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github.com/cloudflare/tableflip

Package tableflip

v1.2.0
Latest Go to latest
Published: Apr 30, 2020 | License: BSD-3-Clause | Module: github.com/cloudflare/tableflip

Overview

Package tableflip implements zero downtime upgrades.

An upgrade spawns a new copy of argv[0] and passes file descriptors of used listening sockets to the new process. The old process exits once the new process signals readiness. Thus new code can use sockets allocated in the old process. This is similar to the approach used by nginx, but as a library.

At any point in time there are one or two processes, with at most one of them in non-ready state. A successful upgrade fully replaces all old configuration and code.

To use this library with systemd you need to use the PIDFile option in the service file.

[Unit]
Description=Service using tableflip

[Service]
ExecStart=/path/to/binary -some-flag /path/to/pid-file
ExecReload=/bin/kill -HUP $MAINPID
PIDFile=/path/to/pid-file

Then pass /path/to/pid-file to New. You can use systemd-run to test your implementation:

systemd-run --user -p PIDFile=/path/to/pid-file /path/to/binary

systemd-run will print a unit name, which you can use with systemctl to inspect the service.

NOTES:

Requires at least Go 1.9, since there is a race condition on the pipes used for communication between parent and child.

If you're seeing "can't start process: no such file or directory", you're probably using "go run main.go", for graceful reloads to work, you'll need use "go build main.go".

Tableflip does not work on Windows, because Windows does not have the mechanisms required to support this method of graceful restarting. It is still possible to include this package in code that runs on Windows, which may be necessary in certain development circumstances, but it will not provide zero downtime upgrades when running on Windows. See the `testing` package for an example of how to use it.

Example (HttpShutdown)

This shows how to use the upgrader with the graceful shutdown facilities of net/http.

Code:

var (
	listenAddr = flag.String("listen", "localhost:8080", "`Address` to listen on")
	pidFile    = flag.String("pid-file", "", "`Path` to pid file")
)

flag.Parse()
log.SetPrefix(fmt.Sprintf("%d ", os.Getpid()))

upg, err := tableflip.New(tableflip.Options{
	PIDFile: *pidFile,
})
if err != nil {
	panic(err)
}
defer upg.Stop()

go func() {
	sig := make(chan os.Signal, 1)
	signal.Notify(sig, syscall.SIGHUP)
	for range sig {
		err := upg.Upgrade()
		if err != nil {
			log.Println("Upgrade failed:", err)
		}
	}
}()

ln, err := upg.Listen("tcp", *listenAddr)
if err != nil {
	log.Fatalln("Can't listen:", err)
}

server := http.Server{}

go func() {
	err := server.Serve(ln)
	if err != http.ErrServerClosed {
		log.Println("HTTP server:", err)
	}
}()

log.Printf("ready")
if err := upg.Ready(); err != nil {
	panic(err)
}
<-upg.Exit()

time.AfterFunc(30*time.Second, func() {
	log.Println("Graceful shutdown timed out")
	os.Exit(1)
})

server.Shutdown(context.Background())
Example (TcpServer)

This shows how to use the Upgrader with a listener based service.

Code:

var (
	listenAddr = flag.String("listen", "localhost:8080", "`Address` to listen on")
	pidFile    = flag.String("pid-file", "", "`Path` to pid file")
)

flag.Parse()
log.SetPrefix(fmt.Sprintf("%d ", os.Getpid()))

upg, err := tableflip.New(tableflip.Options{
	PIDFile: *pidFile,
})
if err != nil {
	panic(err)
}
defer upg.Stop()

go func() {
	sig := make(chan os.Signal, 1)
	signal.Notify(sig, syscall.SIGHUP)
	for range sig {
		err := upg.Upgrade()
		if err != nil {
			log.Println("upgrade failed:", err)
		}
	}
}()

ln, err := upg.Fds.Listen("tcp", *listenAddr)
if err != nil {
	log.Fatalln("Can't listen:", err)
}

go func() {
	defer ln.Close()

	log.Printf("listening on %s", ln.Addr())

	for {
		c, err := ln.Accept()
		if err != nil {
			return
		}

		go func() {
			c.SetDeadline(time.Now().Add(time.Second))
			c.Write([]byte("It is a mistake to think you can solve any major problems just with potatoes.\n"))
			c.Close()
		}()
	}
}()

log.Printf("ready")
if err := upg.Ready(); err != nil {
	panic(err)
}
<-upg.Exit()

Index

Examples

Package Files

Constants

const DefaultUpgradeTimeout time.Duration = time.Minute

DefaultUpgradeTimeout is the duration before the Upgrader kills the new process if no readiness notification was received.

Variables

var ErrNotSupported = errors.New("tableflip: platform does not support graceful restart")

type Conn

type Conn interface {
	net.Conn
	syscall.Conn
}

Conn can be shared between processes.

type Fds

type Fds struct {
	// contains filtered or unexported fields
}

Fds holds all file descriptors inherited from the parent process.

func (*Fds) AddConn

func (f *Fds) AddConn(network, addr string, conn Conn) error

AddConn adds a connection.

It is safe to close conn after calling this method.

func (*Fds) AddFile

func (f *Fds) AddFile(name string, file *os.File) error

AddFile adds a file.

Until Go 1.12, file will be in blocking mode after this call.

func (*Fds) AddListener

func (f *Fds) AddListener(network, addr string, ln Listener) error

AddListener adds a listener.

It is safe to close ln after calling the method. Any existing listener with the same address is overwitten.

func (*Fds) AddPacketConn

func (f *Fds) AddPacketConn(network, addr string, conn PacketConn) error

AddPacketConn adds a PacketConn.

It is safe to close conn after calling the method. Any existing packet connection with the same address is overwitten.

func (*Fds) Conn

func (f *Fds) Conn(network, addr string) (net.Conn, error)

Conn returns an inherited connection or nil.

It is safe to close the returned Conn.

func (*Fds) File

func (f *Fds) File(name string) (*os.File, error)

File returns an inherited file or nil.

The descriptor may be in blocking mode.

func (*Fds) Listen

func (f *Fds) Listen(network, addr string) (net.Listener, error)

Listen returns a listener inherited from the parent process, or creates a new one.

func (*Fds) ListenPacket

func (f *Fds) ListenPacket(network, addr string) (net.PacketConn, error)

ListenPacket returns a packet conn inherited from the parent process, or creates a new one.

func (*Fds) Listener

func (f *Fds) Listener(network, addr string) (net.Listener, error)

Listener returns an inherited listener or nil.

It is safe to close the returned listener.

func (*Fds) PacketConn

func (f *Fds) PacketConn(network, addr string) (net.PacketConn, error)

PacketConn returns an inherited packet connection or nil.

It is safe to close the returned packet connection.

type Listener

type Listener interface {
	net.Listener
	syscall.Conn
}

Listener can be shared between processes.

type Options

type Options struct {
	// Time after which an upgrade is considered failed. Defaults to
	// DefaultUpgradeTimeout.
	UpgradeTimeout time.Duration
	// The PID of a ready process is written to this file.
	PIDFile string
}

Options control the behaviour of the Upgrader.

type PacketConn

type PacketConn interface {
	net.PacketConn
	syscall.Conn
}

PacketConn can be shared between processes.

type Upgrader

type Upgrader struct {
	*Fds
	// contains filtered or unexported fields
}

Upgrader handles zero downtime upgrades and passing files between processes.

func New

func New(opts Options) (upg *Upgrader, err error)

New creates a new Upgrader. Files are passed from the parent and may be empty.

Only the first call to this function will succeed. May return ErrNotSupported.

func (*Upgrader) Exit

func (u *Upgrader) Exit() <-chan struct{}

Exit returns a channel which is closed when the process should exit.

func (*Upgrader) HasParent

func (u *Upgrader) HasParent() bool

HasParent checks if the current process is an upgrade or the first invocation.

func (*Upgrader) Ready

func (u *Upgrader) Ready() error

Ready signals that the current process is ready to accept connections. It must be called to finish the upgrade.

All fds which were inherited but not used are closed after the call to Ready.

func (*Upgrader) Stop

func (u *Upgrader) Stop()

Stop prevents any more upgrades from happening, and closes the exit channel.

If this function is called before a call to Upgrade() has succeeded, it is assumed that the process is being shut down completely. All Unix sockets known to Upgrader.Fds are then unlinked from the filesystem.

func (*Upgrader) Upgrade

func (u *Upgrader) Upgrade() error

Upgrade triggers an upgrade.

func (*Upgrader) WaitForParent

func (u *Upgrader) WaitForParent(ctx context.Context) error

WaitForParent blocks until the parent has exited.

Returns an error if the parent misbehaved during shutdown.

Documentation was rendered with GOOS=linux and GOARCH=amd64.

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