RubyでgRPCサーバのAuto Reloadをする

Posted 2021-01-1 7 min read.

RubyでgRPCアプリケーションの開発をしていると、コードを変更した際にサーバを再起動せずに コードの変更を反映する方法です。

定数の再読込にZeitwerkを使い、コードの変更の検知にfilewatcherを使っていますが、 それぞれ同等の課題解決をするgemで置き換えは可能です。

環境

使用しているGemとバージョン

TODO: (あとでリンクはる)

  • grpc (1.31.1)
  • zeitwerk (2.4.0)
  • filewatcher (1.1.1)

Rubyは2.7.1です。

最後のfilewatcherはファイルの変更を検知できるGemなら代替できます。 代表的なものとしてはRailsでも使用されているlistenなどがありますね。

guard/listen - GitHub

filewatcherを選んだ理由としては、listenと比較してコード量と依存関係が小さかったためです。

Zeitwerkを使った理由は、

  • Railsでの開発に慣れすぎていて、 require_relative を書きまくるのがつらかった

    • zeitwerkのオートロードで解決
  • 定数の再読み込みがほしかった

の2つの課題を解決できる、1粒で2度美味しいソリューションだったからです。

実装方法

まずはコードの全貌です。

class ApplicationServer
  include Singleton

  def self.prepare_server
    server = GRPC::RpcServer.new
    server_location = "0.0.0.0:#{Env.grpc_port}"
    server.add_http2_port(server_location, :this_port_is_insecure)
    Env.logger.info "server starting: #{server_location}"
    server.handle(BeersServer)
    server.handle(UsersServer)
    server.handle(PinsServer)

    server
  end

  def serve
    @grpc_servers ||= []
    @threads ||= []
    r, w = IO.pipe
    @threads << Thread.new do
      if (msg = r.gets)
        Env.logger.debug "received! msg: #{msg}"
        @grpc_servers.each { |s| s.stop }
      end
    end
    Signal.trap(:INT) do
      w.puts "trapped"
    end

    start_on_background
    @threads.each(&:join)
  end

  def restart
    unless @grpc_servers.empty?
      @grpc_servers.each { |s| s.stop }
      @grpc_servers = []
      unless port_free?("0.0.0.0", Env.grpc_port)
        Env.logger.debug "waiting..."
        sleep 1
      end
      start_on_background
    end
  end

  private

  def start_on_background
    server = self.class.prepare_server
    @grpc_servers << server
    @threads << Thread.new do
      server.run
    end
    Env.logger.info "server started"
  end

  def port_free?(ip, port)
    s = Socket.tcp(ip, port, connect_timeout: 5)
    s.close
  rescue Errno::ECONNREFUSED => e
    Env.logger.debug "#{e.class}: #{e.message}"
    return true
  rescue => e
    Env.logger.debug "#{e.class}: #{e.message}"
    return false
  end

end

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# Ruby # gRPC
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