open-nomad/client/client.go

package client

import (
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"strconv"
	"sync"
	"time"

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

const (
	// clientRPCCache controls how long we keep an idle connection
	// open to a server
	clientRPCCache = 30 * time.Second

	// clientMaxStreams controsl how many idle streams we keep
	// open to a server
	clientMaxStreams = 2
)

// RPCHandler can be provided to the Client if there is a local server
// to avoid going over the network. If not provided, the Client will
// maintain a connection pool to the servers
type RPCHandler interface {
	RPC(method string, args interface{}, reply interface{}) error
}

// Config is used to parameterize and configure the behavior of the client
type Config struct {
	// LogOutput is the destination for logs
	LogOutput io.Writer

	// Region is the clients region
	Region string

	// Servers is a list of known server addresses. These are as "host:port"
	Servers []string

	// RPCHandler can be provided to avoid network traffic if the
	// server is running locally.
	RPCHandler RPCHandler
}

// DefaultConfig returns the default configuration
func DefaultConfig() *Config {
	return &Config{
		LogOutput: os.Stderr,
	}
}

// Client is used to implement the client interaction with Nomad. Clients
// are expected to register as a schedulable node to the servers, and to
// run allocations as determined by the servers.
type Client struct {
	config *Config

	logger *log.Logger

	lastServer     net.Addr
	lastRPCTime    time.Time
	lastServerLock sync.Mutex

	connPool *nomad.ConnPool

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

// NewClient is used to create a new client from the given configuration
func NewClient(config *Config) (*Client, error) {
	// Create a logger
	logger := log.New(config.LogOutput, "", log.LstdFlags)

	c := &Client{
		config:     config,
		connPool:   nomad.NewPool(config.LogOutput, clientRPCCache, clientMaxStreams, nil),
		logger:     logger,
		shutdownCh: make(chan struct{}),
	}
	return c, nil
}

// Shutdown is used to tear down the client
func (c *Client) Shutdown() error {
	c.logger.Printf("[INFO] client: shutting down")
	c.shutdownLock.Lock()
	defer c.shutdownLock.Unlock()

	if c.shutdown {
		return nil
	}
	c.shutdown = true
	close(c.shutdownCh)
	return nil
}

// RPC is used to forward an RPC call to a nomad server, or fail if no servers
func (c *Client) RPC(method string, args interface{}, reply interface{}) error {
	// Invoke the RPCHandle if it exists
	if c.config.RPCHandler != nil {
		return c.config.RPCHandler.RPC(method, args, reply)
	}

	// Pick a server to request from
	addr, err := c.pickServer()
	if err != nil {
		return err
	}

	// Make the RPC request
	err = c.connPool.RPC(c.config.Region, addr, 1, method, args, reply)

	// Update the last server information
	c.lastServerLock.Lock()
	if err != nil {
		c.lastServer = nil
		c.lastRPCTime = time.Time{}
	} else {
		c.lastServer = addr
		c.lastRPCTime = time.Now()
	}
	c.lastServerLock.Unlock()
	return err
}

// pickServer is used to pick a target RPC server
func (c *Client) pickServer() (net.Addr, error) {
	c.lastServerLock.Lock()
	defer c.lastServerLock.Unlock()

	// Check for a valid last-used server
	if c.lastServer != nil && time.Now().Sub(c.lastRPCTime) < clientRPCCache {
		return c.lastServer, nil
	}

	// Bail if we can't find any servers
	if len(c.config.Servers) == 0 {
		return nil, fmt.Errorf("no known servers")
	}

	// Copy the list of servers and shuffle
	servers := make([]string, len(c.config.Servers))
	copy(servers, c.config.Servers)
	shuffleStrings(servers)

	// Try to resolve each server
	for i := 0; i < len(servers); i++ {
		addr, err := net.ResolveTCPAddr("tcp", servers[i])
		if err == nil {
			c.lastServer = addr
			c.lastRPCTime = time.Now()
			return addr, nil
		}
		c.logger.Printf("[WARN] client: failed to resolve '%s': %v", err)
	}

	// Bail if we reach this point
	return nil, fmt.Errorf("failed to resolve any servers")
}

// Stats is used to return statistics for debugging and insight
// for various sub-systems
func (c *Client) Stats() map[string]map[string]string {
	toString := func(v uint64) string {
		return strconv.FormatUint(v, 10)
	}
	stats := map[string]map[string]string{
		"nomad": map[string]string{
			"server":        "false",
			"known_servers": toString(uint64(len(c.config.Servers))),
		},
		"runtime": nomad.RuntimeStats(),
	}
	return stats
}