Class: Stalin::Adapter::Rack

Inherits:
Object
  • Object
show all
Defined in:
lib/stalin/adapter/rack.rb

Overview

A low-tech but reliable solution that invokes stalin using Rack middleware. This is suitable for application srvers that use a master-and-workers process architecture, wohse workers respond to a graceful shutdown signal, and whose masters spawn new workers as needed.

This functions as a base class for server-specific middlewares, and can be used if there is an app server that uses a signalling strategy not explicitly supported by Stalin.

Direct Known Subclasses

Puma, Unicorn

Constant Summary collapse

MB =

Conversion constant for human-readable memory amounts in log messages.

Float(1024**2)

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(app, graceful, abrupt, min = 1024**3, max = 2*1024**3, cycle = 16, verbose = false) ⇒ Rack

Create a middleware instance.

Parameters:

  • app (#call) —

    inner Rack application

  • graceful (Symbol) —

    name of graceful-shutdown signal

  • abrupt (Symbol) —

    name of abrupt-shutdown signal

  • min (Integer) (defaults to: 1024**3) —

    lower-bound worker memory consumption before restart

  • max (Integer) (defaults to: 2*1024**3) —

    upper-bound worker memory consumption before restart

  • cycle (Integer) (defaults to: 16) —

    how frequently to check memory consumption (# requests)

  • verbose (Boolean) (defaults to: false) —

    log extra information

  • signals (Array) —

    pair of two Symbol signal-names: one for “graceful shutdown please” and one for “terminate immediately”



51
52
53
54
55
56
57
58
59
 
# File 'lib/stalin/adapter/rack.rb', line 51

def initialize(app, graceful, abrupt, min=1024**3, max=2*1024**3, cycle=16, verbose=false)
  @app      = app
  @graceful = graceful
  @abrupt   = abrupt
  @min      = min
  @max      = max
  @cycle    = cycle
  @verbose  = verbose
end

Class Method Details

.new(*args) ⇒ Object

Construct a new middleware. If all six arguments are passed, construct an instance of this class; otherwise, use a heuristic to construct an instance of a suitable derived class.

Raises:

  • (ArgumentError) —

    if an incorrect number of arguments is passed

  • (RuntimeError) —

    if 0..5 arguments and the heuristic can’t figure out which signals to use



19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
 
# File 'lib/stalin/adapter/rack.rb', line 19

def self.new(*args)
  if self == Rack && args.length < 3 
    # Warn that this shim will go away in v1
    warn "Stalin::Adapter::Rack.new with fewer than 3 arguments is deprecated; please instantiate a derived class e.g. Unicorn or Puma"

    # Use a heuristic to decide on the correct adapter and instantiate a derived class.
    if defined?(::Unicorn)
      middleware = Unicorn.allocate
    elsif defined?(::Puma)
      middleware = Puma.allocate
    else
      raise RuntimeError, "Cannot determine a suitable Stalin adapter; please instantiate this class with six arguments"
    end

    # Initialize our new object (ugh)
    middleware.instance_eval { initialize(*args) }
    middleware
  else
    super 
  end
end

Instance Method Details

#call(env) ⇒ Object 



61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
 
# File 'lib/stalin/adapter/rack.rb', line 61

def call(env)
  result = @app.call(env)

  logger = logger_for(env)

  begin
    @lim     ||= @min + randomize(@max - @min + 1)
    @req     ||= 0
    @req     += 1

    if @req % @cycle == 0
      @req = 0
      @watcher ||= ::Stalin::Watcher.new(Process.pid)
      @killer  ||= ::Stalin::Killer.new(Process.pid, @graceful, @abrupt)
      if (used = @watcher.watch) > @lim
        sig = @killer.kill
        @watcher.watch
        logger.info "stalin (pid: %d) send SIG%s; memory usage %.1f MB > %.1f MB" %
                      [Process.pid, sig, used / MB, @lim / MB]
        @cycle = 2
      elsif @verbose
        logger.info "stalin (pid: %d) soldiers on; memory usage %.1f MB < %.1f MB" %
                       [Process.pid, used / MB, @lim / MB]
      end
    end
  rescue Exception => e
    logger.error "stalin (pid: %d) ERROR %s: %s (%s)" %
                  [Process.pid, e.class.name, e.message, e.backtrace.first]
  end

  result
end