Alex Shteinikov idooo

Adding 2 nodes to an existing 3-node ZooKeeper ensemble without losing the Quorum

Since many deployments may start out with 3 nodes and so little is known about how to grow a cluster from 3 memebrs to 5 members without losing the existing Quorum, here is an example of how this might be achieved.

In this example, all 5 nodes will be running on the same Vagrant host for the purpose of illustration, running on distinct configurations (ports and data directories) without the actual load of clients.

YMMV. Caveat usufructuarius.

Step 1: Have a healthy 3-node ensemble

This came out of the recent JS Promises debate. @ForbesLindesay was confused by liftA2, so I thought I’d try to explain it.

Let me explain liftA2. I’ll tweak @pufuwozu’s examples so that they return values.

// Promises (called when both succeed)
liftA2(readFIle('hello.txt'), readFile('world.txt'), function(hello, world) {
 return hello + ' ' + world;
});
// Optional values (only inserted into database when both exist)

liftA2(optionalUsername, optionalPassword, function(username, password) {

	def jvmRunFlags = '''
	-Xmx700m
	- ...
	'''.split().toList()

	def jvmTestFlags = '''
	-Dlocally=true
	-ea
	- ...
	'''.split().toList()

	/*
	* An example of how to use a Google Map overlay to display a label on top of marker.
	* This is a slight re-work of http://www.tdmarketing.co.nz/blog/2011/03/09/create-marker-with-custom-labels-in-google-maps-api-v3/
	* I suggest you rather view that blog post, this code is pasted here purely for my own personal reference.
	*/

	var
	point = {
	lat: 37.8478115,
	long: 15.2934327

	//
	// Regular Expression for URL validation
	//
	// Author: Diego Perini
	// Created: 2010/12/05
	// Updated: 2018/09/12
	// License: MIT
	//
	// Copyright (c) 2010-2018 Diego Perini (http://www.iport.it)
	//

	# to generate your dhparam.pem file, run in the terminal
	openssl dhparam -out /etc/nginx/ssl/dhparam.pem 2048

	Edit mc’s ini file (either ~/.mc/ini or ~/.config/mc/ini) and look for the line [Colors]. Then, change the line base_color to this:

	[Colors]
	base_color=linux:normal=white,black:marked=yellow,black:input=,green:menu=black:menusel=white:menuhot=red,:menuhotsel=black,red:dfocus=white,black:dhotnormal=white,black:dhotfocus=white,black:executable=,black:directory=white,black:link=white,black:device=white,black:special=white,black:core=,black:stalelink=red,black:editnormal=white,black