App Server Scaling - Web Development Udacity Japanese English

App Server Scaling - Web DevelopmentYouTube↗ IA↗(long shot)
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データベースの負荷を軽くする方法を見てきました

Okay so uh,we've taking a fair amount of load off our

実際にソリューションを検討する際に

database. Now if we were to go through that whole solution,

データベースの書き込みのみに集中して

we'd only be doing database right and we'd very rarely be

読み込みは最低限にすると

doing a database read at all. And this is a big improvement

閲覧ごとに読み込むより動作が大幅に改善します

over doing a database read on every page view. So let's

リクエストの処理の手順は

go back to what our request does. And every request remember

まずリクエストはHTTPやURLなどを通して処理されます

we, we process the request. You know, this was HTTP, URLs

そしてデータベースクエリをします

and all that stuff. We did the DB query, the database query.

次は結果の照合です　ただASCII Chanに関しては

We collated the results, which for you know, ASCII Chan

まったく考慮しなくて大丈夫です

or the blog is, there's not really much involved in

そしてそれからHTMLをレンダリングします

that at all. And then, we rendered the HTML. So,

データベースクエリは改善済みですが

we've improved the database query, but what if we want to improve

他についてはどうでしょうか?

these other, other pieces. Yeah, we can use caching to

キャッシュはHTMLのレンダリングに有効ですが

render HTML. That's definitely a technique there, and we can actually

3つの処理すべてに効果的なワザがあります

use another technique for handling all three of these parts

今から紹介するアプリケーションサービスを追加するのです

of the requests, which is adding additional app service and this

仮に1つのプログラムを実行し

looks something like this. To date conceptually we've basically had

ブログやASCII Chanなどすべてのリクエストを

one program running, that handles all of our requests in

処理しているとします

your blog and an ASCII Chan. We've got the simple

現状はシンプルなリクエストを処理できる状態ですが

program you know, requests come in. Responses come back out, but

マシン1台では対応できない大量のリクエストが来た場合は

if so many requests that one machine can't handle it.

マシンを増設して

We can do is we can add multiple machines, to take

負荷を分散するのもひとつの方法です

up some of the load. So all of these extra

そうすれば処理を他のマシンに振り分けたり

requests can go to all of these machines, and these machines

マシン同士をデータベースで連結させることも可能かもしれません

maybe interacting with the database. They may not be. Presumably

その際それぞれのマシンのシステムで

they have their little caches that we just implemented that

キャッシュできればなお便利でしょう

lives in our program and, and this helps so how

ではどうやって複数のマシンでリクエストを処理するのでしょう

do we get requests to multiple machines. Well, there's a piece

そこでユーザとすべてのサーバの間に

of technology that sits between the user and all of

ロードバランサと呼ばれるものを置きます

your app servers called a load balancer. And this is

ロードバランサは APサーバやデータベースサーバのように

a special machine, it's a physical machine just like your

物理的な装置です

app server might be or just like your database server might

ロードバランサの唯一の用途は

be, that's optimized for doing one this, for spreading

リクエストを複数のマシンに分散することです

requests across multiple machines. So, what happens is, this load

ロードバランサには

balancer has a list of all of the app servers

実在するAPサーバのリストがあり

that, that are in existence, and requests come in from

大量のリクエストを外部から受けると

the outside world, many, many, many of them. And the

どのAPサーバにリクエストを送るか決めます

load balancer decides which app server to send the request

これはこここれはここといった具合に

to. Send one here, then send one here. Then send

振り分けていきます

one here. And it can keep going to that process.

APサーバと違ってロードバランサに

And the reason this load balancer can handle all this

このような処理ができる理由は

traffic while the app servers can't, is the low balancer isn't

リクエストの受け取りやサーバの選択

doing anything other than taking in the request, choosing a server,

コネクションの転送だけを行うからです

and forwarding the connection along. It doesn't have to parse HTTP

HTTPの解析はほとんど行いませんし

or it may only parse, parse minimal HTTP. It doesn't have

データベースクエリも実行しません

to, it's not doing database queries, it's not rendering HTML, it's

HTMLのレンダリングもキャッシュもしません唯一と言える役割は

not, going to the cache it's, it's doing almost nothing at

リクエストの振り分けだけなのです

all, other than deciding which server to send a request to.

皆さんが自分で作成することはないと思いますが

You've probably won't ever have to write one of these, but it's

仕組みを知ることは有益です

good to know how they work. And when you're using App Engine,

Google App Engineを利用していれば

Google kind of does all of this for you. They'll automatically create new

サーバの作成やスケーリングを自動でしてくれます

servers running your program and and scale. You can actually go into the

GAEの管理画面で自分のWebアプリケーションをホストするための

app engine admin page and see how many servers they are using

サーバの数を確認できます

to host your app. Which is pretty cool. Normally this is a

ロードバランサの設置は簡単ではありません

really challenging thing, and not knowing how to do it the first

私もRedditをスケーリングする際に

time, this took me a little while to figure out when we were

時間がかかりました　ここでしっかり学びましょう

scaling Reddit. That doesn't mean I'm not going to make you understand these

ロードバランサがトラフィックを

things a little bit deeper. So, there are a couple algorithms a

どのサーバに送るか決めるアルゴリズムがあります

load balancer can use to determine which server to send traffic to.

最も簡単な方法はランダムにサーバを選ぶことです

The simplest one is probably just to randomly choose a server. Now,

リクエストを受け取ると

a request comes into the load balancer and the load balancer just

ロードバランサが無作為にサーバを選びリクエストを送ります

picks a server and sends a request there which will, you know,

この場合多くのリクエストが出されると

probably work pretty well. You know, over, over time, if you have

各サーバの負荷は同じになるはずです

enough requests, each server should get about the same amount of load.

他の方法としてラウンドロビンがあります

Other approach is round robin, and round robin just means a load

これはロードバランサが順番にサーバを選ぶ方法です

balancer will choose one server at the time. You know, first this guy,

最初はこれ次はこれというように選びます

then this guy, then this guy, then this guy, you know, just,

非常にシンプルなアルゴリズムです

in order. That's also a fairly simple algorithm. And then some of the

ロードバランサの中には各サーバの負荷や

balances are really smart and they know what the load is on

未処理のリクエスト数を把握していてその情報によって

each server, how many requests are outstanding at each server, and it may

リクエストを振り分けるものもあります

use some sort of load based algorithm just so you know. This guy's

"これはすでに5個も抱えているがこちらはゼロなので"

already handling like five requests and this guy's not doing anything so let's

"次はこちらに"という要領です

send, you know, future requests here until, you know, things

このように負荷分散には様々な方法があります

even out. There's lots of approaches to doing this. What

ではここで小クイズです

I'm going to ask you to do now in the form

ラウンドロビンアルゴリズムの実装についてです

of a quiz is implement a basic round robin algorithm.

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