From 9b8767aa678b70c1e840d36ea2003e0ec43f1e78 Mon Sep 17 00:00:00 2001 From: Sean Chittenden Date: Fri, 19 Feb 2016 12:13:17 -0800 Subject: [PATCH] Refactor out the management of Consul servers Move the management of c.consulServers (fka c.consuls) into consul/server_manager.go. This commit brings in a background task that proactively manages the server list and: *) reshuffles the list *) manages the timer out of the RPC() path *) uses atomics to detect a server has failed This is a WIP, more work in testing needs to be completed. --- consul/server_manager.go | 212 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 212 insertions(+) create mode 100644 consul/server_manager.go diff --git a/consul/server_manager.go b/consul/server_manager.go new file mode 100644 index 0000000000..35023b3464 --- /dev/null +++ b/consul/server_manager.go @@ -0,0 +1,212 @@ +package consul + +import ( + "math/rand" + "sync/atomic" + "time" + + "github.com/hashicorp/consul/lib" +) + +type consulServerEventTypes int + +const ( + // consulServersNodeJoin is used to notify of a new consulServer. + // The primary effect of this is a reshuffling of consulServers and + // finding a new preferredServer. + consulServersNodeJoin = iota + + // consulServersRebalance is used to signal we should rebalance our + // connection load across servers + consulServersRebalance + + // consulServersRPCError is used to signal when a server has either + // timed out or returned an error and we would like to have the + // server manager find a new preferredServer. + consulServersRPCError +) + +// serverCfg is the thread-safe configuration structure that is used to +// maintain the list of consul servers in Client. +// +// NOTE(sean@): We are explicitly relying on the fact that this is copied. +// Please keep this structure light. +type serverConfig struct { + // servers tracks the locally known servers + servers []*serverParts + + // Timer used to control rebalancing of servers + rebalanceTimer *time.Timer +} + +// consulServersManager is used to automatically shuffle and rebalance the +// list of consulServers. This maintenance happens either when a new server +// is added or when a duration has been exceed. +func (c *Client) consulServersManager() { + defaultTimeout := 5 * time.Second // FIXME(sean@): This is a bullshit value + var rebalanceTimer *time.Timer + func(c *Client) { + c.serverConfigMtx.Lock() + defer c.serverConfigMtx.Unlock() + + serverCfgPtr := c.serverConfigValue.Load() + if serverCfgPtr == nil { + panic("server config has not been initialized") + } + var serverCfg serverConfig + serverCfg = serverCfgPtr.(serverConfig) + rebalanceTimer = time.NewTimer(defaultTimeout) + serverCfg.rebalanceTimer = rebalanceTimer + }(c) + + for { + select { + case e := <-c.consulServersCh: + switch e { + case consulServersNodeJoin: + c.logger.Printf("[INFO] consul: new node joined cluster") + c.RebalanceServers() + case consulServersRebalance: + c.logger.Printf("[INFO] consul: rebalancing servers by request") + c.RebalanceServers() + case consulServersRPCError: + c.logger.Printf("[INFO] consul: need to find a new server to talk with") + c.CycleFailedServers() + // FIXME(sean@): wtb preemptive Status.Ping + // of servers, ideally parallel fan-out of N + // nodes, then settle on the first node which + // 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: + c.logger.Printf("[WARN] consul: unhandled LAN Serf Event: %#v", e) + } + case <-rebalanceTimer.C: + c.logger.Printf("[INFO] consul: server rebalance timeout") + c.RebalanceServers() + + case <-c.shutdownCh: + return + } + } +} + +func (c *Client) AddServer(server *serverParts) { + c.serverConfigMtx.Lock() + defer c.serverConfigMtx.Unlock() + serverCfg := c.serverConfigValue.Load().(serverConfig) + + // Check if this server is known + found := false + for idx, existing := range serverCfg.servers { + if existing.Name == server.Name { + // Overwrite the existing server parts in order to + // possibly update metadata (i.e. server version) + serverCfg.servers[idx] = server + found = true + break + } + } + + // Add to the list if not known + if !found { + serverCfg.servers = append(serverCfg.servers, server) + + // Notify the server maintenance task of a new server + c.consulServersCh <- consulServersNodeJoin + } + + c.serverConfigValue.Store(serverCfg) + +} + +func (c *Client) CycleFailedServers() { + c.serverConfigMtx.Lock() + defer c.serverConfigMtx.Unlock() + serverCfg := c.serverConfigValue.Load().(serverConfig) + + for i := range serverCfg.servers { + failCount := atomic.LoadUint64(&(serverCfg.servers[i].Disabled)) + if failCount == 0 { + break + } else if failCount > 0 { + serverCfg.servers = serverCfg.cycleServer() + } + } + + serverCfg.resetRebalanceTimer(c) + c.serverConfigValue.Store(serverCfg) +} + +func (sc *serverConfig) cycleServer() (servers []*serverParts) { + numServers := len(servers) + if numServers < 2 { + // No action required for zero or one server situations + return servers + } + + var failedNode *serverParts + failedNode, servers = servers[0], servers[1:] + servers = append(servers, failedNode) + return servers +} + +func (c *Client) RebalanceServers() { + c.serverConfigMtx.Lock() + defer c.serverConfigMtx.Unlock() + serverCfg := c.serverConfigValue.Load().(serverConfig) + + // Shuffle the server list on server join. Servers are selected from + // the head of the list and are moved to the end of the list on + // failure. + for i := len(serverCfg.servers) - 1; i > 0; i-- { + j := rand.Int31n(int32(i + 1)) + serverCfg.servers[i], serverCfg.servers[j] = serverCfg.servers[j], serverCfg.servers[i] + } + + serverCfg.resetRebalanceTimer(c) + c.serverConfigValue.Store(serverCfg) +} + +func (c *Client) RemoveServer(server *serverParts) { + c.serverConfigMtx.Lock() + defer c.serverConfigMtx.Unlock() + serverCfg := c.serverConfigValue.Load().(serverConfig) + + // Remove the server if known + n := len(serverCfg.servers) + for i := 0; i < n; i++ { + if serverCfg.servers[i].Name == server.Name { + serverCfg.servers[i], serverCfg.servers[n-1] = serverCfg.servers[n-1], nil + serverCfg.servers = serverCfg.servers[:n-1] + break + } + } + + c.serverConfigValue.Store(serverCfg) + +} + +// resetRebalanceTimer assumes: +// +// 1) the serverConfigMtx is already held by the caller. +// 2) the caller will call serverConfigValue.Store() +func (sc *serverConfig) resetRebalanceTimer(c *Client) { + numConsulServers := len(sc.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. + clusterWideRebalanceConnsPerSec := float64(numConsulServers * newRebalanceConnsPerSecPerServer) + connReuseLowWatermarkDuration := clientRPCMinReuseDuration + lib.RandomStagger(clientRPCMinReuseDuration/clientRPCJitterFraction) + numLANMembers := len(c.LANMembers()) + connRebalanceTimeout := lib.RateScaledInterval(clusterWideRebalanceConnsPerSec, connReuseLowWatermarkDuration, numLANMembers) + c.logger.Printf("[DEBUG] consul: connection will be rebalanced in %v", connRebalanceTimeout) + + sc.rebalanceTimer.Reset(connRebalanceTimeout) +}