Scott Francis csfrancis

Debugging DNS

This is a story about how I debug things. We're big users of NGINX and Lua at Shopify. Lately, we've been looking at implementing support to add and remove upstream peers to lua-upstream-nginx-module. Step 1 is to get the tests working for the module to make sure the world's in a sane state. I built a development build of NGINX and ran the tests, and this is when the trouble started.

A few of the tests were failing with similar errors:

#   Failed test 'TEST 4: sample in README - response_body - response is expected (req 0)'
#   at /usr/local/share/perl/5.18.2/Test/Nginx/Socket.pm line 1277.
# @@ -1,5 +1,5 @@
#  upstream foo.com:

	#!/usr/bin/env ruby

	NGINX_PID_FILE = "/var/run/nginx.pid"
	NGINX_OLD_PID_FILE = "/var/run/nginx.pid.oldbin"
	NGINX_CONF_FILE = "/etc/nginx/nginx.conf"
	NGINX_BIN = "/usr/sbin/nginx"
	LD_OVERRIDES = "/etc/nginx/ld-overrides"
	DEFAULT_NGINX_WORKERS = 2

	def with_term_color(color, eol: true)

	6040 12:07:29.991944 select(16, [14 15], NULL, NULL, {43, 387221} <unfinished ...>
	6040 12:07:30.149445 <... select resumed> ) = 1 (in [14], left {43, 229785})
	6040 12:07:30.149520 fcntl(14, F_GETFL <unfinished ...>
	6040 12:07:30.149534 <... fcntl resumed> ) = 0x802 (flags O_RDWR\|O_NONBLOCK)
	6040 12:07:30.149551 accept4(14, <unfinished ...>
	6040 12:07:30.149566 <... accept4 resumed> {sa_family=AF_INET, sin_port=htons(37964), sin_addr=inet_addr("127.0.0.1")}, [16], SOCK_CLOEXEC) = 26
	6040 12:07:30.149630 recvfrom(26, <unfinished ...>
	6040 12:07:30.149647 <... recvfrom resumed> "GET /services/ping HTTP/1.0\r\nX-R"..., 16384, MSG_DONTWAIT, NULL, NULL) = 131
	6040 12:07:30.150084 write(26, "HTTP", 4 <unfinished ...>
	6040 12:07:30.150128 <... write resumed> ) = 4

	From 25ec18a4c341955e4e6bd051a06b9d92d09e2d33 Mon Sep 17 00:00:00 2001
	From: Justin Li <[email protected]>
	Date: Thu, 4 Feb 2016 23:15:42 +0000
	Subject: [PATCH] feature: Add upstream.current_upstream_name() to return the
	current proxy target

	---
	README.md \| 27 ++++++++++++
	src/ngx_http_lua_upstream_module.c \| 44 ++++++++++++++++++++
	t/sanity.t \| 84 ++++++++++++++++++++++++++++++++++++++

	unbind C-b
	set -g prefix C-a
	bind a send-prefix

	unbind ^C
	bind ^C new-window
	bind c new-window

	unbind ^a
	bind C-a last-window

	-- A timer that uses the rdtsc instruction to read the CPU timestamp counter.
	--
	-- Requires DynAsm with Lua mode: https://github.com/luapower/dynasm
	--
	-- Use it like this:
	--
	-- local tsc_timer = require('tsc_timer')
	-- local t = tsc_timer.start()
	-- ... do some things ...
	-- t:stop()

	# Updated for Ruby 2.3
	string_t = None

	def get_rstring(addr):
	s = addr.cast(string_t.pointer())
	if s['basic']['flags'] & (1 << 13):
	return s['as']['heap']['ptr'].string()
	else:
	return s['as']['ary'].string()

	c = 0
	v = head = gdb.parse_and_eval('it')
	while v.dereference() != None and c < 100:
	if c > 0 and v == head:
	break
	c += 1
	v = v.dereference()['h_next']

	print c

	#!/bin/bash
	#
	# Show if stats by sampling /sys/.
	# Originally stolen from http://unix.stackexchange.com/questions/41346/upload-download-speed-in-tmux-status-line

	run_segment() {
	sleeptime="0.5"
	iface="eth0"
	RXB=$(</sys/class/net/"$iface"/statistics/rx_bytes)
	TXB=$(</sys/class/net/"$iface"/statistics/tx_bytes)