx, req.Req)
				if err != nil {
					logrus.WithContext(ctx).
						WithError(err).
						WithField("key", req.Key).
						Error("Error applying rate limit")
					err = errors.Wrapf(err, "Error in getRateLimit for '%s'", req.Key)
					resp.Resp = &RateLimitResp{Error: err.Error()}
				}
				break
			}
		}

		// Make an RPC call to the peer that owns this rate limit
		getRateLimitCounter.WithLabelValues("forward").Add(1)
		r, err := req.Peer.GetPeerRateLimit(ctx, req.Req)
		if err != nil {
			if IsNotReady(err) {
				attempts++
				asyncRequestRetriesCounter.WithLabelValues(req.Req.Name).Add(1)
				req.Peer, err = s.GetPeer(ctx, req.Key)
				if err != nil {
					errPart := fmt.Sprintf("Error finding peer that owns rate limit '%s'", req.Key)
					logrus.WithContext(ctx).
						WithError(err).
						WithField("key", req.Key).
						Error(errPart)
					countError(err, "Error in GetPeer")
					err = errors.Wrap(err, errPart)
					resp.Resp = &RateLimitResp{Error: err.Error()}
					break
				}
				continue
			}

			logrus.WithContext(ctx).
				WithError(err).
				WithField("key", req.Key).
				Error("Error fetching rate limit from peer")
			// Not calling `countError()` because we expect the remote end to
			// report this error.
			err = errors.Wrap(err, fmt.Sprintf("Error while fetching rate limit '%s' from peer", req.Key))
			resp.Resp = &RateLimitResp{Error: err.Error()}
			break
		}

		// Inform the client of the owner key of the key
		resp.Resp = r
		resp.Resp.Metadata = map[string]string{"owner": req.Peer.Info().GRPCAddress}
		break
	}

	req.AsyncCh <- resp
	req.WG.Done()

	if isDeadlineExceeded(ctx.Err()) {
		checkErrorCounter.WithLabelValues("Timeout forwarding to peer").Add(1)
	}
}

// getGlobalRateLimit handles rate limits that are marked as `Behavior = GLOBAL`. Rate limit responses
// are returned from the local cache and the hits are queued to be sent to the owning peer.
func (s *V1Instance) getGlobalRateLimit(ctx context.Context, req *RateLimitReq) (retval *RateLimitResp, reterr error) {
	ctx = tracing.StartScope(ctx)
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()

	funcTimer := prometheus.NewTimer(funcTimeMetric.WithLabelValues("V1Instance.getGlobalRateLimit"))
	defer funcTimer.ObserveDuration()
	// Queue the hit for async update after we have prepared our response.
	// NOTE: The defer here avoids a race condition where we queue the req to
	// be forwarded to the owning peer in a separate goroutine but simultaneously
	// access and possibly copy the req in this method.
	defer s.global.QueueHit(req)

	item, ok, err := s.gubernatorPool.GetCacheItem(ctx, req.HashKey())
	if err != nil {
		countError(err, "Error in gubernatorPool.GetCacheItem")
		return nil, errors.Wrap(err, "Error in checkHandlerPool.GetCacheItem")
	}
	if ok {
		// Global rate limits are always stored as RateLimitResp regardless of algorithm
		rl, ok := item.Value.(*RateLimitResp)
		if ok {
			return rl, nil
		}
		// We get here if the owning node hasn't asynchronously forwarded it's updates to us yet and
		// our cache still holds the rate limit we created on the first hit.
	}

	cpy := proto.Clone(req).(*RateLimitReq)
	cpy.Behavior = Behavior_NO_BATCHING

	// Process the rate limit like we own it
	getRateLimitCounter.WithLabelValues("global").Add(1)
	resp, err := s.getRateLimit(ctx, cpy)
	if err != nil {
		return nil, errors.Wrap(err, "Error in getRateLimit")
	}

	return resp, nil
}

// UpdatePeerGlobals updates the local cache with a list of global rate limits. This method should only
// be called by a peer who is the owner of a global rate limit.
func (s *V1Instance) UpdatePeerGlobals(ctx context.Context, r *UpdatePeerGlobalsReq) (retval *UpdatePeerGlobalsResp, reterr error) {
	ctx = tracing.StartScope(ctx)
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()

	for _, g := range r.Globals {
		item := &CacheItem{
			ExpireAt:  g.Status.ResetTime,
			Algorithm: g.Algorithm,
			Value:     g.Status,
			Key:       g.Key,
		}
		err := s.gubernatorPool.AddCacheItem(ctx, g.Key, item)
		if err != nil {
			return nil, errors.Wrap(err, "Error in checkHandlerPool.AddCacheItem")
		}
	}

	return &UpdatePeerGlobalsResp{}, nil
}

// GetPeerRateLimits is called by other peers to get the rate limits owned by this peer.
func (s *V1Instance) GetPeerRateLimits(ctx context.Context, r *GetPeerRateLimitsReq) (retval *GetPeerRateLimitsResp, reterr error) {
	ctx = tracing.StartScope(ctx)
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()
	span := trace.SpanFromContext(ctx)
	span.SetAttributes(attribute.Int("numRequests", len(r.Requests)))

	if len(r.Requests) > maxBatchSize {
		err := fmt.Errorf("'PeerRequest.rate_limits' list too large; max size is '%d'", maxBatchSize)
		checkErrorCounter.WithLabelValues("Request too large").Add(1)
		return nil, status.Error(codes.OutOfRange, err.Error())
	}

	// Invoke each rate limit request.
	type reqIn struct {
		idx int
		req *RateLimitReq
	}
	type respOut struct {
		idx int
		rl  *RateLimitResp
	}

	resp := &GetPeerRateLimitsResp{
		RateLimits: make([]*RateLimitResp, len(r.Requests)),
	}
	respChan := make(chan respOut)
	var respWg sync.WaitGroup
	respWg.Add(1)

	go func() {
		// Capture each response and keep in stable order.
		for out := range respChan {
			resp.RateLimits[out.idx] = out.rl
		}

		respWg.Done()
	}()

	// Fan out requests.
	concurrencyLimit := s.conf.PoolWorkers
	fan := syncutil.NewFanOut(concurrencyLimit)
	for idx, req := range r.Requests {
		fan.Run(func(in interface{}) error {
			rin := in.(reqIn)
			rl, err := s.getRateLimit(ctx, rin.req)
			if err != nil {
				// Return the error for this request
				err = errors.Wrap(err, "Error in getRateLimit")
				span.RecordError(err)
				rl = &RateLimitResp{Error: err.Error()}
				// checkErrorCounter is updated within getRateLimit().
			}

			respChan <- respOut{rin.idx, rl}
			return nil
		}, reqIn{idx, req})
	}

	// Wait for all requests to be handled, then clean up.
	_ = fan.Wait()
	close(respChan)
	respWg.Wait()

	return resp, nil
}

// HealthCheck Returns the health of our instance.
func (s *V1Instance) HealthCheck(ctx context.Context, r *HealthCheckReq) (retval *HealthCheckResp, reterr error) {
	ctx = tracing.StartScope(ctx)
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()
	span := trace.SpanFromContext(ctx)

	var errs []string

	s.peerMutex.RLock()
	defer s.peerMutex.RUnlock()
	span.AddEvent("peerMutex.RLock()")

	// Iterate through local peers and get their last errors
	localPeers := s.conf.LocalPicker.Peers()
	for _, peer := range localPeers {
		lastErr := peer.GetLastErr()

		if lastErr != nil {
			for _, errMsg := range lastErr {
				err := fmt.Errorf("Error returned from local peer.GetLastErr: %s", errMsg)
				span.RecordError(err)
				errs = append(errs, err.Error())
			}
		}
	}

	// Do the same for region peers
	regionPeers := s.conf.RegionPicker.Peers()
	for _, peer := range regionPeers {
		lastErr := peer.GetLastErr()

		if lastErr != nil {
			for _, errMsg := range lastErr {
				err := fmt.Errorf("Error returned from region peer.GetLastErr: %s", errMsg)
				span.RecordError(err)
				errs = append(errs, err.Error())
			}
		}
	}

	health := HealthCheckResp{
		PeerCount: int32(len(localPeers) + len(regionPeers)),
		Status:    Healthy,
	}

	if len(errs) != 0 {
		health.Status = UnHealthy
		health.Message = strings.Join(errs, "|")
	}

	span.SetAttributes(
		attribute.Int64("health.peerCount", int64(health.PeerCount)),
		attribute.String("health.status", health.Status),
	)

	return &health, nil
}

func (s *V1Instance) getRateLimit(ctx context.Context, r *RateLimitReq) (retval *RateLimitResp, reterr error) {
	ctx = tracing.StartScope(ctx)
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()
	span := trace.SpanFromContext(ctx)
	span.SetAttributes(
		attribute.String("request.name", r.Name),
		attribute.String("request.key", r.UniqueKey),
		attribute.Int64("request.limit", r.Limit),
		attribute.Int64("request.duration", r.Duration),
	)

	funcTimer := prometheus.NewTimer(funcTimeMetric.WithLabelValues("V1Instance.getRateLimit"))
	defer funcTimer.ObserveDuration()
	checkCounter.Add(1)

	if HasBehavior(r.Behavior, Behavior_GLOBAL) {
		s.global.QueueUpdate(r)
		span.AddEvent("s.global.QueueUpdate(r)")
	}

	if HasBehavior(r.Behavior, Behavior_MULTI_REGION) {
		s.mutliRegion.QueueHits(r)
		span.AddEvent("s.mutliRegion.QueueHits(r)")
	}

	resp, err := s.gubernatorPool.GetRateLimit(ctx, r)
	if isDeadlineExceeded(err) {
		checkErrorCounter.WithLabelValues("Timeout").Add(1)
	}

	return resp, err
}

// SetPeers is called by the implementor to indicate the pool of peers has changed
func (s *V1Instance) SetPeers(peerInfo []PeerInfo) {
	localPicker := s.conf.LocalPicker.New()
	regionPicker := s.conf.RegionPicker.New()

	for _, info := range peerInfo {
		// Add peers that are not in our local DC to the RegionPicker
		if info.DataCenter != s.conf.DataCenter {
			peer := s.conf.RegionPicker.GetByPeerInfo(info)
			// If we don't have an existing PeerClient create a new one
			if peer == nil {
				peer = NewPeerClient(PeerConfig{
					TLS:      s.conf.PeerTLS,
					Behavior: s.conf.Behaviors,
					Info:     info,
				})
			}
			regionPicker.Add(peer)
			continue
		}
		// If we don't have an existing PeerClient create a new one
		peer := s.conf.LocalPicker.GetByPeerInfo(info)
		if peer == nil {
			peer = NewPeerClient(PeerConfig{
				TLS:      s.conf.PeerTLS,
				Behavior: s.conf.Behaviors,
				Info:     info,
			})
		}
		localPicker.Add(peer)
	}

	s.peerMutex.Lock()

	// Replace our current pickers
	oldLocalPicker := s.conf.LocalPicker
	oldRegionPicker := s.conf.RegionPicker
	s.conf.LocalPicker = localPicker
	s.conf.RegionPicker = regionPicker
	s.peerMutex.Unlock()

	s.log.WithField("peers", peerInfo).Debug("peers updated")

	// Shutdown any old peers we no longer need
	ctx, cancel := ctxutil.WithTimeout(context.Background(), s.conf.Behaviors.BatchTimeout)
	defer cancel()

	var shutdownPeers []*PeerClient
	for _, peer := range oldLocalPicker.Peers() {
		if peerInfo := s.conf.LocalPicker.GetByPeerInfo(peer.Info()); peerInfo == nil {
			shutdownPeers = append(shutdownPeers, peer)
		}
	}

	for _, regionPicker := range oldRegionPicker.Pickers() {
		for _, peer := range regionPicker.Peers() {
			if peerInfo := s.conf.RegionPicker.GetByPeerInfo(peer.Info()); peerInfo == nil {
				shutdownPeers = append(shutdownPeers, peer)
			}
		}
	}

	var wg syncutil.WaitGroup
	for _, p := range shutdownPeers {
		wg.Run(func(obj interface{}) error {
			pc := obj.(*PeerClient)
			err := pc.Shutdown(ctx)
			if err != nil {
				s.log.WithError(err).WithField("peer", pc).Error("while shutting down peer")
			}
			return nil
		}, p)
	}
	wg.Wait()

	if len(shutdownPeers) > 0 {
		var peers []string
		for _, p := range shutdownPeers {
			peers = append(peers, p.Info().GRPCAddress)
		}
		s.log.WithField("peers", peers).Debug("peers shutdown")
	}
}

// GetPeer returns a peer client for the hash key provided
func (s *V1Instance) GetPeer(ctx context.Context, key string) (retval *PeerClient, reterr error) {
	ctx = tracing.StartScope(ctx)
	defer func() {
		tracing.EndScope(ctx, reterr)
	}()
	span := trace.SpanFromContext(ctx)

	funcTimer := prometheus.NewTimer(funcTimeMetric.WithLabelValues("V1Instance.GetPeer"))
	defer funcTimer.ObserveDuration()
	lockTimer := prometheus.NewTimer(funcTimeMetric.WithLabelValues("V1Instance.GetPeer_RLock"))

	s.peerMutex.RLock()
	defer s.peerMutex.RUnlock()
	span.AddEvent("peerMutex.RLock()")
	lockTimer.ObserveDuration()

	peer, err := s.conf.LocalPicker.Get(key)
	if err != nil {
		return nil, errors.Wrap(err, "Error in conf.LocalPicker.Get")
	}

	return peer, nil
}

func (s *V1Instance) GetPeerList() []*PeerClient {
	s.peerMutex.RLock()
	defer s.peerMutex.RUnlock()
	return s.conf.LocalPicker.Peers()
}

func (s *V1Instance) GetRegionPickers() map[string]PeerPicker {
	s.peerMutex.RLock()
	defer s.peerMutex.RUnlock()
	return s.conf.RegionPicker.Pickers()
}

// Describe fetches prometheus metrics to be registered
func (s *V1Instance) Describe(ch chan<- *prometheus.Desc) {
	ch <- s.global.asyncMetrics.Desc()
	ch <- s.global.broadcastMetrics.Desc()
	getRateLimitCounter.Describe(ch)
	funcTimeMetric.Describe(ch)
	asyncRequestRetriesCounter.Describe(ch)
	queueLengthMetric.Describe(ch)
	concurrentChecksMetric.Describe(ch)
	checkErrorCounter.Describe(ch)
	overLimitCounter.Describe(ch)
	checkCounter.Describe(ch)
	poolWorkerQueueLength.Describe(ch)
	batchSendDurationMetric.Describe(ch)
}

// Collect fetches metrics from the server for use by prometheus
func (s *V1Instance) Collect(ch chan<- prometheus.Metric) {
	ch <- s.global.asyncMetrics
	ch <- s.global.broadcastMetrics
	getRateLimitCounter.Collect(ch)
	funcTimeMetric.Collect(ch)
	asyncRequestRetriesCounter.Collect(ch)
	queueLengthMetric.Collect(ch)
	concurrentChecksMetric.Collect(ch)
	checkErrorCounter.Collect(ch)
	overLimitCounter.Collect(ch)
	checkCounter.Collect(ch)
	poolWorkerQueueLength.Collect(ch)
	batchSendDurationMetric.Collect(ch)
}

// HasBehavior returns true if the provided behavior is set
func HasBehavior(b Behavior, flag Behavior) bool {
	return b&flag != 0
}

// SetBehavior sets or clears the behavior depending on the boolean `set`
func SetBehavior(b *Behavior, flag Behavior, set bool) {
	if set {
		*b = *b | flag
	} else {
		mask := *b ^ flag
		*b &= mask
	}
}

// Count an error type in the checkErrorCounter metric.
// Recurse into wrapped errors if necessary.
func countError(err error, defaultType string) {
	for {
		if err == nil {
			checkErrorCounter.WithLabelValues(defaultType).Add(1)
			return
		}
		if errors.Is(err, context.DeadlineExceeded) {
			checkErrorCounter.WithLabelValues("Timeout").Add(1)
			return
		}

		err = errors.Unwrap(err)
	}
}

func isDeadlineExceeded(err error) bool {
	for {
		if err == nil {
			return false
		}
		if errors.Is(err, context.DeadlineExceeded) {
			return true
		}

		err = errors.Unwrap(err)
	}
}