Class: Frankenstein::Server

Inherits:
Object
  • Object
show all
Defined in:
lib/frankenstein/server.rb,
lib/frankenstein/server/webrick_logger.rb

Overview

A straightforward Prometheus metrics server.

When you're looking to instrument your application which isn't, itself, a HTTP service, you need this class. It spawns a WEBrick server on a port you specify, and gives you a registry to put your metrics into. That's pretty much it.

The simplest example possible:

stats_server = Frankenstein::Server.new
stats_server.run   # We are now serving stats on port 8080!
counter = stats_server.registry.counter(:seconds_count, "Number of seconds")
# Give the counter something to count
loop { sleep 1; counter.increment({}) }

Now if you hit http://localhost:8080/metrics you should see a counter gradually going up, along with stats about the Frankenstein HTTP server itself. Neato!

You can change how the webserver logs, and the port it listens on, with options to #new. If for some reason you need to shut down the webserver manually, use

shutdown.

Defined Under Namespace

Classes: AlreadyRunningError, WEBrickLogger

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(port: 8080, logger: nil, metrics_prefix: "frankenstein_server", registry: Prometheus::Client::Registry.new) ⇒ Server

Create a new server instance.

Parameters:

  • port (Integer) (defaults to: 8080) —

    the TCP to listen on.

  • logger (Logger) (defaults to: nil) —

    send log messages from WEBrick to this logger. If not specified, all log messages will be silently eaten.

  • metrics_prefix (#to_s) (defaults to: "frankenstein_server") —

    The prefix to apply to the metrics exposed instrumenting the metrics server itself.

  • registry (Prometheus::Client::Registry) (defaults to: Prometheus::Client::Registry.new) —

    if you want to use an existing metrics registry for this server, pass it in here. Otherwise, a new one will be created for you, and be made available via #registry.



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# File 'lib/frankenstein/server.rb', line 59

def initialize(port: 8080, logger: nil, metrics_prefix: "frankenstein_server", registry: Prometheus::Client::Registry.new)
  @port           = port
  @logger         = logger || Logger.new(RbConfig::CONFIG['host_os'] =~ /mingw|mswin/ ? 'NUL' : '/dev/null')
  @metrics_prefix = metrics_prefix
  @registry       = registry

  @op_mutex = Mutex.new
  @op_cv    = ConditionVariable.new
end

Instance Attribute Details

#registry ⇒ Object (readonly)

The instance of Prometheus::Client::Registry that contains the metrics that will be presented by this instance of Frankenstein::Server.



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# File 'lib/frankenstein/server.rb', line 43

def registry
  @registry
end

Instance Method Details

#run ⇒ Object

Start the server instance running.

This method will return only after #shutdown is called (presumably from another thread).



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# File 'lib/frankenstein/server.rb', line 74

def run
  @op_mutex.synchronize do
    return AlreadyRunningError if @server

    begin
      wrapped_logger = Frankenstein::Server::WEBrickLogger.new(logger: @logger, progname: "Frankenstein::Server")
      @server = WEBrick::HTTPServer.new(Logger: wrapped_logger, BindAddress: nil, Port: @port, AccessLog: [[wrapped_logger, WEBrick::AccessLog::COMMON_LOG_FORMAT]])
      @server.mount "/", Rack::Handler::WEBrick, app
    rescue => ex
      #:nocov:
      @logger.fatal("Frankenstein::Server#run") { (["Exception while trying to create WEBrick::HTTPServer: #{ex.message} (#{ex.class})"] + ex.backtrace).join("\n  ") }
      #:nocov:
    ensure
      @op_cv.signal
    end
  end

  begin
    @server.start if @server
  rescue => ex
    #:nocov:
    @logger.fatal("Frankenstein::Server#run") { (["Exception while running WEBrick::HTTPServer: #{ex.message} (#{ex.class})"] + ex.backtrace).join("\n  ") }
    #:nocov:
  end
end

#shutdown ⇒ Object

Terminate a running server instance.

If the server isn't currently running, this call is a no-op.



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# File 'lib/frankenstein/server.rb', line 104

def shutdown
  @op_mutex.synchronize do
    return nil if @server.nil?
    @server.shutdown
    @server = nil
  end
end