Full NGINX Logging Example

In a previous post I talked about how to setup NGINX to log both the request and response headers and bodies to help with debugging. It’s a lot easier to set up a HTTP reverse proxy than sort out all the private keys when trying to capture HTTPS with wireshark.

I needed to use that again recently and it took me a little while to remember exactly how to put it all together again, so this is just a really short follow up post with a full minimal example of the nginx.conf file needed.

worker_processes 1;
load_module modules/ndk_http_module.so;
load_module modules/ngx_http_lua_module.so;
pcre_jit on;

events {
  worker_connections 1024;

error_log /dev/stderr;

http {
  log_format log_req_resp '$remote_addr - $remote_user [$time_local] '
  '"$request" $status $body_bytes_sent '
  '"$http_referer" "$http_user_agent" $request_time req_body:"$request_body" resp_body:"$resp_body" '
  'req_headers:"$req_header" resp_headers:"$resp_header"';

  server {
    listen 80;
    access_log /dev/stdout log_req_resp;

    root /var/www/html;

    lua_need_request_body on;

    set $resp_body "";
    body_filter_by_lua '
      local resp_body = string.sub(ngx.arg[1], 1, 1000)
      ngx.ctx.buffered = (ngx.ctx.buffered or "") .. resp_body
      if ngx.arg[2] then
        ngx.var.resp_body = ngx.ctx.buffered

    set $req_header "";
    set $resp_header "";
    header_filter_by_lua '
      local h = ngx.req.get_headers()
      for k, v in pairs(h) do
        if (type(v) == "table") then
          ngx.var.req_header = ngx.var.req_header .. k.."="..table.concat(v,",").." "
          ngx.var.req_header = ngx.var.req_header .. k.."="..v.." "
      local rh = ngx.resp.get_headers()
      for k, v in pairs(rh) do
        ngx.var.resp_header = ngx.var.resp_header .. k.."="..v.." "


It also has a small improvement to allow for duplicate HTTP headers in the request (which is in spec). It will now concatenate the values in to a comma separated list.

This is intended to be used with the following Docker container (the default nginx container doe not have the lua module installed)

FROM debian:latest

RUN apt-get update && apt-get install -y libnginx-mod-http-lua libnginx-mod-http-ndk

CMD ["nginx", "-g", "daemon off;"]

Run as follows

docker run --rm -v `pwd`/nginx.conf:/etc/nginx/nginx.conf:ro -p 80:80 custom-nginx

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