Book Image

Nginx HTTP Server, Third Edition

By : Clement Nedelcu
Book Image

Nginx HTTP Server, Third Edition

By: Clement Nedelcu

Overview of this book

Nginx is a lightweight HTTP server designed for high-traffic websites, with network scalability as the primary objective. With the advent of high speed Internet access, short loading times and fast transfer rates have become a necessity. This free, open source solution will either come as a full replacement of other software such as Apache, or stand in front of your existing infrastructure to improve its overall speed. This book is a detailed guide to setting up Nginx in different ways that correspond to actual production situations: as a standalone server, as a reverse proxy, interacting with applications via FastCGI, and more. In addition, this complete directive reference will be your best friend at all stages of the configuration and maintenance processes. This book is the perfect companion for both Nginx beginners and experienced administrators. For beginners, it will take you through the complete process of setting up this lightweight HTTP server on your system and configuring its various modules so it does exactly what you need quickly and securely. For more experienced administrators, this book provides different approaches that can help you make the most of your current infrastructure. Nginx can be employed in many situations, whether you are looking to construct an entirely new web-serving architecture or simply want to integrate an efficient tool to optimize your site loading speeds.
Table of Contents (17 chapters)
Nginx HTTP Server Third Edition
About the Author
About the Reviewer

Controlling the Nginx service

At this stage, you should have successfully built and installed Nginx. The default location for the output files is /usr/local/nginx, so we will be basing future examples on this.

Daemons and services

The next step is obviously run Nginx for the first time. However, before doing so, it's important to understand the nature of this application. There are two types of computer applications—those that require immediate user input, thus running in the foreground, and those that do not, thus running in the background. Nginx is of the latter type, often referred to as daemon. Daemon names usually come with a trailing "d" and a couple of examples can be mentioned here—httpd, the HTTP server daemon, is the name given to Apache under several Linux distributions; named, the name server daemon; or crond the task scheduler—although, as you will notice, this is not the case for Nginx. When started from the command line, a daemon immediately returns the prompt, and in most cases, does not even bother outputting data to the terminal.

Consequently, when starting Nginx, you will not see any text appear on the screen, and the prompt will return immediately. While this might seem startling, it is, on the contrary, a good sign. It means the daemon was started correctly and the configuration did not contain any errors.

User and group

It is of utmost importance to understand the process architecture of Nginx, and particularly the user and groups under which its various processes run. A very common source of trouble when setting up Nginx is invalid file access permissions—due to a user or group misconfiguration, you often end up getting 403 Forbidden HTTP errors because Nginx cannot access the requested files.

There are two levels of processes with possibly different permission sets:

  • The Nginx master process: This should be started as root. In most Unix-like systems, processes started with the root account are allowed to open TCP sockets on any port, whereas other users can only open listening sockets on a port above 1024. If you do not start Nginx as root, standard ports such as 80 or 443 will not be accessible. Note that the user directive that allows you to specify a different user and group for the worker processes will not be taken into consideration for the master process.

  • The Nginx worker processes: These are automatically spawned by the master process under the account you specified in the configuration file with the user directive (detailed in Chapter 2, Basic Nginx Configuration). The configuration setting takes precedence over the configuration switch you may have specified at compile time. If you did not specify any of those, the worker processes will be started as user nobody and group nobody (or nogroup depending on your OS).

Nginx command-line switches

The Nginx binary accepts command-line arguments to perform various operations, among which is controlling the background processes. To get the full list of commands, you may invoke the help screen using the following commands:

[[email protected] ~]$ cd /usr/local/nginx/sbin
[[email protected] sbin]$ ./nginx -h

The next few sections will describe the purpose of these switches. Some allow you to control the daemon and some let you perform various operations on the application configuration.

Starting and stopping the daemon

You can start Nginx by running the Nginx binary without any switches. If the daemon is already running, a message will show up indicating that a socket is already listening on the specified port:

[emerg]: bind() to failed (98: Address already in use) […] [emerg]: still could not bind().

Beyond this point, you may control the daemon by stopping it, restarting it, or simply reloading its configuration. Controlling is done by sending signals to the process using the nginx -s command.



nginx –s stop

Stops the daemon immediately (using the TERM signal).

nginx –s quit

Stops the daemon gracefully (using the QUIT signal).

nginx –s reopen

Reopens the log files.

nginx –s reload

Reloads the configuration.

Note that when starting the daemon, stopping it, or performing any of the preceding operations, the configuration file is first parsed and verified. If the configuration is invalid, whatever command you have submitted will fail, even when trying to stop the daemon. In other words, in some cases you will not be able to even stop Nginx if the configuration file is invalid.

An alternate way to terminate the process, in desperate cases only, is to use the kill or killall commands with root privileges:

[[email protected] ~]# killall nginx

Testing the configuration

As you can imagine, testing the validity of your configuration will become crucial if you constantly tweak your server setup . The slightest mistake in any of the configuration files can result in a loss of control over the service—you will then be unable to stop it via regular init control commands, and obviously, it will refuse to start again.

Consequently, the following command will be useful to you in many occasions; it allows you to check the syntax, validity, and integrity of your configuration:

[[email protected] ~]$ /usr/local/nginx/sbin/nginx –t

The –t switch stands for test configuration. Nginx will parse the configuration anew and let you know whether it is valid or not. A valid configuration file does not necessarily mean Nginx will start, though, as there might be additional problems such as socket issues, invalid paths, or incorrect access permissions.

Obviously, manipulating your configuration files while your server is in production is a dangerous thing to do and should be avoided when possible. The best practice, in this case, is to place your new configuration into a separate temporary file and run the test on that file. Nginx makes it possible by offering the –c switch:

[[email protected] sbin]$ ./nginx –t –c /home/alex/test.conf

This command will parse /home/alex/test.conf and make sure it is a valid Nginx configuration file. When you are done, after making sure that your new file is valid, proceed to replacing your current configuration file and reload the server configuration:

[[email protected] sbin]$ cp -i /home/alex/test.conf /usr/local/nginx/conf/nginx.conf
cp: erase 'nginx.conf' ? yes
[[email protected] sbin]$ ./nginx –s reload

Other switches

Another switch that might come in handy in many situations is –V. Not only does it tell you the current Nginx build version, but more importantly, it also reminds you about the arguments that you used during the configuration step—in other words, the command switches that you passed to the configure script before compilation.

[[email protected] sbin]$ ./nginx -V
nginx version: nginx/1.8.0 (Ubuntu)
built by gcc 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04)
TLS SNI support enabled
configure arguments: --with-http_ssl_module

In this case, Nginx was configured with the --with-http_ssl_module switch only.

Why is this so important? Well, if you ever try to use a module that was not included with the configure script during the precompilation process, the directive enabling the module will result in a configuration error. Your first reaction will be to wonder where the syntax error comes from. Your second reaction will be to wonder if you even built the module in the first place! Running nginx –V will answer this question.

Additionally, the –g option lets you specify additional configuration directives in case they were not included in the configuration file:

[[email protected] sbin]$ ./nginx –g "timer_resolution 200ms";