2016-02-20 01:32:16 +00:00
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package server_manager
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import (
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"log"
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"math/rand"
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"sync"
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"sync/atomic"
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"time"
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"github.com/hashicorp/consul/consul/server_details"
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"github.com/hashicorp/consul/lib"
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)
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type consulServerEventTypes int
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const (
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// consulServersNodeJoin is used to notify of a new consulServer.
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// The primary effect of this is a reshuffling of consulServers and
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// finding a new preferredServer.
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consulServersNodeJoin = iota
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// consulServersRebalance is used to signal we should rebalance our
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// connection load across servers
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consulServersRebalance
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// consulServersRPCError is used to signal when a server has either
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// timed out or returned an error and we would like to have the
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// server manager find a new preferredServer.
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consulServersRPCError
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)
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const (
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// clientRPCJitterFraction determines the amount of jitter added to
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// clientRPCMinReuseDuration before a connection is expired and a new
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// connection is established in order to rebalance load across consul
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// servers. The cluster-wide number of connections per second from
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// rebalancing is applied after this jitter to ensure the CPU impact
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// is always finite. See newRebalanceConnsPerSecPerServer's comment
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// for additional commentary.
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//
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// For example, in a 10K consul cluster with 5x servers, this default
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// averages out to ~13 new connections from rebalancing per server
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// per second (each connection is reused for 120s to 180s).
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clientRPCJitterFraction = 2
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// clientRPCMinReuseDuration controls the minimum amount of time RPC
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// queries are sent over an established connection to a single server
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clientRPCMinReuseDuration = 120 * time.Second
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// Limit the number of new connections a server receives per second
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// for connection rebalancing. This limit caps the load caused by
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// continual rebalancing efforts when a cluster is in equilibrium. A
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// lower value comes at the cost of increased recovery time after a
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// partition. This parameter begins to take effect when there are
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// more than ~48K clients querying 5x servers or at lower server
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// values when there is a partition.
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//
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// For example, in a 100K consul cluster with 5x servers, it will
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// take ~5min for all servers to rebalance their connections. If
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// 99,995 agents are in the minority talking to only one server, it
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// will take ~26min for all servers to rebalance. A 10K cluster in
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// the same scenario will take ~2.6min to rebalance.
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newRebalanceConnsPerSecPerServer = 64
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)
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// serverCfg is the thread-safe configuration structure that is used to
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// maintain the list of consul servers in Client.
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//
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// NOTE(sean@): We are explicitly relying on the fact that this is copied.
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// Please keep this structure light.
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type serverConfig struct {
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// servers tracks the locally known servers
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servers []*server_details.ServerDetails
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// Timer used to control rebalancing of servers
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rebalanceTimer *time.Timer
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}
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type ServerManager struct {
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// serverConfig provides the necessary load/store semantics to
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// serverConfig
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serverConfigValue atomic.Value
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serverConfigLock sync.Mutex
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// consulServersCh is used to receive events related to the
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// maintenance of the list of consulServers
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consulServersCh chan consulServerEventTypes
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// shutdownCh is a copy of the channel in consul.Client
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shutdownCh chan struct{}
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// Logger uses the provided LogOutput
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logger *log.Logger
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}
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2016-02-20 02:57:15 +00:00
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// AddServer takes out an internal write lock and adds a new server. If the
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// server is not known, it adds the new server and schedules a rebalance. If
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// it is known, we merge the new server details.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) AddServer(server *server_details.ServerDetails) {
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sm.serverConfigLock.Lock()
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defer sm.serverConfigLock.Unlock()
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2016-02-20 02:56:15 +00:00
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serverCfg := sm.getServerConfig()
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2016-02-20 01:32:16 +00:00
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// Check if this server is known
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found := false
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for idx, existing := range serverCfg.servers {
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if existing.Name == server.Name {
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// Overwrite the existing server parts in order to
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// possibly update metadata (i.e. server version)
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serverCfg.servers[idx] = server
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found = true
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break
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}
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}
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// Add to the list if not known
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if !found {
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newServers := make([]*server_details.ServerDetails, len(serverCfg.servers)+1)
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copy(newServers, serverCfg.servers)
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serverCfg.servers = newServers
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// Notify the server maintenance task of a new server
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sm.consulServersCh <- consulServersNodeJoin
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}
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sm.serverConfigValue.Store(serverCfg)
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}
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2016-02-20 02:57:15 +00:00
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// CycleFailedServers takes out an internal write lock and dequeues all
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// failed servers and re-enqueues them. This method does not reshuffle the
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// server list. Because this changed the order of servers, we push out the
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// time at which a rebalance occurs.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) CycleFailedServers() {
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sm.serverConfigLock.Lock()
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defer sm.serverConfigLock.Unlock()
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2016-02-20 02:56:15 +00:00
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serverCfg := sm.getServerConfig()
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2016-02-20 01:32:16 +00:00
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for i := range serverCfg.servers {
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failCount := atomic.LoadUint64(&(serverCfg.servers[i].Disabled))
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if failCount == 0 {
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break
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} else if failCount > 0 {
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serverCfg.servers = serverCfg.cycleServer()
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}
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}
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serverCfg.resetRebalanceTimer(sm)
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sm.serverConfigValue.Store(serverCfg)
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}
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2016-02-20 02:57:15 +00:00
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// cycleServers returns a new list of servers that has dequeued the first
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// server and enqueued it at the end of the list. cycleServers assumes the
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// caller is holding the serverConfigLock.
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2016-02-20 01:32:16 +00:00
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func (sc *serverConfig) cycleServer() (servers []*server_details.ServerDetails) {
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numServers := len(servers)
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if numServers < 2 {
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2016-02-20 02:58:49 +00:00
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// No action required
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2016-02-20 01:32:16 +00:00
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return servers
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}
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var dequeuedServer *server_details.ServerDetails
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2016-02-20 02:58:49 +00:00
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newServers := make([]*server_details.ServerDetails, len(servers)+1)
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2016-02-20 01:32:16 +00:00
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dequeuedServer, newServers = servers[0], servers[1:]
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servers = append(newServers, dequeuedServer)
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return servers
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}
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2016-02-20 02:57:15 +00:00
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// FindHealthyServer takes out an internal "read lock" and searches through
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// the list of servers to find a healthy server.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) FindHealthyServer() (server *server_details.ServerDetails) {
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serverCfg := sm.getServerConfig()
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numServers := len(serverCfg.servers)
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if numServers == 0 {
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sm.logger.Printf("[ERR] consul: No servers found in the server config")
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return nil
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}
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// Find the first non-failing server in the server list. If this is
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// not the first server a prior RPC call marked the first server as
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// failed and we're waiting for the server management task to reorder
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// a working server to the front of the list.
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for i := range serverCfg.servers {
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failCount := atomic.LoadUint64(&(serverCfg.servers[i].Disabled))
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if failCount == 0 {
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server = serverCfg.servers[i]
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break
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}
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}
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return server
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}
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2016-02-20 02:57:15 +00:00
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// GetNumServers takes out an internal "read lock" and returns the number of
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// servers. numServers includes both healthy and unhealthy servers.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) GetNumServers() (numServers int) {
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serverCfg := sm.getServerConfig()
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numServers = len(serverCfg.servers)
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return numServers
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}
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2016-02-20 02:58:49 +00:00
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// getServerConfig is a convenience method to hide the locking semantics of
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// atomic.Value from the caller.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) getServerConfig() serverConfig {
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return sm.serverConfigValue.Load().(serverConfig)
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}
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// NewServerManager is the only way to safely create a new ServerManager
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// struct.
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//
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2016-02-20 02:58:49 +00:00
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// NOTE(sean@): We can not pass in *consul.Client due to an import cycle
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2016-02-20 01:32:16 +00:00
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func NewServerManager(logger *log.Logger, shutdownCh chan struct{}) (sm *ServerManager) {
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sm = new(ServerManager)
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// Create the initial serverConfig
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serverCfg := serverConfig{}
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sm.logger = logger
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sm.shutdownCh = shutdownCh
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sm.serverConfigValue.Store(serverCfg)
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return sm
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}
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2016-02-20 02:57:15 +00:00
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// NotifyFailedServer is an exported convenience function that allows callers
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// to pass in a server that has failed an RPC request and mark it as failed.
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// This will initiate a background task that will optimize the failed server
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// to the end of the serer list. No locks are required here because we are
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// bypassing the serverConfig and sending a message to ServerManager's
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// channel.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) NotifyFailedServer(server *server_details.ServerDetails) {
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atomic.AddUint64(&server.Disabled, 1)
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sm.consulServersCh <- consulServersRPCError
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}
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2016-02-20 02:57:15 +00:00
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// RebalanceServers takes out an internal write lock and shuffles the list of
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// servers on this agent. This allows for a redistribution of work across
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// consul servers and provides a guarantee that the order list of
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// ServerDetails isn't actually ordered, therefore we can sequentially walk
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// the array to pick a server without all agents in the cluster dog piling on
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// a single node.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) RebalanceServers() {
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sm.serverConfigLock.Lock()
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defer sm.serverConfigLock.Unlock()
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2016-02-20 02:56:15 +00:00
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serverCfg := sm.getServerConfig()
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2016-02-20 01:32:16 +00:00
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// Shuffle the server list on server join. Servers are selected from
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// the head of the list and are moved to the end of the list on
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// failure.
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for i := len(serverCfg.servers) - 1; i > 0; i-- {
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j := rand.Int31n(int32(i + 1))
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serverCfg.servers[i], serverCfg.servers[j] = serverCfg.servers[j], serverCfg.servers[i]
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}
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serverCfg.resetRebalanceTimer(sm)
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sm.serverConfigValue.Store(serverCfg)
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}
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2016-02-20 02:57:15 +00:00
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// RemoveServer takes out an internal write lock and removes a server from
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// the server list. No rebalancing happens as a result of the removed server
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// because we do not want a network partition which separated a server from
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// this agent to cause an increase in work. Instead we rely on the internal
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// already existing semantics to handle failure detection after a server has
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// been removed.
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2016-02-20 01:32:16 +00:00
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func (sm *ServerManager) RemoveServer(server *server_details.ServerDetails) {
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sm.serverConfigLock.Lock()
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defer sm.serverConfigLock.Unlock()
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2016-02-20 02:56:15 +00:00
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serverCfg := sm.getServerConfig()
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2016-02-20 01:32:16 +00:00
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// Remove the server if known
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n := len(serverCfg.servers)
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for i := 0; i < n; i++ {
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if serverCfg.servers[i].Name == server.Name {
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serverCfg.servers[i], serverCfg.servers[n-1] = serverCfg.servers[n-1], nil
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serverCfg.servers = serverCfg.servers[:n-1]
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break
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}
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}
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sm.serverConfigValue.Store(serverCfg)
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}
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// resetRebalanceTimer assumes:
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//
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// 1) the serverConfigLock is already held by the caller.
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// 2) the caller will call serverConfigValue.Store()
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func (sc *serverConfig) resetRebalanceTimer(sm *ServerManager) {
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numConsulServers := len(sc.servers)
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// Limit this connection's life based on the size (and health) of the
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// cluster. Never rebalance a connection more frequently than
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// connReuseLowWatermarkDuration, and make sure we never exceed
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// clusterWideRebalanceConnsPerSec operations/s across numLANMembers.
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clusterWideRebalanceConnsPerSec := float64(numConsulServers * newRebalanceConnsPerSecPerServer)
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connReuseLowWatermarkDuration := clientRPCMinReuseDuration + lib.RandomStagger(clientRPCMinReuseDuration/clientRPCJitterFraction)
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numLANMembers := 16384 // Assume sufficiently large for now. FIXME: numLanMembers := len(c.LANMembers())
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connRebalanceTimeout := lib.RateScaledInterval(clusterWideRebalanceConnsPerSec, connReuseLowWatermarkDuration, numLANMembers)
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sm.logger.Printf("[DEBUG] consul: connection will be rebalanced in %v", connRebalanceTimeout)
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sc.rebalanceTimer.Reset(connRebalanceTimeout)
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}
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// StartServerManager is used to start and manage the task of automatically
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// shuffling and rebalance the list of consul servers. This maintenance
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// happens either when a new server is added or when a duration has been
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// exceed.
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func (sm *ServerManager) StartServerManager() {
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var rebalanceTimer *time.Timer
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func() {
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sm.serverConfigLock.Lock()
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defer sm.serverConfigLock.Unlock()
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serverCfgPtr := sm.serverConfigValue.Load()
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if serverCfgPtr == nil {
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panic("server config has not been initialized")
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}
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var serverCfg serverConfig
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serverCfg = serverCfgPtr.(serverConfig)
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2016-02-20 02:59:35 +00:00
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serverCfg.resetRebalanceTimer(sm)
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rebalanceTimer = serverCfg.rebalanceTimer
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sm.serverConfigValue.Store(serverCfg)
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2016-02-20 01:32:16 +00:00
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}()
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for {
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select {
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case e := <-sm.consulServersCh:
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switch e {
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case consulServersNodeJoin:
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sm.logger.Printf("[INFO] consul: new node joined cluster")
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sm.RebalanceServers()
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case consulServersRebalance:
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sm.logger.Printf("[INFO] consul: rebalancing servers by request")
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sm.RebalanceServers()
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case consulServersRPCError:
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sm.logger.Printf("[INFO] consul: need to find a new server to talk with")
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sm.CycleFailedServers()
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// FIXME(sean@): wtb preemptive Status.Ping
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// of servers, ideally parallel fan-out of N
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// nodes, then settle on the first node which
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|
|
|
// responds successfully.
|
|
|
|
//
|
|
|
|
// Is there a distinction between slow and
|
|
|
|
// offline? Do we run the Status.Ping with a
|
|
|
|
// fixed timeout (say 30s) that way we can
|
|
|
|
// alert administrators that they've set
|
|
|
|
// their RPC time too low even though the
|
|
|
|
// Ping did return successfully?
|
|
|
|
default:
|
|
|
|
sm.logger.Printf("[WARN] consul: unhandled LAN Serf Event: %#v", e)
|
|
|
|
}
|
|
|
|
case <-rebalanceTimer.C:
|
|
|
|
sm.logger.Printf("[INFO] consul: server rebalance timeout")
|
|
|
|
sm.RebalanceServers()
|
|
|
|
|
|
|
|
case <-sm.shutdownCh:
|
|
|
|
return
|
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|