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How to implement an HTTP output filter in nginx

Internally nginx HTTP server has a stack of output filters. These filters affect the reply generated by other sources, such as phase handlers or upstream. There are 2 types of output filter: header filters and body filters. Obviously, header filters apply to the header of the reply and body filters apply to the body of […]

Getting cookie value in nginx

nginx allows you to extremely easily extract the value of a cookie. Simply use $cookie_<name> meta variable in whatever context you need. Here is an example: location / { proxy_set_header X-Session-id $cookie_sid; proxy_pass http://upstream; } In this configuration snippet we pass the request to the upstream named “upstream” and extend it with a header “X-Session-id” […]

Nginx Essentials is available for pre-order

Nginx Essentials is available for pre-order! This is my first book ever and my first book about Nginx. The book is conceived as “programmer’s view of Nginx administration” and intends to enrich web masters’ and site reliability engineers’ knowledge with subtleties known to those who have deep understanding of Nginx core. At the same time, […]

Logging modules re-released!

Few months ago I shut down the pages of nginx socketlog module and nginx redislog module. This is due to excessive volume of support they required. Some people, however, found that these are interesting pieces of technology and I got several requests to release them. Today I release these modules under free licence. Meet the […]

Counting unique visitors

In version 1.0.2 of redislog module I added a feature that allows you to do conditional logging. What can you do with it? For example, logging only unique visitors. E.g.: userid on; userid_name uid; userid_expires 365d; access_redislog test “$server_name$redislog_yyyymmdd” ifnot=$uid_got; $uid_got becomes empty whenever a visitor doesn’t have an UID cookie. Therefore, this directive effectively […]

Better logging for nginx

Somehow the problem of logging was not completely addressed in nginx. I managed to implement 2 solutions for remote logging: nginx socketlog module and nginx redislog module. Each of these modules maintain one permanent connection per worker to logging peer (BSD syslog server or redis database server). Messages are buffered in 200k buffer even when […]

Configuration directives

In one of the previous articles I discussed the basics of HTTP modules. As the power of Nginx comes from configuration files, you definitely need to know how to configure your module and make it ready for variety of environments that users of your module can have. Here is how you can define configuration directives.

Measuring time spent on page

One of the challenges of A/B testing is insufficient observations due to low traffic. In other words, if you measured the conversion rate on our web site, it would take months or even years before we’d get conclusive result. What you can try to measure are microconversion and microobservations. That’s what I was up to […]

An HTTP module basics and configuration

In the previous article I explained how modules of all types link into Nginx. Now let’s  look closer at the specifics of HTTP modules. An HTTP module has the value NGX_HTTP_MODULE in its type field and the ctx field points to a global instance of a structure ngx_http_module_t:

How your module plugs into Nginx

In previous articles I have deliberately omitted almost everything related to the question of linking your module with Nginx. It is important, however, that you know about it. Let’s take a closer look at the metainformation that your module must contain, so that Nginx can initialise and configure it.

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