Customize the Default Log Format in Kong API Gateway

Role of Nginx

Kong is built on NGINX, and uses Lua to implement its API functionality, whereas the API management module relies completely on native, high‑performance capabilities that are implemented as NGINX Plus modules. So the format of the log lines in Kong is determined by corresponding configuration in the NGINX service.

# Sample Log Line from Default log Pattern - - [05/May/2021:08:19:40 +0000] "POST /api/service/getinfo HTTP/1.1" 200 2313 "-" "curl/7.61.1"

# Parameters in the above log line
$remote_addr - $remote_user [$time_local] "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent"

Injecting Nginx directives

Tweaking the Nginx configuration of your Kong instances allows you to update the default configurations. When Kong starts, it builds an Nginx configuration file. You can inject custom Nginx directives to this file directly via your Kong configuration.

nginx_http_log_format=show_everything '\$time_iso8601 - \$bytes_sent - \$request - \$status - \$remote_addr'
proxy_access_log=/dev/stdout show_everything

Environment variables

This is my favorite method and one of the reasons which make Kong super easy to use. When loading properties out of a configuration file, Kong will also look for environment variables of the same name. This allows you to fully configure Kong via environment variables, which is very convenient for container-based infrastructures, for example:

-e "KONG_NGINX_HTTP_LOG_FORMAT=show_everything '\$time_iso8601 - \$bytes_sent - \$request - \$status - \$remote_addr'"
-e "KONG_PROXY_ACCESS_LOG=/dev/stdout show_everything"

My Log Format

For my case, I wanted a very simple log format with minimal information required to do any troubleshooting. So what I wanted to see for the successful API requests were,

  • Request source IP
  • Request time
  • Response time
  • API Request information (HTTP method, Context path etc )
  • API Response code
  • User Agent Header (to identify the requestor)
$remote_addr - $remote_user [$time_local] $start_time "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent"
# To get the request time, add the below env variable
KONG_NGINX_PROXY_SET_BY_LUA=$$start_time 'return'
# To get the request time, add the below env variable
KONG_NGINX_PROXY_SET_BY_LUA=$$start_time 'return'
# Below env variables are to define your log pattern:
KONG_PROXY_ACCESS_LOG=/dev/stdout show_everything
KONG_NGINX_HTTP_LOG_FORMAT=show_everything '$remote_addr - $remote_user [$time_local] $start_time - "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent"' - - [05/May/2021:08:59:49 +0000] 1620205189.259 - "POST /api/service/getinfo HTTP/1.1" 200 2313 "-" "curl/7.61.1"# Format of the log line:
# {Source IP} - {Remote User} [{Response time}] {Request time} .....
KONG_NGINX_PROXY_SET_BY_LUA=$$start_time 'return'
KONG_PROXY_ACCESS_LOG=/dev/stdout show_everything
KONG_NGINX_HTTP_LOG_FORMAT=show_everything '$remote_addr - $remote_user [$time_local - $msec] $start_time - $request_time "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent"'

# Resulting Log Format:
# {Source IP} - {Remote User} [{Response time} - {Response time in milliseconds}] {Request time} - {Duration of the request} ..... - - [05/May/2021:08:59:49 +0000 - 1620205189.300] 1620205189.259 - 0.041 "POST /api/service/getinfo HTTP/1.1" 200 2313 "-" "curl/7.61.1"
  • Wednesday, May 5, 2021 8:59:49.300 AM
  • Wednesday, May 5, 2021 4:59:49.300 PM GMT+08:00
  • Wednesday, May 5, 2021 8:59:49.259 AM
  • Wednesday, May 5, 2021 4:59:49.259 PM GMT+08:00



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Danuka Praneeth

Danuka Praneeth

Senior Software Engineer | BSc (Hons) Engineering | CIMA | Autodidact | Knowledge-Seeker