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Virtual Hosts on nginx (CSC309)

When hosting our web applications, we often have one public IP address (i.e., an IP address visible to the outside world) using which we want to host multiple web apps. For example, one may wants to host three different web apps respectively for example1.com, example2.com, and example1.com/images on the same machine using a single IP address.

How can we do that? Well, the good news is Internet browsers

Riemann is a quite simple but powerful monitoring system. In its core it is an event processing framework allowing a user to handle an incoming event stream. Events are small objects that originate from a host, that has a service and metric value associated with it. Events may also have tags and a free text description. This simple data structure enables an application transmit both exception tracebacks and application metric data using the same mechanism.

Riemann has a few problems though. First, it is a single-machine application, only allowing vertical scaling. Secondly, there's no redundancy or availability solution. In this post we'll try to address the first issue.

	#!/bin/sh

	sudo yum -y install js-devel

	mkdir -p ~/bin
	curl -L http://github.com/micha/jsawk/raw/master/jsawk > ~/bin/jsawk
	chmod 755 ~/bin/jsawk

	#!/usr/bin/env ruby

	# estimate the dewpoint temperature
	def dew_point(temp, rv)
	e = 6.1121 * (10 ** (7.502 * temp / (237.7 + temp)))
	p = (rv * e) / 100.0
	dp = (-430.22 + 237.7 * Math.log(p))/(-(Math.log(p)) + 19.08);
	end

	# estimate the wet bulb temperature

	# Linux. Act upon an event in a log file
	# www.fduran.com

	apt-get upgrade; apt-get install inotify-tools

	# create file myalert.sh:
	# example finding Exception in tomcat log and sending email

	#!/bin/bash
	while inotifywait -e modify /path/to/file.log; do

	vagrant@precise64:~$ irb
	1.9.3-p484 :002 > require "riemann"
	=> true
	# Activate maintenance-mode:
	1.9.3-p484 :010 > Riemann::Client.new << {service: "maintenance-mode", host: "precise64", state: "active", ttl: Float::INFINITY}
	=> nil
	# Deactivate maintenance-mode:
	1.9.3-p484 :011 > Riemann::Client.new << {service: "maintenance-mode", host: "precise64", state: nil, ttl: Float::INFINITY}
	=> nil

	from __future__ import print_function

	from snimpy.manager import Manager as M
	from snimpy.manager import load
	from snimpy.snmp import SNMPNoSuchInstance

	#import pymysql


	# Load up SNMP MIBs

	<% header "Content-Type" => "text/html" %>
	<h1>Let's run some ruby code: <%= rand %></h1>

	# Idempotent way to build a /etc/hosts file with Ansible using your Ansible hosts inventory for a source.
	# Will include all hosts the playbook is run on.
	# Inspired from http://xmeblog.blogspot.com/2013/06/ansible-dynamicaly-update-etchosts.html

	- name: "Build hosts file"
	lineinfile: dest=/etc/hosts regexp='.*{{ item }}$' line="{{ hostvars[item].ansible_default_ipv4.address }} {{item}}" state=present
	when: hostvars[item].ansible_default_ipv4.address is defined
	with_items: groups['all']