Server_name指令做什麼？

Nginx中的server_name指令用於根據客戶端發送的Host頭選擇處理請求的虛擬主機。具體來說：1. server_name通過精確匹配、通配符或正則表達式匹配Host頭，決定使用哪個server塊；2. 未匹配時會回退到默認server塊，通常是第一個或顯式標記為default_server的塊；3. 正確配置server_name有助於避免內容重複、提升SEO並增強性能；4. 複雜匹配和通配符應謹慎使用，以保持清晰性和效率。因此，合理設置server_name能確保流量正確路由並簡化服務器維護。

The server_name directive in Nginx is used to determine which virtual host (or server block) should handle an incoming HTTP request based on the "Host" header sent by the client.

How It Helps Route Traffic

When a browser makes a request, it includes a Host header that tells the server which domain name it's trying to reach. Nginx uses this information along with the server_name directive to decide which website configuration to use.

For example, if you're hosting both example.com and testsite.com , each site will have its own server block with a different server_name . That way, Nginx knows exactly which files or services to serve for each domain.

Some things to note:

• You can match exact names: server_name example.com;
• You can use wildcards: server_name *.example.com;
• You can also use regular expressions if needed: server_name ~^www\d \.example\.com$;

Default Server Block Behavior

If no server_name matches the Host header, Nginx falls back to the default server. This is usually the first server block unless explicitly set using the listen directive like listen 80 default_server; .

This behavior matters because:

• It prevents unexpected content from being served when domains don't match
• It helps avoid SEO issues where duplicate content might appear under multiple domain names

So, setting up a fallback server that returns an error (like 444 or 404) is often a good idea if there's no intended use for unmatched requests.

Performance and SEO Considerations

Using server_name correctly isn't just about routing — it affects performance and SEO too. For instance:

• Misconfigured server_name entries may lead to duplicate content across domains
• Using unnecessary regex or complex matching when not needed can add overhead
• Wildcard subdomains are useful but should be used with care for clarity and speed

A clean setup with clear domain separation makes maintenance easier and reduces chances of conflicts as your server scales.

In short, server_name is how Nginx chooses the right config for each domain. Use it clearly, keep it simple unless complexity is needed, and always test changes.基本上就這些。

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