main.go
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// design touchstones // configured entirely via environment variables // minimal configurable options // a single global cluster // easy cluster formation // todo // dns resolver for services package main import ( "fmt" "log" "os" "os/signal" "strings" "syscall" "time" "github.com/hashicorp/memberlist" "github.com/hashicorp/serf/serf" ) const ( // gracefulTimeout controls how long we wait before forcefully terminating gracefulTimeout = 3 * time.Second ) func main() { config := readConfig() agent := setupAgent(config) if err := agent.Start(); err != nil { log.Panic(err) } defer agent.Shutdown() // join any specified startup nodes if err := startupJoin(config, agent); err != nil { log.Panic(err) } if err := handleSignals(config, agent); err != nil { log.Panic(err) } } // handleSignals blocks until we get an exit-causing signal func handleSignals(config *Config, agent *Agent) error { signalCh := make(chan os.Signal, 4) signal.Notify(signalCh, os.Interrupt, syscall.SIGTERM) // Wait for a signal var sig os.Signal select { case s := <-signalCh: sig = s case <-agent.ShutdownCh(): // Agent is already shutdown! return nil } log.Printf("Caught signal: %v", sig) // Check if we should do a graceful leave graceful := false if sig == os.Interrupt || sig == syscall.SIGTERM { graceful = true } // Bail fast if not doing a graceful leave if !graceful { log.Printf("[WARN] cascade: non-graceful leave detected") return nil } // Attempt a graceful leave gracefulCh := make(chan struct{}) log.Println("Gracefully shutting down agent...") go func() { if err := agent.Leave(); err != nil { log.Printf("Error: %s", err) return } close(gracefulCh) }() // Wait for leave or another signal select { case <-signalCh: return fmt.Errorf("[WARN] cascade: idk") case <-time.After(gracefulTimeout): return fmt.Errorf("[WARN] cascade: leave timed out") case <-gracefulCh: return nil } } func readConfig() *Config { config := DefaultConfig() // CASCADE_BIND=127.0.0.1:1234 if os.Getenv("CASCADE_BIND") != "" { config.BindAddr = os.Getenv("CASCADE_BIND") } // CASCADE_JOIN=127.0.0.1,127.0.0.5 if os.Getenv("CASCADE_JOIN") != "" { config.StartJoin = strings.Split(os.Getenv("CASCADE_JOIN"), ",") } // CASCADE_NAME=nostromo.j3s.sh if os.Getenv("CASCADE_NAME") != "" { config.NodeName = os.Getenv("CASCADE_NAME") } return config } func startupJoin(config *Config, agent *Agent) error { if len(config.StartJoin) == 0 { return nil } log.Printf("Joining cluster...") n, err := agent.Join(config.StartJoin) if err != nil { return err } log.Printf("Join completed. Synced with %d initial agents", n) return nil } func setupAgent(config *Config) *Agent { bindIP, bindPort, err := config.AddrParts(config.BindAddr) if err != nil { log.Panic(err) } serfConfig := serf.DefaultConfig() serfConfig.NodeName = config.NodeName serfConfig.ProtocolVersion = uint8(serf.ProtocolVersionMax) serfConfig.CoalescePeriod = 3 * time.Second serfConfig.QuiescentPeriod = time.Second serfConfig.QueryResponseSizeLimit = 1024 serfConfig.QuerySizeLimit = 1024 serfConfig.UserEventSizeLimit = 512 serfConfig.UserCoalescePeriod = 3 * time.Second serfConfig.UserQuiescentPeriod = time.Second // TODO: look at reconnect/tombstone settings w more scrutiny serfConfig.ReconnectInterval = 0 serfConfig.ReconnectTimeout = 0 serfConfig.TombstoneTimeout = 0 serfConfig.BroadcastTimeout = 0 // TODO: what are the implications of true here o_O serfConfig.EnableNameConflictResolution = true // hardcode DefaultWANConfig because cascade is designed to be // used as a single global system. serfConfig.MemberlistConfig = memberlist.DefaultWANConfig() serfConfig.MemberlistConfig.BindAddr = bindIP serfConfig.MemberlistConfig.BindPort = bindPort serfConfig.MemberlistConfig.AdvertiseAddr = "" serfConfig.MemberlistConfig.AdvertisePort = 0 agent := Create(serfConfig) return agent }