WebSockets & Realtime Systems Programming · レッスン

WebSocketのロードバランシング

ロードバランサー（例：Nginx、HAProxy）を設定し、スティッキーセッションとWebSocketへのアップグレードを正しく処理します。

「WebSocketのロードバランシング」はCoddyKit上の無料WebSockets & Realtime Systems Programmingレッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはWebSockets & Realtime Systems Programming学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 WebSockets & Realtime Systems Programmingコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Scaling WebSockets with Load Balancers

When your WebSocket application grows, a single server might not handle all connections efficiently. Load balancing helps by distributing these connections across multiple servers.

This improves performance, reliability, and allows your application to handle more users. It's a crucial step for high-traffic realtime systems to ensure availability and responsiveness.

The WebSocket Handshake

Unlike regular HTTP connections, WebSockets begin with a special "handshake" process that uses HTTP. Your client sends an initial HTTP request to the server, asking to "upgrade" the connection.

This request includes specific HTTP headers that signal the intent to switch protocols. If the server agrees, it responds with an HTTP 101 Switching Protocols status, and the connection then becomes a full-duplex WebSocket.

Load Balancers & Upgrade Headers

A standard HTTP load balancer might not correctly process the WebSocket upgrade request. It needs specific configuration to properly forward the special HTTP headers essential for the handshake. These headers include:

Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Key
Sec-WebSocket-Version

Without proper forwarding, the WebSocket handshake will fail, preventing the connection from establishing.

Sticky Sessions: Essential for WebSockets

Once a WebSocket connection is established, it's persistent. It's often critical that all subsequent messages from a client go to the same backend server that handled the initial handshake and established the connection.

This is known as a "sticky session" or "session persistence." If a client's messages are routed to a different server, the connection will break or behave unexpectedly, as the new server won't recognize the existing WebSocket session.

How Sticky Sessions Work

Load balancers use different methods to ensure sticky sessions:

IP Hash: The load balancer uses the client's IP address to consistently route them to the same backend server. This is simple but less effective if many users share an IP (e.g., behind a NAT).
Cookie-Based: The load balancer sets a special cookie in the client's browser. Subsequent requests include this cookie, allowing the load balancer to route them to the correct server. This method is generally more robust.

Nginx: Proxying WebSocket Upgrades

Nginx is a popular, high-performance web server that also excels as a reverse proxy and load balancer. To handle WebSockets, Nginx needs configuration to correctly forward the upgrade headers, ensuring the initial HTTP handshake completes successfully.

The proxy_set_header directives for Upgrade and Connection are crucial. Also, a long proxy_read_timeout is recommended for persistent WebSocket connections.

http {
    upstream websocket_backend {
        server backend1.example.com;
        server backend2.example.com;
    }

    server {
        listen 80;
        server_name example.com;

        location /ws/ {
            proxy_pass http://websocket_backend;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";
            proxy_read_timeout 86400s; # Long timeout for WebSockets
        }
    }
}

Nginx: Implementing Sticky Sessions

To ensure sticky sessions with Nginx, you can use the ip_hash directive in your upstream block. This directive ensures that requests from the same client IP address are consistently routed to the same backend server.

While straightforward, remember that IP hash might not be ideal for all scenarios, especially when multiple users share a single public IP address.

http {
    upstream websocket_backend {
        ip_hash; # Enables sticky sessions by client IP
        server backend1.example.com;
        server backend2.example.com;
    }

    server {
        listen 80;
        server_name example.com;

        location /ws/ {
            proxy_pass http://websocket_backend;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";
            proxy_read_timeout 86400s;
        }
    }
}

HAProxy: Basic WebSocket Configuration

HAProxy is another powerful and widely used open-source load balancer, especially known for its high availability and advanced routing capabilities. Configuring HAProxy for WebSockets involves setting the correct operating mode (mode http) and creating rules to identify and route WebSocket traffic.

An Access Control List (ACL) is often used to detect the Upgrade: websocket header and direct traffic to a specific backend server pool.

frontend http_front
    bind *:80
    mode http
    default_backend ws_backend

backend ws_backend
    mode http
    option http-server-close
    acl is_websocket hdr(Upgrade) -i websocket
    use_backend ws_servers if is_websocket
    default-server inter 1s fall 2 rise 5

backend ws_servers
    mode http
    balance roundrobin
    server web1 192.168.1.1:8000 check
    server web2 192.168.1.2:8000 check

HAProxy: Cookie-Based Sticky Sessions

For more robust sticky sessions, HAProxy can insert a cookie into the client's browser that identifies the specific backend server the client is connected to. The client then sends this cookie with all subsequent requests, ensuring they are consistently routed to the same server.

This method provides better stickiness than IP hash, especially in environments where client IPs might change or be shared.

backend ws_servers
    mode http
    balance roundrobin
    cookie SERVERID insert indirect nocache # Insert a cookie
    server web1 192.168.1.1:8000 check cookie s1
    server web2 192.168.1.2:8000 check cookie s2

Check Your Understanding

Which of the following are essential considerations when configuring a load balancer for WebSocket traffic?

Load Balancing WebSockets Recap

In this lesson, we explored the critical aspects of load balancing WebSocket applications:

WebSockets initiate with an HTTP upgrade handshake, requiring specific headers to be properly forwarded by the load balancer.
Sticky sessions are vital to ensure a client maintains its persistent connection with the same backend server throughout its lifecycle.
Load balancers like Nginx and HAProxy can be configured to handle WebSocket upgrades and implement sticky sessions using methods such as IP hash or cookie-based routing.

Mastering these configurations is key to building scalable, resilient, and high-performance realtime systems.

よくある質問

「WebSocketのロードバランシング」レッスンは無料ですか？

はい。「WebSocketのロードバランシング」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、WebSockets & Realtime Systems Programmingコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 WebSockets & Realtime Systems Programmingコースには全4レッスンが含まれています。

「WebSocketのロードバランシング」で何を学びますか？

ロードバランサー（例：Nginx、HAProxy）を設定し、スティッキーセッションとWebSocketへのアップグレードを正しく処理します。ブラウザで直接実行するハンズオンコードでWebSockets & Realtime Systems Programmingを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

WebSockets & Realtime Systems Programmingを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのWebSockets & Realtime Systems Programmingは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「WebSocketのロードバランシング」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このWebSockets & Realtime Systems Programmingレッスンでコードを書いて実行できますか？

はい。すべてのWebSockets & Realtime Systems Programmingレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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