openrusty nginx lua http traffic replication with multiple capture example

nginx.conf

worker_processes 2;

events {
  worker_connections 1024;
}

http {
  access_log /dev/stderr combined;

  keepalive_timeout 65;
  resolver 8.8.8.8;

  lua_package_path "$prefix/lualib/?.lua;;";

  lua_shared_dict locks 1M;
  lua_shared_dict cache 10M;

  upstream slave1 {
    server server1.com fail_timeout=10;
    keepalive 32;
  }

  upstream slave2 {
    server server2.com fail_timeout=10;
    keepalive 32;
  }

  # see https://github.com/openresty/lua-resty-core
  init_by_lua '
    require "resty.core"
  ';

  server {
    listen 8080;

    proxy_set_header            X-Real-IP       $remote_addr;
    proxy_set_header            X-Forwared-For  $proxy_add_x_forwarded_for;

    location /gateway_slave1 {
        internal;
        rewrite /gateway_slave1(.*) $1 break;

        proxy_pass                 http://slave1;
        client_max_body_size       10m;
        client_body_buffer_size    1m;
        proxy_buffer_size          32k;
        proxy_buffers              10 128k;
        proxy_busy_buffers_size    128k;
        proxy_temp_file_write_size 10m;
    }

    location /gateway_slave2 {
        internal;
        rewrite /gateway_slave2(.*) $1 break;

        proxy_pass                 http://slave2;
        client_max_body_size       10m;
        client_body_buffer_size    1m;
        proxy_buffer_size          32k;
        proxy_buffers              10 128k;
        proxy_busy_buffers_size    128k;
        proxy_temp_file_write_size 10m;
    }

    location ~* ^/(A|B)/Insert {
        default_type text/plain;

        content_by_lua '
            ngx.req.read_body()

            local upstream = require "ngx.upstream"
            local body = ngx.req.get_body_data()

            local reqs = {}
            for _, u in ipairs(upstream.get_upstreams()) do
                if string.sub(u,1,5) == "slave" then
                    table.insert(reqs, { "/gateway_"..u..ngx.var.uri, { method = ngx.HTTP_POST, args = ngx.var.args, always_forward_body = true } })
                end
            end

            if #reqs == 0 then
                ngx.log(ngx.ERR, "No /Insert upstreams found on request ", ngx.var.request_uri)
                ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
                return
            end

            local bad = 0
            local good = 0
            local resps = { ngx.location.capture_multi(reqs) }
            for i, r in ipairs(resps) do
                if r.status ~= 200 then
                    ngx.log(ngx.ERR, "Upstream ", reqs[i][1], " failed to make a POST to ", ngx.var.uri, ", status = ", r.status, ", resp = ", r.body)
                    bad = bad + 1
                else
                    good = good + 1
                end 
            end

            if good > 0 then
                ngx.say("OK")
                ngx.exit(ngx.HTTP_OK)
            else
                ngx.say("All upstreams failed")
                ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
            end
        ';
    }
  }
}