agent.go
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package main
import (
"fmt"
"log"
"sync"
"github.com/hashicorp/serf/serf"
)
// Agent starts and manages a Serf & adds
// service discovery
type Agent struct {
conf *Config
serfConf *serf.Config
eventCh chan serf.Event
// i doubt we care about handling events,
// but i'm leaving this here just in case
// eventHandlerList []EventHandler
// eventHandlersLock sync.Mutex
// This is the underlying Serf we are wrapping
serf *serf.Serf
// this channel receiving a signal = shutdown
shutdown bool
shutdownCh chan struct{}
shutdownLock sync.Mutex
}
func Create(conf *Config, serfConf *serf.Config) *Agent {
// Create a channel to listen for events from Serf
eventCh := make(chan serf.Event, 64)
serfConf.EventCh = eventCh
// Setup the agent
agent := &Agent{
conf: conf,
serfConf: serfConf,
eventCh: eventCh,
shutdownCh: make(chan struct{}),
}
return agent
}
func (a *Agent) eventLoop() {
serfShutdownCh := a.serf.ShutdownCh()
for {
select {
case e := <-a.eventCh:
log.Printf("[INFO] agent: Received event: %s", e.String())
case <-serfShutdownCh:
log.Printf("[WARN] agent: Serf shutdown detected, quitting")
a.Shutdown()
return
case <-a.shutdownCh:
return
}
}
}
func (a *Agent) Start() error {
log.Printf("[INFO] agent: Serf agent starting")
// Create serf first
serf, err := serf.Create(a.serfConf)
if err != nil {
return fmt.Errorf("Error creating Serf: %s", err)
}
a.serf = serf
// Start event loop
go a.eventLoop()
return nil
}
// Shutdown closes this agent and all of its processes. Should be preceded
// by a Leave for a graceful shutdown.
func (a *Agent) Shutdown() error {
a.shutdownLock.Lock()
defer a.shutdownLock.Unlock()
if a.shutdown {
return nil
}
if a.serf == nil {
goto EXIT
}
log.Println("[INFO] agent: requesting serf shutdown")
if err := a.serf.Shutdown(); err != nil {
return err
}
EXIT:
log.Println("[INFO] agent: shutdown complete")
a.shutdown = true
close(a.shutdownCh)
return nil
}
// Join asks the Serf instance to join. See the Serf.Join function.
func (a *Agent) Join(addrs []string, replay bool) (n int, err error) {
log.Printf("[INFO] agent: joining: %v replay: %v", addrs, replay)
ignoreOld := !replay
n, err = a.serf.Join(addrs, ignoreOld)
if n > 0 {
log.Printf("[INFO] agent: joined: %d nodes", n)
}
if err != nil {
log.Printf("[WARN] agent: error joining: %v", err)
}
return
}
// Leave prepares for a graceful shutdown of the agent and its processes
func (a *Agent) Leave() error {
if a.serf == nil {
return nil
}
log.Println("[INFO] agent: requesting graceful leave from Serf")
return a.serf.Leave()
}