conditionally logging $request_body based on location in nginx config - nginx

Question

I need to configure Nginx to log the $request_body only for certain location blocks.
Inspired by this post, I expected the following to work:
http {
log_format l2met "request_body = $xxxx";
access_log logs/nginx/access.log l2met;
error_log logs/nginx/error.log;
server {
location /path/to/log {
set $xxxx $request_body;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://app_server;
}
location / {
set $xxxx "NOT_LOGGED";
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://app_server;
}
}
}
However, the request body just gets printed as -
I can print the $request_body all the time with this:
http {
log_format l2met "request_body = $request_body";
access_log logs/nginx/access.log l2met;
error_log logs/nginx/error.log;
server {
location /path/to/log {
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://app_server;
}
location / {
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://app_server;
}
}
}
I can conditionally set the logging with this:
http {
log_format l2met "xxxx = $xxxx";
access_log logs/nginx/access.log l2met;
error_log logs/nginx/error.log;
server {
location /path/to/log {
set $xxxx "NEED TO LOG REQUEST BODY HERE";
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://app_server;
}
location / {
set $xxxx "NOT_LOGGED";
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://app_server;
}
}
}
For some reason, it seems that as soon as I reference $request_body from inside a location block, the log output changes to -.
I've tried adding client_body_in_single_buffer to the http block, but that doesn't seem to help.
How do I make this work?
I'm using the version of nginx that was installed by default with apt-get:
$ nginx -v
nginx version: nginx/1.1.19

Answer 1

You could declare any number of log_formats and use ones that you need.
http {
log_format l2met 'measure#nginx.service=$request_time request_id=$http_x_request_id';
log_format capturebody "request_body = $request_body";
access_log logs/nginx/access.log l2met;
server {
...
location / {
...
}
location /other/ {
# this is the location where you need to log $request_body
access_log logs/nginx/access.log capturebody;
...
}
...
}
}