啟用客戶端和上游Keepalive連接可顯著提升Nginx性能；2. 客戶端側(cè)設(shè)置keepalive_timeout和keepalive_requests以控制空閑時間和請求上限；3. 上游側(cè)需在upstream塊中配置keepalive數(shù)量并使用proxy_http_version 1.1與proxy_set_header Connection ""實(shí)現(xiàn)連接復(fù)用；4. 錯誤配置會導(dǎo)致連接無法復(fù)用或資源耗盡，正確調(diào)優(yōu)可降低延遲20–50%并減少CPU開銷。

When optimizing web server performance—especially with Nginx—Keepalive connections are one of the most impactful settings you can tune. They reduce latency, lower CPU overhead from TCP handshakes, and improve overall throughput for both clients and upstream servers.

Here’s what you need to know:

? What Are Keepalive Connections?

Keepalive keeps a TCP connection open after a request/response cycle so that multiple HTTP requests can be sent over the same connection instead of opening a new one each time. This avoids the overhead of repeated TCP and TLS handshakes.

In Nginx, there are two main contexts where keepalive matters:

1. Client → Nginx (browser to server)
2. Nginx → Upstream (like app servers or backends)

? Client-side Keepalive (Browser to Nginx)

This is handled automatically if the client supports HTTP/1.1 (which it almost always does). But you can fine-tune it in your server block:

server {
    keepalive_timeout  65s;     # How long to keep idle client connections open
    keepalive_requests 100;     # Max requests per connection (default 100)
}

• keepalive_timeout: If no new request comes within this time, the connection closes.
• keepalive_requests: Limits how many requests one connection can serve—useful to prevent memory leaks or resource exhaustion.

? Tip: For high-traffic sites, lowering keepalive_timeout to 15–30s can reduce idle connections without hurting performance much.

?? Upstream Keepalive (Nginx to Backend)

This is where many miss big performance gains. If Nginx proxies to a backend (e.g., FastAPI, Node.js, PHP-FPM), enabling keepalive there reduces latency dramatically.

Step 1: Define an upstream with keepalive pool

upstream backend {
    server 127.0.0.1:8000;
    keepalive 32;  # Number of idle keepalive connections per worker
}

Step 2: Configure the proxy to reuse connections

location / {
    proxy_pass http://backend;
    proxy_http_version 1.1;
    proxy_set_header Connection "";
}

Why these lines?

• proxy_http_version 1.1; — Required for keepalive (HTTP/1.0 doesn’t support it).
• proxy_set_header Connection ""; — Clears the Connection: close header from the client, allowing Nginx to reuse the upstream connection.

Without this, every proxy request opens a new TCP connection to your backend—wasteful and slow.

? Real-World Impact

• Latency: Eliminates TCP/TLS handshake per request → faster response times.
• Throughput: One connection can handle dozens or hundreds of requests.
• CPU/Memory: Fewer connections = less overhead on both Nginx and upstream servers.

For example, if your backend is a Python app behind Gunicorn, enabling upstream keepalive in Nginx can reduce average response time by 20–50% under load.

? Common Pitfalls

• Forgetting proxy_set_header Connection ""; — upstream connections won’t be reused.
• Not setting keepalive in upstream block — defaults to no keepalive.
• Too high a keepalive_timeout — can exhaust file descriptors on busy servers.
• Using HTTP/1.0 in proxy — won’t support keepalive at all.

Basically, if you're using Nginx as a reverse proxy (which most people are), enabling both client and upstream keepalive is low-hanging fruit for better performance. It’s not magic—it’s just smart reuse of connections.

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