bangadennis

System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

1. Clarify and agree on the scope of the system

• User cases (description of sequences of events that, taken together, lead to a system doing something useful)
  • Who is going to use it?
  • How are they going to use it?

bangadennis

echo "Install the app into DHIS app"
cd dist/myapp
curl -X POST -u user:password -F file=@myapp.zip https://mydhis2url/api/apps
echo "app installed into DHIS"

bangadennis

SSH Slackbot

This is a simple slackbot to post successful SSH logins to a slack channel to help you keep track of server access.

Step 1

Create an incoming webhook for your slack community.

Step 2

Create /etc/ssh/sshslack.sh

bangadennis

Paste your code as one comment split.

• Your full name and Reg Number
• Backwardpropagation
• KNN
• SOM

bangadennis

--PostgreSQL Query: [ Get all running queries ]--

SELECT pid, datname, usename, client_addr, now() - query_start as "runtime", query_start, waiting, state, query
FROM pg_stat_activity
ORDER BY runtime DESC;

--PostgreSQL Query: [ Get all running queries – More than X minutes/hours/days ]--

SELECT pid, datname, usename, client_addr, now() - query_start as "runtime", query_start, waiting, state, query
FROM pg_stat_activity

bangadennis

% Lowpass digital filter with Chebyshev-I analog prototype
%

function lowpass
% Digital Filter Specifications:
wp = 0.125*2*pi; % digital passband frequency in Hz (normalized)
ws = 0.1375*2*pi; % digital stopband frequency in Hz (normalized)
Rp = 0.5; % passband ripple in dB
As = 20; % stopband attenuation in dB
% Analog Prototype Specifications:

bangadennis

// takes the form field value and returns true on valid number
function valid_credit_card(value) {
  // accept only digits, dashes or spaces
	if (/[^0-9-\s]+/.test(value)) return false;

	// The Luhn Algorithm. It's so pretty.
	var nCheck = 0, nDigit = 0, bEven = false;
	value = value.replace(/\D/g, "");

	for (var n = value.length - 1; n >= 0; n--) {

bangadennis

/**
 * Luhn algorithm in JavaScript: validate credit card number supplied as string of numbers
 * @author ShirtlessKirk. Copyright (c) 2012.
 * @license WTFPL (http://www.wtfpl.net/txt/copying)
 */
var luhnChk = (function (arr) {
    return function (ccNum) {
        var 
            len = ccNum.length,
            bit = 1,

bangadennis

#!/bin/bash

# for use with cron, eg:
# 0 3 * * * postgres /var/db/db_backup.sh foo_db

if [[ -z "$1" ]]; then
    echo "Usage: $0 <db_name> [pg_dump args]"
    exit 1
fi

bangadennis

# terminal colors, Git branch in prompt, where am i
export CLICOLOR=1
export TERM=xterm-color
export LSCOLORS=ExFxCxDxBxegedabagacad

parse_git_branch() {
  git branch --no-color 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/\ →\ \1/'
}
export PS1='\[\e[1;37m\][\[\e[1;35m\]\u\[\e[1;37m\]:\[\e[1;36m\]\w\[\e[1;33m\]$(parse_git_branch)\[\e[1;37m\]]$ \[\e[0m\]'