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
// note that this value interacts with serfConfig.LeavePropagateDelay
gracefulTimeout = 5 * 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.Fatal("[WARN] cascade: non-graceful leave detected")
}
// 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)
// TODO: how should cascade handle name conflicts?
// defaulting to just blowing up for now, but
// we _could_ take the tailscale route & append
// -1 or whatever to the node. that would be more user friendly.
// TODO: some of these serf settings were pulled
// from consul[1]. re-examine them eventually.
serfConfig.EnableNameConflictResolution = false
serfConfig.LeavePropagateDelay = 3 * time.Second
serfConfig.MinQueueDepth = 4096
serfConfig.QueueDepthWarning = 1000000
serfConfig.ReconnectTimeout = 3 * 24 * time.Hour
serfConfig.MemberlistConfig = memberlist.DefaultWANConfig()
serfConfig.MemberlistConfig.DeadNodeReclaimTime = 30 * time.Second
serfConfig.MemberlistConfig.BindAddr = bindIP
serfConfig.MemberlistConfig.BindPort = bindPort
agent := Create(serfConfig)
return agent
}
// [1]: sources for consul serf tweaks
// https://github.com/hashicorp/consul/blob/v1.14.4/agent/consul/config.go
// https://github.com/hashicorp/consul/blob/v1.14.4/lib/serf/serf.go