May 2019
Intermediate to advanced
464 pages
9h 22m
Japanese
Content preview from Node.jsデザインパターン 第2版
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10.3
複雑なアプリケーションの分解
369
ケストレータは「ゴッドオブジェクト」と呼ばれるアンチパターンになります。これは、知っていること
も行うことも多すぎるオブジェクトを指す言葉で、結合度が高くなり、凝集度が低くなり、もっとも重
要なこととして複雑になってしまうのが普通です。
これから示すパターンは、システム全体の情報の同期の責任を、サービス間に分散させようとする
ものです。しかし、サービス間に直接の関係を作ってしまうと、ノード間の相互接続の数が増加するこ
とにより、結合度が上昇しシステムの複雑性がさらに増加しますから、それは何としても避けたいとこ
ろです。目標は各サービスが隔離状態を維持することで、システムの他のサービスがなくても、あるい
は新たなサービスやノードと組み合わさっても、各サービスが動作できるようになることです。
解決策はメッセージブローカを使うことです。これはメッセージの送信者と受信者を分
離する能力
をもったシステムで、集中化したパブリッシュ
/
サブスクライブ（
pub/sub
）パターンの実装を可能にし、
事実上は分散システムのためのオブザーバパターンです（このパターンについては後のほうでさらに説
明します）。図10-14は電子商取引アプリケーションにこれがどのように当てはめられるかを示していま
す。
「製品」用サービス「カート」用サービス「チェックアウト」用
サービス
ストアのフロントエンド用アプリ
ストアのフロントエンド
チェックアウト カート 製品
メッセージブローカ
(2){
event:
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.