einhorn

#!/usr/bin/env ruby
# Author: Greg Brockman <gdb@stripe.com>

require 'rubygems'
require 'einhorn'

module Einhorn
  module Executable
    def self.einhorn_usage(long)
      usage = <<EOF
## Usage

Einhorn is the language-independent shared socket manager. Run
`einhorn -h` to see detailed usage. At a high level, usage looks like
the following:

    einhorn [options] program

Einhorn will open one or more shared sockets and run multiple copies
of your process. You can seamlessly reload your code, dynamically
reconfigure Einhorn, and more.
EOF

      if long
        usage << <<EOF

## Overview

To set Einhorn up as a master process running 3 copies of `sleep 5`:

    $ einhorn -n 3 sleep 5

You can communicate your running Einhorn process via `einhornsh`:

    $ einhornsh
    Welcome gdb! You are speaking to Einhorn Master Process 11902
    Enter 'help' if you're not sure what to do.

    Type "quit" or "exit" to quit at any time
    > help
    You are speaking to the Einhorn command socket. You can run the following commands:
    ...

### Server sockets

If your process is a server and listens on one or more sockets,
Einhorn can open these sockets and pass them to the workers. You can
specify the addresses to bind by passing one or more `-b ADDR`
arguments:

    einhorn -b 127.0.0.1:1234 my-command
    einhorn -b 127.0.0.1:1234,r -b 127.0.0.1:1235 my-command

Each address is specified as an ip/port pair, possibly accompanied by options:

    ADDR := (IP:PORT)[<,OPT>...]

In the worker process, the opened file descriptors will be represented
as a space-separated list of file descriptor numbers in the
EINHORN_FDS environment variable (respecting the order that the `-b`
options were provided in):

    EINHORN_FDS="6" # 127.0.0.1:1234
    EINHORN_FDS="6 7" # 127.0.0.1:1234,r 127.0.0.1:1235

Valid opts are:

    r, so_reuseaddr: set SO_REUSEADDR on the server socket
    n, o_nonblock: set O_NONBLOCK on the server socket

You can for example run:

    $ einhorn -b 127.0.0.1:2345,r -m manual -n 4 -- example/time_server

Which will run 4 copies of

    EINHORN_FDS=6 example/time_server

Where file descriptor 6 is a server socket bound to `127.0.0.1:2345`
and with `SO_REUSEADDR` set. It is then your application's job to
figure out how to `accept()` on this file descriptor.

### Command socket

Einhorn opens a UNIX socket to which you can send commands (run
`help` in `einhornsh` to see what admin commands you can
run). Einhorn relies on file permissions to ensure that no malicious
users can gain access. Run with a `-d DIRECTORY` to change the
directory where the socket will live.

Note that the command socket uses a line-oriented YAML protocol, and
you should ensure you trust clients to send arbitrary YAML messages
into your process.

### Seamless upgrades

You can cause your code to be seamlessly reloaded by upgrading the
worker code on disk and running

    $ einhornsh
    ...
    > upgrade

Once the new workers have been spawned, Einhorn will send each old
worker a SIGUSR2. SIGUSR2 should be interpreted as a request for a
graceful shutdown.

### ACKs

After Einhorn spawns a worker, it will only consider the worker up
once it has received an ACK. Currently two ACK mechanisms are
supported: manual and timer.

#### Manual ACK

A manual ACK (configured by providing a `-m manual`) requires your
application to send a command to the command socket once it's
ready. This is the safest ACK mechanism. If you're writing in Ruby,
just do

    require 'einhorn/worker'
    Einhorn::Worker.ack!

in your worker code. If you're writing in a different language, or
don't want to include Einhorn in your namespace, you can send the
string

    {"command":"worker:ack", "pid":PID}

to the UNIX socket pointed to by the environment variable
`EINHORN_SOCK_PATH`. (Be sure to include a trailing newline.)

To make things even easier, you can pass a `-g` to Einhorn, in which
case you just need to `write()` the above message to the open file
descriptor pointed to by `EINHORN_SOCK_FD`.

(See `lib/einhorn/worker.rb` for details of these and other socket
discovery mechanisms.)

#### Timer ACK [default]

By default, Einhorn will use a timer ACK of 1 second. That means that
if your process hasn't exited after 1 second, it is considered ACK'd
and healthy. You can modify this timeout to be more appropriate for
your application (and even set to 0 if desired). Just pass a `-m
FLOAT`.

### Preloading

If you're running a Ruby process, Einhorn can optionally preload its
code, so it only has to load the code once per upgrade rather than
once per worker process. This also saves on memory overhead, since all
of the code in these processes will be stored only once using your
operating system's copy-on-write features.

To use preloading, just give Einhorn a `-p PATH_TO_CODE`, and make
sure you've defined an `einhorn_main` method.

In order to maximize compatibility, we've worked to minimize Einhorn's
dependencies. It has no dependencies outside of the Ruby standard
library.

### Command name

You can set the name that Einhorn and your workers show in PS. Just
pass `-c <name>`.
EOF
    end

    usage << <<EOF

### Options

EOF
    end
  end
end

# Would be nice if this could be loadable rather than always
# executing, but when run under gem it's a bit hard to do so.
if true # $0 == __FILE__
  Einhorn::TransientState.script_name = $0
  Einhorn::TransientState.argv = ARGV.dup
  Einhorn::TransientState.environ = ENV.to_hash

  optparse = OptionParser.new do |opts|
    opts.on('-b ADDR', '--bind ADDR', 'Bind an address and add the corresponding FD to EINHORN_FDS') do |addr|
      unless addr =~ /\A([^:]+):(\d+)((?:,\w+)*)\Z/
        raise "Invalid value for #{addr.inspect}: bind address must be of the form address:port[,flags...]"
      end

      host = $1
      port = Integer($2)
      flags = $3.split(',').select {|flag| flag.length > 0}.map {|flag| flag.downcase}
      Einhorn::State.bind << [host, port, flags]
    end

    opts.on('-c CMD_NAME', '--command-name CMD_NAME', 'Set the command name in ps to this value') do |cmd_name|
      Einhorn::State.cmd_name = cmd_name
    end

    opts.on('-d PATH', '--socket-path PATH', 'Where to open the Einhorn command socket') do |path|
      Einhorn::State.socket_path = path
    end

    opts.on('-e PIDFILE', '--pidfile PIDFILE', 'Where to write out the Einhorn pidfile') do |pidfile|
      Einhorn::State.pidfile = pidfile
    end

    opts.on('-f LOCKFILE', '--lockfile LOCKFILE', 'Where to store the Einhorn lockfile') do |lockfile|
      Einhorn::State.lockfile = lockfile
    end

    opts.on('-g', '--command-socket-as-fd', 'Leave the command socket open as a file descriptor, passed in the EINHORN_SOCK_FD environment variable. This allows your worker processes to ACK without needing to know where on the filesystem the command socket lives.') do
      Einhorn::State.command_socket_as_fd = true
    end

    opts.on('-h', '--help', 'Display this message') do
      opts.banner = Einhorn::Executable.einhorn_usage(true)
      puts opts
      exit(1)
    end

    opts.on('-k', '--kill-children-on-exit', 'If Einhorn exits unexpectedly, gracefully kill all its children') do
      Einhorn::State.kill_children_on_exit = true
    end

    opts.on('-l', '--backlog N', 'Connection backlog (assuming this is a server)') do |b|
      Einhorn::State.config[:backlog] = b.to_i
    end

    opts.on('-m MODE', '--ack-mode MODE', 'What kinds of ACK to expect from workers. Choices: FLOAT (number of seconds until assumed alive), manual (process will speak to command socket when ready). Default is MODE=1.') do |mode|
      # Try manual
      if mode == 'manual'
        Einhorn::State.ack_mode = {:type => :manual}
        next
      end

      # Try float
      begin
        parsed = Float(mode)
      rescue ArgumentError
      else
        Einhorn::State.ack_mode = {:type => :timer, :timeout => parsed}
        next
      end

      # Give up
      raise "Invalid ack-mode #{mode.inspect} (valid modes: FLOAT or manual)"
    end

    opts.on('-n', '--number N', 'Number of copies to spin up') do |n|
      Einhorn::State.config[:number] = n.to_i
    end

    opts.on('-p PATH', '--preload PATH', 'Load this code into memory, and fork but do not exec upon spawn. Must define an "einhorn_main" method') do |path|
      Einhorn::State.path = path
    end

    opts.on('-q', '--quiet', 'Make output quiet (can be reconfigured on the fly)') do
      Einhorn::Command.louder(false)
    end

    opts.on('-s', '--seconds N', 'Number of seconds to wait until respawning') do |b|
      Einhorn::State.config[:seconds] = s.to_i
    end

    opts.on('-v', '--verbose', 'Make output verbose (can be reconfigured on the fly)') do
      Einhorn::Command.louder(false)
    end

    opts.on('--with-state-fd STATE', '[Internal option] With file descriptor containing state') do |fd|
      Einhorn::TransientState.stateful = true
      read = IO.for_fd(Integer(fd))
      state = read.read
      read.close

      Einhorn.restore_state(state)
    end

    opts.on('--version', 'Show version') do
      puts Einhorn::VERSION
      exit
    end
  end
  optparse.order!

  if ARGV.length < 1
    optparse.banner = Einhorn::Executable.einhorn_usage(false)
    puts optparse
    exit(1)
  end

  ret = Einhorn.run
  begin
    exit(ret)
  rescue TypeError
    exit(0)
  end
end