Hanynowsky hanynowsky

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.

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

	# Sends events to Flapjack for notification routing. See http://flapjack.io/
	#
	# This extension requires Flapjack >= 0.8.7 and Sensu >= 0.13.1
	#
	# In order for Flapjack to keep its entities up to date, it is necssary to set
	# metric to "true" for each check that is using the flapjack handler extension.
	#
	# Here is an example of what the Sensu configuration for flapjack should
	# look like, assuming your Flapjack's redis service is running on the
	# same machine as the Sensu server:

	# 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']

	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

	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

	# 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

	#!/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

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