open-consul/agent/router/manager.go

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// Package servers provides a Manager interface for Manager managed
// metadata.Server objects. The servers package manages servers from a Consul
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// client's perspective (i.e. a list of servers that a client talks with for
// RPCs). The servers package does not provide any API guarantees and should
// be called only by `hashicorp/consul`.
package router
import (
"math/rand"
"net"
"sync"
"sync/atomic"
"time"
"github.com/hashicorp/consul/agent/metadata"
"github.com/hashicorp/consul/lib"
"github.com/hashicorp/consul/logging"
"github.com/hashicorp/go-hclog"
)
const (
// clientRPCJitterFraction determines the amount of jitter added to
// clientRPCMinReuseDuration before a connection is expired and a new
// connection is established in order to rebalance load across consul
// servers. The cluster-wide number of connections per second from
// rebalancing is applied after this jitter to ensure the CPU impact
// is always finite. See newRebalanceConnsPerSecPerServer's comment
// for additional commentary.
//
// For example, in a 10K consul cluster with 5x servers, this default
// averages out to ~13 new connections from rebalancing per server
// per second (each connection is reused for 120s to 180s).
clientRPCJitterFraction = 2
// clientRPCMinReuseDuration controls the minimum amount of time RPC
// queries are sent over an established connection to a single server
clientRPCMinReuseDuration = 120 * time.Second
// Limit the number of new connections a server receives per second
// for connection rebalancing. This limit caps the load caused by
// continual rebalancing efforts when a cluster is in equilibrium. A
// lower value comes at the cost of increased recovery time after a
// partition. This parameter begins to take effect when there are
// more than ~48K clients querying 5x servers or at lower server
// values when there is a partition.
//
// For example, in a 100K consul cluster with 5x servers, it will
// take ~5min for all servers to rebalance their connections. If
// 99,995 agents are in the minority talking to only one server, it
// will take ~26min for all servers to rebalance. A 10K cluster in
// the same scenario will take ~2.6min to rebalance.
newRebalanceConnsPerSecPerServer = 64
)
// ManagerSerfCluster is an interface wrapper around Serf in order to make this
// easier to unit test.
type ManagerSerfCluster interface {
NumNodes() int
}
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// Pinger is an interface wrapping client.ConnPool to prevent a cyclic import
// dependency.
type Pinger interface {
Ping(dc, nodeName string, addr net.Addr, version int) (bool, error)
}
// serverList is a local copy of the struct used to maintain the list of
// Consul servers used by Manager.
//
// NOTE(sean@): We are explicitly relying on the fact that serverList will
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// be copied onto the stack. Please keep this structure light.
type serverList struct {
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// servers tracks the locally known servers. List membership is
// maintained by Serf.
servers []*metadata.Server
}
type Manager struct {
// listValue manages the atomic load/store of a Manager's serverList
listValue atomic.Value
listLock sync.Mutex
// rebalanceTimer controls the duration of the rebalance interval
rebalanceTimer *time.Timer
// shutdownCh is a copy of the channel in consul.Client
shutdownCh chan struct{}
logger hclog.Logger
// clusterInfo is used to estimate the approximate number of nodes in
// a cluster and limit the rate at which it rebalances server
// connections. ManagerSerfCluster is an interface that wraps serf.
clusterInfo ManagerSerfCluster
// connPoolPinger is used to test the health of a server in the
// connection pool. Pinger is an interface that wraps
// client.ConnPool.
connPoolPinger Pinger
// serverName has the name of the managers's server. This is used to
// short-circuit pinging to itself.
serverName string
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// notifyFailedBarrier is acts as a barrier to prevent queuing behind
// serverListLog and acts as a TryLock().
notifyFailedBarrier int32
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// offline is used to indicate that there are no servers, or that all
// known servers have failed the ping test.
offline int32
}
// AddServer takes out an internal write lock and adds a new server. If the
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// server is not known, appends the server to the list. The new server will
// begin seeing use after the rebalance timer fires or enough servers fail
// organically. If the server is already known, merge the new server
// details.
func (m *Manager) AddServer(s *metadata.Server) {
m.listLock.Lock()
defer m.listLock.Unlock()
l := m.getServerList()
// Check if this server is known
found := false
for idx, existing := range l.servers {
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if existing.Name == s.Name {
newServers := make([]*metadata.Server, len(l.servers))
copy(newServers, l.servers)
// Overwrite the existing server details in order to
// possibly update metadata (e.g. server version)
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newServers[idx] = s
l.servers = newServers
found = true
break
}
}
// Add to the list if not known
if !found {
newServers := make([]*metadata.Server, len(l.servers), len(l.servers)+1)
copy(newServers, l.servers)
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newServers = append(newServers, s)
l.servers = newServers
}
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// Assume we are no longer offline since we've just seen a new server.
atomic.StoreInt32(&m.offline, 0)
// Start using this list of servers.
m.saveServerList(l)
}
// UpdateTLS updates the TLS setting for the servers in this manager
func (m *Manager) UpdateTLS(useTLS bool) {
m.listLock.Lock()
defer m.listLock.Unlock()
list := m.getServerList()
for _, server := range list.servers {
server.UseTLS = useTLS
}
m.saveServerList(list)
}
// cycleServers returns a new list of servers that has dequeued the first
// server and enqueued it at the end of the list. cycleServers assumes the
// caller is holding the listLock. cycleServer does not test or ping
// the next server inline. cycleServer may be called when the environment
// has just entered an unhealthy situation and blocking on a server test is
// less desirable than just returning the next server in the firing line. If
// the next server fails, it will fail fast enough and cycleServer will be
// called again.
func (l *serverList) cycleServer() (servers []*metadata.Server) {
numServers := len(l.servers)
if numServers < 2 {
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return servers // No action required
}
newServers := make([]*metadata.Server, 0, numServers)
newServers = append(newServers, l.servers[1:]...)
newServers = append(newServers, l.servers[0])
return newServers
}
// removeServerByKey performs an inline removal of the first matching server
func (l *serverList) removeServerByKey(targetKey *metadata.Key) {
for i, s := range l.servers {
if targetKey.Equal(s.Key()) {
copy(l.servers[i:], l.servers[i+1:])
l.servers[len(l.servers)-1] = nil
l.servers = l.servers[:len(l.servers)-1]
return
}
}
}
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// shuffleServers shuffles the server list in place
func (l *serverList) shuffleServers() {
for i := len(l.servers) - 1; i > 0; i-- {
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j := rand.Int31n(int32(i + 1))
l.servers[i], l.servers[j] = l.servers[j], l.servers[i]
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}
}
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// IsOffline checks to see if all the known servers have failed their ping
// test during the last rebalance.
func (m *Manager) IsOffline() bool {
offline := atomic.LoadInt32(&m.offline)
return offline == 1
}
// FindServer takes out an internal "read lock" and searches through the list
// of servers to find a "healthy" server. If the server is actually
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// unhealthy, we rely on Serf to detect this and remove the node from the
// server list. If the server at the front of the list has failed or fails
// during an RPC call, it is rotated to the end of the list. If there are no
// servers available, return nil.
func (m *Manager) FindServer() *metadata.Server {
l := m.getServerList()
numServers := len(l.servers)
if numServers == 0 {
m.logger.Warn("No servers available")
return nil
}
// Return whatever is at the front of the list because it is
// assumed to be the oldest in the server list (unless -
// hypothetically - the server list was rotated right after a
// server was added).
return l.servers[0]
}
func (m *Manager) checkServers(fn func(srv *metadata.Server) bool) bool {
for _, srv := range m.getServerList().servers {
if !fn(srv) {
return false
}
}
return true
}
func (m *Manager) CheckServers(fn func(srv *metadata.Server) bool) {
_ = m.checkServers(fn)
}
// getServerList is a convenience method which hides the locking semantics
// of atomic.Value from the caller.
func (m *Manager) getServerList() serverList {
return m.listValue.Load().(serverList)
}
// saveServerList is a convenience method which hides the locking semantics
// of atomic.Value from the caller.
func (m *Manager) saveServerList(l serverList) {
m.listValue.Store(l)
}
// New is the only way to safely create a new Manager struct.
func New(logger hclog.Logger, shutdownCh chan struct{}, clusterInfo ManagerSerfCluster, connPoolPinger Pinger, serverName string) (m *Manager) {
if logger == nil {
logger = hclog.New(&hclog.LoggerOptions{})
}
m = new(Manager)
m.logger = logger.Named(logging.Manager)
m.clusterInfo = clusterInfo // can't pass *consul.Client: import cycle
m.connPoolPinger = connPoolPinger // can't pass *consul.ConnPool: import cycle
m.rebalanceTimer = time.NewTimer(clientRPCMinReuseDuration)
m.shutdownCh = shutdownCh
m.serverName = serverName
atomic.StoreInt32(&m.offline, 1)
l := serverList{}
l.servers = make([]*metadata.Server, 0)
m.saveServerList(l)
return m
}
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// NotifyFailedServer marks the passed in server as "failed" by rotating it
// to the end of the server list.
func (m *Manager) NotifyFailedServer(s *metadata.Server) {
l := m.getServerList()
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// If the server being failed is not the first server on the list,
// this is a noop. If, however, the server is failed and first on
// the list, acquire the lock, retest, and take the penalty of moving
// the server to the end of the list.
// Only rotate the server list when there is more than one server
if len(l.servers) > 1 && l.servers[0].Name == s.Name &&
// Use atomic.CAS to emulate a TryLock().
atomic.CompareAndSwapInt32(&m.notifyFailedBarrier, 0, 1) {
defer atomic.StoreInt32(&m.notifyFailedBarrier, 0)
// Grab a lock, retest, and take the hit of cycling the first
// server to the end.
m.listLock.Lock()
defer m.listLock.Unlock()
l = m.getServerList()
if len(l.servers) > 1 && l.servers[0].Name == s.Name {
l.servers = l.cycleServer()
m.saveServerList(l)
m.logger.Debug("cycled away from server", "server", s.String())
}
}
}
// NumServers takes out an internal "read lock" and returns the number of
// servers. numServers includes both healthy and unhealthy servers.
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func (m *Manager) NumServers() int {
l := m.getServerList()
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return len(l.servers)
}
// RebalanceServers shuffles the list of servers on this metadata. The server
// at the front of the list is selected for the next RPC. RPC calls that
// fail for a particular server are rotated to the end of the list. This
// method reshuffles the list periodically in order to redistribute work
// across all known consul servers (i.e. guarantee that the order of servers
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// in the server list is not positively correlated with the age of a server
// in the Consul cluster). Periodically shuffling the server list prevents
// long-lived clients from fixating on long-lived servers.
//
// Unhealthy servers are removed when serf notices the server has been
// deregistered. Before the newly shuffled server list is saved, the new
// remote endpoint is tested to ensure its responsive.
func (m *Manager) RebalanceServers() {
// Obtain a copy of the current serverList
l := m.getServerList()
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// Shuffle servers so we have a chance of picking a new one.
l.shuffleServers()
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// Iterate through the shuffled server list to find an assumed
// healthy server. NOTE: Do not iterate on the list directly because
// this loop mutates the server list in-place.
var foundHealthyServer bool
for i := 0; i < len(l.servers); i++ {
// Always test the first server. Failed servers are cycled
// while Serf detects the node has failed.
srv := l.servers[0]
// check to see if the manager is trying to ping itself,
// continue if that is the case.
if m.serverName != "" && srv.Name == m.serverName {
continue
}
ok, err := m.connPoolPinger.Ping(srv.Datacenter, srv.ShortName, srv.Addr, srv.Version)
if ok {
foundHealthyServer = true
break
}
m.logger.Debug("pinging server failed",
"server", srv.String(),
"error", err,
)
l.servers = l.cycleServer()
}
// If no healthy servers were found, sleep and wait for Serf to make
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// the world a happy place again. Update the offline status.
if foundHealthyServer {
atomic.StoreInt32(&m.offline, 0)
} else {
atomic.StoreInt32(&m.offline, 1)
m.logger.Debug("No healthy servers during rebalance, aborting")
return
}
// Verify that all servers are present
if m.reconcileServerList(&l) {
m.logger.Debug("Rebalanced servers, new active server",
"number_of_servers", len(l.servers),
"active_server", l.servers[0].String(),
)
}
// else {
// reconcileServerList failed because Serf removed the server
// that was at the front of the list that had successfully
// been Ping'ed. Between the Ping and reconcile, a Serf
// event had shown up removing the node.
//
// Instead of doing any heroics, "freeze in place" and
// continue to use the existing connection until the next
// rebalance occurs.
// }
}
// reconcileServerList returns true when the first server in serverList
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// exists in the receiver's serverList. If true, the merged serverList is
// stored as the receiver's serverList. Returns false if the first server
// does not exist in the list (i.e. was removed by Serf during a
// PingConsulServer() call. Newly added servers are appended to the list and
// other missing servers are removed from the list.
func (m *Manager) reconcileServerList(l *serverList) bool {
m.listLock.Lock()
defer m.listLock.Unlock()
// newServerCfg is a serverList that has been kept up to date with
// Serf node join and node leave events.
newServerCfg := m.getServerList()
// If Serf has removed all nodes, or there is no selected server
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// (zero nodes in serverList), abort early.
if len(newServerCfg.servers) == 0 || len(l.servers) == 0 {
return false
}
type targetServer struct {
server *metadata.Server
// 'b' == both
// 'o' == original
// 'n' == new
state byte
}
mergedList := make(map[metadata.Key]*targetServer, len(l.servers))
for _, s := range l.servers {
mergedList[*s.Key()] = &targetServer{server: s, state: 'o'}
}
for _, s := range newServerCfg.servers {
k := s.Key()
_, found := mergedList[*k]
if found {
mergedList[*k].state = 'b'
} else {
mergedList[*k] = &targetServer{server: s, state: 'n'}
}
}
// Ensure the selected server has not been removed by Serf
selectedServerKey := l.servers[0].Key()
if v, found := mergedList[*selectedServerKey]; found && v.state == 'o' {
return false
}
// Append any new servers and remove any old servers
for k, v := range mergedList {
switch v.state {
case 'b':
// Do nothing, server exists in both
case 'o':
// Server has been removed
l.removeServerByKey(&k)
case 'n':
// Server added
l.servers = append(l.servers, v.server)
default:
panic("unknown merge list state")
}
}
m.saveServerList(*l)
return true
}
// RemoveServer takes out an internal write lock and removes a server from
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// the server list.
func (m *Manager) RemoveServer(s *metadata.Server) {
m.listLock.Lock()
defer m.listLock.Unlock()
l := m.getServerList()
// Remove the server if known
for i := range l.servers {
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if l.servers[i].Name == s.Name {
newServers := make([]*metadata.Server, 0, len(l.servers)-1)
newServers = append(newServers, l.servers[:i]...)
newServers = append(newServers, l.servers[i+1:]...)
l.servers = newServers
m.saveServerList(l)
return
}
}
}
// refreshServerRebalanceTimer is only called once m.rebalanceTimer expires.
func (m *Manager) refreshServerRebalanceTimer() time.Duration {
l := m.getServerList()
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numServers := len(l.servers)
// Limit this connection's life based on the size (and health) of the
// cluster. Never rebalance a connection more frequently than
// connReuseLowWatermarkDuration, and make sure we never exceed
// clusterWideRebalanceConnsPerSec operations/s across numLANMembers.
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clusterWideRebalanceConnsPerSec := float64(numServers * newRebalanceConnsPerSecPerServer)
connReuseLowWatermarkDuration := clientRPCMinReuseDuration + lib.RandomStagger(clientRPCMinReuseDuration/clientRPCJitterFraction)
numLANMembers := m.clusterInfo.NumNodes()
connRebalanceTimeout := lib.RateScaledInterval(clusterWideRebalanceConnsPerSec, connReuseLowWatermarkDuration, numLANMembers)
m.rebalanceTimer.Reset(connRebalanceTimeout)
return connRebalanceTimeout
}
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// ResetRebalanceTimer resets the rebalance timer. This method exists for
// testing and should not be used directly.
func (m *Manager) ResetRebalanceTimer() {
m.listLock.Lock()
defer m.listLock.Unlock()
m.rebalanceTimer.Reset(clientRPCMinReuseDuration)
}
// Start is used to start and manage the task of automatically shuffling and
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// rebalancing the list of Consul servers. This maintenance only happens
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// periodically based on the expiration of the timer. Failed servers are
// automatically cycled to the end of the list. New servers are appended to
// the list. The order of the server list must be shuffled periodically to
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// distribute load across all known and available Consul servers.
func (m *Manager) Start() {
for {
select {
case <-m.rebalanceTimer.C:
m.RebalanceServers()
m.refreshServerRebalanceTimer()
case <-m.shutdownCh:
m.logger.Info("shutting down")
return
}
}
}