open-nomad/command/agent/agent.go

package agent

import (
	"io"
	"log"
	"os"
	"sync"

	"github.com/hashicorp/nomad/nomad"
)

// Agent is a long running daemon that is used to run both
// clients and servers. Servers are responsible for managing
// state and making scheduling decisions. Clients can be
// scheduled to, and are responsible for interfacing with
// servers to run allocations.
type Agent struct {
	config    *Config
	logger    *log.Logger
	logOutput io.Writer

	server *nomad.Server
	client *nomad.Server // TODO

	shutdown     bool
	shutdownCh   chan struct{}
	shutdownLock sync.Mutex
}

// NewAgent is used to create a new agent with the given configuration
func NewAgent(config *Config, logOutput io.Writer) (*Agent, error) {
	// Ensure we have a log sink
	if logOutput == nil {
		logOutput = os.Stderr
	}

	a := &Agent{
		config:     config,
		logger:     log.New(logOutput, "", log.LstdFlags),
		logOutput:  logOutput,
		shutdownCh: make(chan struct{}),
	}
	return a, nil
}

// Leave is used gracefully exit. Clients will inform servers
// of their departure so that allocations can be rescheduled.
func (a *Agent) Leave() error {
	return nil
}

// Shutdown is used to terminate the agent.
func (a *Agent) Shutdown() error {
	a.shutdownLock.Lock()
	defer a.shutdownLock.Unlock()

	if a.shutdown {
		return nil
	}

	a.logger.Println("[INFO] agent: requesting shutdown")
	var err error
	if a.server != nil {
		err = a.server.Shutdown()
	} else {
		err = a.client.Shutdown()
	}

	a.logger.Println("[INFO] agent: shutdown complete")
	a.shutdown = true
	close(a.shutdownCh)
	return err
}

// RPC is used to make an RPC call to the Nomad servers
func (a *Agent) RPC(method string, args interface{}, reply interface{}) error {
	if a.server != nil {
		return a.server.RPC(method, args, reply)
	}
	return a.client.RPC(method, args, reply)
}