How to change log format in nginx?

Question

Nginx

I change the log format as follows

server{
...
  log_format piwik '{"ip": "$remote_addr",'
                '"host": "$host",'
                '"path": "$request_uri",'
                '"status": "$status",'
                '"referrer": "$http_referer",'
                '"user_agent": "$http_user_agent",'
                '"length": $bytes_sent,'
                '"generation_time_milli": $request_time,'
                '"date": "$time_iso8601"}';

    access_log  /path/to/log/log_access.log piwik;
    error_log   /path/to/log/log_error.log piwik;
...
}

But upon reboot, nginx swears at the wrong config.

Answer 1

The error_log cannot be formatted.
log_format should be inside http, not server.

Answer 2

Move log_format to http context