How to write only logs with 200 status

Question

I'm trying to figure out how to do the following:

1. Request is coming in.

2. HttpLuaModule performs some action against the request. If request is valid than Lua will finish processing with ngx.exit(202). But there are some conditions that may (and will) occur during the processing and nginx might return 403 , 404, 503 Errors.

What I want to do is to write to access logs only requests that have 200 Status code. Basically I would like to do something like this:

location /foo {
    content_by_lua_file "/opt/nginx/lua/process.lua";
    if (status == 200) {
        access_log "/path/to/the/access_log"
    } 

I'm very new to both nginx and lua so for me it's a bit of a challenge to figure out where to place and if statement (ether after content_by_lua_file or in side lua file) and what this if statement should look like.

Answer 1

nginx 1.7.0+ allows using an if condition in access_log directive itself.

access_log path [format [buffer=size [flush=time]] [if=condition]];

The if parameter (1.7.0) enables conditional logging.
A request will not be logged if the condition evaluates to “0” or an empty string

Combined with map directive its possible to send log events to different logs based on various conditions.

http {

    map $status $normal {
        ~^2  1;
        default 0;
    }
    map $status $abnormal {
        ~^2  0;
        default 1;
    }
    map $remote_addr $islocal {
        ~^127  1;
        default 0;
    }

    server {

        access_log logs/access.log combined if=$normal;
        access_log logs/access_abnormal.log combined if=$abnormal;
        access_log logs/access_local.log combined if=$islocal;

    }  
}

http://nginx.org/en/docs/http/ngx_http_log_module.html
http://nginx.org/en/docs/http/ngx_http_map_module.html

Answer 2

In every question is a part of answer. You were very close:

if ($status != "200") {
    access_log off;
}

Check info for version availability here. http://nginx.org/en/docs/http/ngx_http_core_module.html#variables

Also, almost all access log format vars are available in "modern" versions: http://nginx.org/en/docs/http/ngx_http_log_module.html