open-consul/agent/proxy/daemon.go

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package proxy
import (
"fmt"
"log"
"os"
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"os/exec"
"sync"
"time"
)
// Constants related to restart timers with the daemon mode proxies. At some
// point we will probably want to expose these knobs to an end user, but
// reasonable defaults are chosen.
const (
DaemonRestartHealthy = 10 * time.Second // time before considering healthy
DaemonRestartBackoffMin = 3 // 3 attempts before backing off
DaemonRestartMaxWait = 1 * time.Minute // maximum backoff wait time
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)
// Daemon is a long-running proxy process. It is expected to keep running
// and to use blocking queries to detect changes in configuration, certs,
// and more.
//
// Consul will ensure that if the daemon crashes, that it is restarted.
type Daemon struct {
// Command is the command to execute to start this daemon. This must
// be a Cmd that isn't yet started.
Command *exec.Cmd
// ProxyToken is the special local-only ACL token that allows a proxy
// to communicate to the Connect-specific endpoints.
ProxyToken string
// Logger is where logs will be sent around the management of this
// daemon. The actual logs for the daemon itself will be sent to
// a file.
Logger *log.Logger
// process is the started process
lock sync.Mutex
process *os.Process
stopCh chan struct{}
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}
// Start starts the daemon and keeps it running.
//
// This function returns after the process is successfully started.
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func (p *Daemon) Start() error {
p.lock.Lock()
defer p.lock.Unlock()
// If the daemon is already started, return no error.
if p.stopCh != nil {
return nil
}
// Start it for the first time
process, err := p.start()
if err != nil {
return err
}
// Create the stop channel we use to notify when we've gracefully stopped
stopCh := make(chan struct{})
p.stopCh = stopCh
// Store the process so that we can signal it later
p.process = process
go p.keepAlive(stopCh)
return nil
}
func (p *Daemon) keepAlive(stopCh chan struct{}) {
p.lock.Lock()
process := p.process
p.lock.Unlock()
// attemptsDeadline is the time at which we consider the daemon to have
// been alive long enough that we can reset the attempt counter.
//
// attempts keeps track of the number of restart attempts we've had and
// is used to calculate the wait time using an exponential backoff.
var attemptsDeadline time.Time
var attempts uint
for {
if process == nil {
// If we're passed the attempt deadline then reset the attempts
if !attemptsDeadline.IsZero() && time.Now().After(attemptsDeadline) {
attempts = 0
}
attemptsDeadline = time.Now().Add(DaemonRestartHealthy)
attempts++
// Calculate the exponential backoff and wait if we have to
if attempts > DaemonRestartBackoffMin {
waitTime := (1 << (attempts - DaemonRestartBackoffMin)) * time.Second
if waitTime > DaemonRestartMaxWait {
waitTime = DaemonRestartMaxWait
}
if waitTime > 0 {
p.Logger.Printf(
"[WARN] agent/proxy: waiting %s before restarting daemon",
waitTime)
time.Sleep(waitTime)
}
}
p.lock.Lock()
// If we gracefully stopped (stopCh is closed) then don't restart. We
// check stopCh and not p.stopCh because the latter could reference
// a new process.
select {
case <-stopCh:
p.lock.Unlock()
return
default:
}
// Process isn't started currently. We're restarting.
var err error
process, err = p.start()
if err != nil {
p.Logger.Printf("[ERR] agent/proxy: error restarting daemon: %s", err)
}
p.process = process
p.lock.Unlock()
}
_, err := process.Wait()
process = nil
p.Logger.Printf("[INFO] agent/proxy: daemon exited: %s", err)
}
}
// start starts and returns the process. This will create a copy of the
// configured *exec.Command with the modifications documented on Daemon
// such as setting the proxy token environmental variable.
func (p *Daemon) start() (*os.Process, error) {
cmd := *p.Command
// Add the proxy token to the environment. We first copy the env because
// it is a slice and therefore the "copy" above will only copy the slice
// reference. We allocate an exactly sized slice.
cmd.Env = make([]string, len(p.Command.Env), len(p.Command.Env)+1)
copy(cmd.Env, p.Command.Env)
cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%s", EnvProxyToken, p.ProxyToken))
// Start it
err := cmd.Start()
return cmd.Process, err
}
// Stop stops the daemon.
//
// This will attempt a graceful stop (SIGINT) before force killing the
// process (SIGKILL). In either case, the process won't be automatically
// restarted unless Start is called again.
//
// This is safe to call multiple times. If the daemon is already stopped,
// then this returns no error.
func (p *Daemon) Stop() error {
p.lock.Lock()
defer p.lock.Unlock()
// If we don't have a stopCh then we never even started yet.
if p.stopCh == nil {
return nil
}
// If stopCh is closed, then we're already stopped
select {
case <-p.stopCh:
return nil
default:
}
err := p.process.Signal(os.Interrupt)
// This signals that we've stopped and therefore don't want to restart
close(p.stopCh)
p.stopCh = nil
return err
//return p.Command.Process.Kill()
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}