nginx.conf

http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    log_format  ltsv  'domain:$host\t'
                      'host:$remote_addr\t'
                      'user:$remote_user\t'
                      'time:$time_local\t'
                      'method:$request_method\t'
                      'path:$request_uri\t'
                      'protocol:$server_protocol\t'
                      'status:$status\t'
                      'size:$body_bytes_sent\t'
                      'referer:$http_referer\t'
                      'agent:$http_user_agent\t'
                      'response_time:$request_time\t'
                      'cookie:$http_cookie\t'
                      'set_cookie:$sent_http_set_cookie\t'
                      'upstream_addr:$upstream_addr\t'
                      'upstream_cache_status:$upstream_cache_status\t'
                      'upstream_response_time:$upstream_response_time';

    access_log  /var/log/nginx/access.log  ltsv;

    ...snip...

    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-For $http_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;

    include /etc/nginx/conf.d/*.conf;
}

td-agent.conf

<source>
  type tail
  path /var/log/nginx/access.log
  format ltsv
  time_format %d/%b/%Y:%H:%M:%S %z
  tag td.nginx.access
  pos_file /var/log/td-agent/nginx_access.pos
</source>

<source>
  type tail
  path /var/log/nginx/error.log
  format /^(?<time>.+) \[(?<level>[^\]]+)\] *(?<message>.*)$/
  time_format %Y/%m/%d %H:%M:%S
  tag td.nginx.error
  pos_file /var/log/td-agent/nginx_error.pos
</source>