nginx 集群系列

本节描述如何使用NGINX和NGINX服务静态内容,搜索的方法来定义路径找到所请求的文件,以及如何建立索引文件。

本文重点：

• 根目录和索引文件
• 服务选项
• 优化NGINX速度为内容服务

根目录和索引文件

root指令指定根目录,用于寻找一个文件。To obtain the path of a requested file, NGINX appends the request URI to the path specified by the root directive. The directive can be placed on any level within the http, server, or location contexts. In the example below, the root directive is defined for a virtual server. It applies to all location blocks where the root directive is not included to explicitly redefine the root(它可以应用在所有root没有被显示定义的location):

server {    root /www/data;    location / {    }    location /images/ {    }    location ~ \.(mp3|mp4) {        root /www/media;    }}

Here, NGINX searches for a URI that starts with /images/ in the /www/data/images/ directory on the file system. But if the URI ends with the .mp3 or .mp4 extension, NGINX instead searches for the file in the /www/media/ directory because it is defined in the matching location block.

If a request ends with a slash, NGINX treats it as a request for a directory and tries to find an index file in the directory. The index directive defines the index file’s name (the default value is index.html). To continue with the example, if the request URI is /images/some/path/, NGINX delivers the file /www/data/images/some/path/index.html if it exists. If it does not, NGINX returns HTTP code 404 (Not found) by default. To configure NGINX to return an automatically generated directory listing instead, include the on parameter to the autoindex directive:

location /images/ {    autoindex on;}

You can list more than one filename in the index directive. NGINX searches for files in the specified order and returns the first one it finds.

location / {    index index.$geo.html index.htm index.html;}

The $geo variable used here here is a custom variable set through the geo directive. The value of the variable depends on the client’s IP address.

To return the index file, NGINX checks for its existence and then makes an internal redirect to the URI obtained by appending the name of the index file to the base URI. The internal redirect results in a new search of a location and can end up in another location as in the following example:

location / {    root /data;    index index.html index.php;}location ~ \.php {    fastcgi_pass localhost:8000;    ...}

Here, if the URI in a request is /path/, and /data/path/index.html does not exist but /data/path/index.php does, the internal redirect to /path/index.php is mapped to the second location. As a result, the request is proxied.

服务选项

The try_files directive can be used to check whether the specified file or directory exists and make an internal redirect, or return a specific status code if they don’t. For example, to check the existence of a file corresponding to the request URI, use the try_files directive and the $uri variable as follows:

server {    root /www/data;    location /images/ {        try_files $uri /images/default.gif;    }}

The file is specified in the form of the URI, which is processed using the root or alias directives set in the context of the current location or virtual server. In this case, if the file corresponding to the original URI doesn’t exist, NGINX makes an internal redirect to the URI specified in the last parameter, returning /www/data/images/default.gif.

The last parameter can also be a status code (directly preceded by the equals sign) or the name of a location. In the following example, a 404 error is returned if none of the parameters to the try_files directive resolve to an existing file or directory.

location / {    try_files $uri $uri/ $uri.html =404;}

In the next example, if neither the original URI nor the URI with the appended trailing slash resolve into an existing file or directory, the request is redirected to the named location which passes it to a proxied server.

location / {    try_files $uri $uri/ @backend;}location @backend {    proxy_pass http://backend.example.com;}

For more information, watch the Content Caching on-demand webinar to learn how to dramatically improve the performance of a website, and get a deep-dive into NGINX’s caching capabilities.

优化NGINX速度为内容服务

Loading speed is a crucial factor of serving any content. Making minor optimizations to your NGINX configuration may boost the productivity and help reach optimal performance.

Enabling sendfile

By default, NGINX handles file transmission itself and copies the file into the buffer before sending it. Enabling the sendfile directive will eliminate the step of copying the data into the buffer and enables direct copying data from one file descriptor to another. Alternatively, to prevent one fast connection to entirely occupy the worker process, you can limit the amount of data transferred in a single sendfile() call by defining the sendfile_max_chunk directive:

location /mp3 {    sendfile           on;    sendfile_max_chunk 1m;    ...}

Enabling tcp_nopush

Use the tcp_nopush option together with sendfile on;. The option will enable NGINX to send HTTP response headers in one packet right after the chunk of data has been obtained by sendfile

location /mp3 {    sendfile   on;    tcp_nopush on;    ...}

Enabling tcp_nodelay

The tcp_nodelay option allows overriding the Nagle’s algorithm, originally designed to solve problems with small packets in slow networks. The algorithm consolidates a number of small packets into the larger one and sends the packet with the 200 ms delay. Nowadays, when serving large static files, the data can be sent immediately regardless of the packet size. The delay would also affect online applications (ssh, online games, online trading). By default, the tcp_nodelay directive is set to on which means that the Nagle’s algorithm is disabled. The option is used only for keepalive connections:

location /mp3  {    tcp_nodelay       on;    keepalive_timeout 65;    ...}

Optimizing the Backlog Queue

One of the important factors is how fast NGINX can handle incoming connections. The general rule is when a connection is established, it is put into the “listen” queue of a listen socket. Under normal load, there is either low queue, or there is no queue at all. But under high load, the queue may dramatically grow which may result in uneven performance, connections dropping, and latency.

Measuring the Listen Queue

Let’s measure the current listen queue. Run the command:

netstat -Lan
The command output may be the following:

Current listen queue sizes (qlen/incqlen/maxqlen)Listen         Local Address         0/0/128        *.12345            10/0/128        *.80       0/0/128        *.8080

The command output shows that there are 10 unaccepted connections in the listen queue on Port 80, while the connection limit is 128 connections, and this situation is normal.

However, the command output may be as follows:

Current listen queue sizes (qlen/incqlen/maxqlen)Listen         Local Address         0/0/128        *.12345            192/0/128        *.80       0/0/128        *.8080

The command output shows 192 unaccepted connections which exceeds the limit of 128 connections. This is quite common when a web site experience heavy traffic. To achieve optimal performance you will need to increase the maximum number of connections that can be queued for acceptance by NGINX in both your operating system and NGINX configuration.

Tuning the Operating System

Increase the value of the net.core.somaxconn key from its default value (128) to the value high enough to be able to handle a high burst of traffic:

For FreeBSD, run the command:sudo sysctl kern.ipc.somaxconn=4096For Linux, run the command:sudo sysctl -w net.core.somaxconn=4096Open the file: /etc/sysctl.confvi   /etc/sysctl.conf

Add the line to the file and save the file:

net.core.somaxconn = 4096

Tuning NGINX

If you set the somaxconn key to a value greater than 512, change the backlog parameter of the NGINX listen directive to match:

server {    listen 80 backlog=4096;    # The rest of server configuration}