DEV Community: Nyareki Gospel

Zuri Booking Engine Outage - Incident Report and Recovery Analysis

Nyareki Gospel — Tue, 23 Jan 2024 19:11:56 +0000

On the 20th of December 2023, the Zuri Booking Engine experienced a downtime. Here, is the postmortem. We sincerely apologize to all our valued guests who were inconvenienced by this disruption. We empathize with the challenges you faced during this period and assure you that we are committed to implementing measures to prevent such occurrences in the future.

Issue Summary

Commencing at 14:47 hours EAT, 100% of guests attempting to make reservations and complete transactions through the website were redirected to a 500 Internal Server Error page, failing to receive the SDK push required for transaction authorization. Notably, users retained access to other site components, allowing them to view information unrelated to reservations. The root cause of this outage traces back to a recent update implemented a few minutes prior, which inadvertently modified the routing and handling mechanisms for incoming requests. We extend our sincere apologies for any inconvenience caused and are committed to both rectifying the issue promptly and implementing measures to prevent such occurrences in the future. By 16:15 hours, the issue had already been resolved and everything was working alright.

Timeline (East African Time)

14:34 hours - An update pushed to production.
14:47 hours - A customer sent a complaint.
14:47 hours - The engineering team was notified.
15:34 hours - Successful configuration change rollback. The Booking engine was rolled back.
15:35 hours - The engineering team focused on rectifying the update pushed earlier.
16:13 hours - A rectified update was pushed.
16:15 hours - Status page updated to "Resolved".

Root Cause

The underlying cause of the incident stemmed from the deployment of untested code into the production environment. Following the completion of the final component for the booking engine, the responsible engineer conducted testing and introduced some modifications before initiating the code push. Regrettably, the deployed code resulted in the generation of incomplete requests to the backend, triggering an error 500 in the response from the route. While the database underwent updates, the SDK push failed to obtain authorization. Recognizing the issue, an immediate system rollback was executed. Subsequently, the engineering team initiated a rollback of the database and implemented code patches to facilitate the submission of valid requests. Rigorous testing, encompassing various scenarios, was then conducted to ensure the security and efficacy of the revised code. Following successful validation, the corrected code was pushed as the definitive update.

Corrective and Preventative Measures

A comprehensive system analysis conducted the following morning enabled us to formulate the subsequent steps to address potential recurrences of the issue:

Execute a rollback to revert to the originally utilized code.
Address the underlying issue in a systematic, section-by-section manner.
Thoroughly test the patched code for validation.
Progress to deploy the updated website with the implemented patches.
Integrate monitoring mechanisms for requests on the most critical routes to enhance proactive issue detection.

Mastering Python For Web Development

Nyareki Gospel — Sun, 15 May 2022 03:16:42 +0000

Web Development is defined as building and maintaining of websites. When doing this, web developers design, program, publish and maintain databases. The programming exercise is done using html( a mark-up language), css and javascript. Python can be used as well. Python has a couple of frameworks such as Django and Flask that are used to develop websites. In this article, I document the development of an authentication system using Flask, a python framework, in a windows pc. The link to the deployed website is HERE.

Setting Up The Environment.

The first step is to set up a flask environment in which the flask app will be developed. In your desired location, create a folder and name it FlaskAuthSys to stand for Flask Authentication System. Open the Command Prompt. Using cd navigate to the folder FlaskAuthSys. Run the code below:

pip install flask

Use the following code to check the installed packages.

pip freeze

We will also be in need of flask_sqlalchemy, flask_login, flask_wtf and flask_bootstrap. The following lines of code will help you install these requirements. Copy each line separately pasting it on the Command Prompt window then run it.

pip install flask_sqlalchemy
pip install flask_login
pip install flask_wtf
pip install flask_bootstrap

Once this is done, pip freeze will show all the installed features.

Setting Up The Flask Application.

Create a python file myapp.py in the FlaskAuthSys folder. In it, initialise the file by importing all features important to the authentication system with the python code below.

# import flask itself, request, render_template, resirect and url_for
from flask import Flask,request,render_template,redirect,url_for
# import FlaskForm for the authentication details form
from flask_wtf import FlaskForm
# import fields to be used in the form
from wtforms import StringField, PasswordField
# import validation features from wtf
from wtforms.validators import InputRequired, Email, Length
# import python flask bootstrap
from flask_bootstrap import Bootstrap
# import sqlqlchemy for the database we will need later on
from flask_sqlalchemy import SQLAlchemy
# import login features
from flask_login import LoginManager,UserMixin,login_user,login_required,logout_user

import os
import sqlite3
import flask

Let's create our app instance now. Below the above code, type in this:

myapp=Flask(__name__)
if __name__ == '__main__':
    myapp.run(debug=True)

Right below the myapp=Flask(__name__) app instance line, type in the following code block:

@myapp.route('/')
def index():
    return render_template('index.html')
# login section
@myapp.route('/login')
def login():
    return render_template('login.html')
# sign up section
@myapp.route('/signup')
def login():
    return render_template('signup.html')
# the dashboard
@myapp.route('/dashboard')
def login():
    return render_template('dashboard.html')
# log out procedure
@myapp.route('/logout')
def login():
    return redirect(url_for('index'))

Initializing The Database.

The information collected by the user's registration is stored in a database. To begin, install splite3 in your PC referring to this tutorial. Open Command Prompt and navigate to the file FlaskAuth Sys and paste the following code to create a database we will use to store our data.

sqlite3 database.db

to exit sqlite3 type in:

.exit

Back in our myapp.py file, create the fields to be used in data storage and the table Users. Here is how to do this:

class Users(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(20), unique=True)
    email = db.Column(db.String(50), unique=True)
    password = db.Column(db.String(80))

Next we import the table Users to the created database.db. In the Command Prompt open python with:

python

Next, run the following lines in the Command Prompt, one line at a time, to import the table created in myapp.py to the database.db;

from myapp import db
db.create_all()

The table users is now created in the database.

Registration.

When the website user has no account yet, he is not allowed to log in. So that the user logs in the account is first created using the sign up page. Using this code create a sign up page named: signup.html. Store this html file in a folder named templates in the FlaskAuthSys folder.

Back in our myapp.py file, create a registration instance with the code below to specify what way data is to be received for storage:

class RegisterForm(FlaskForm):
    username = StringField('username', validators=[InputRequired(), Length(min=4, max=20)])
    password = PasswordField('password', validators=[InputRequired(), Length(min=8, max=80)])
    email = StringField('email', validators=[InputRequired(), Email(message='Invalid Email'), Length(max=50)])

Next, update the sign up section with the following code:

@myapp.route('/signup', methods=['GET','POST'])
def signup():
    form = RegisterForm()   
    if form.validate_on_submit():
        new_users = Users(username=form.username.data, email=form.email.data, password=form.password.data)
        db.session.add(new_users)
        db.session.commit()

        return '<h1>New user has been created!</h1>'
    return render_template('signup.html', form = form)

The sign up section is completed for now.

Loging In.

This is simple since the table is already created. Create a html file in templates called login.html. Here is my login page.

In the myapp.py python page, create a login instance with this code:

class LoginForm(FlaskForm):
    username = StringField('username', validators=[InputRequired(), Length(min=4, max=20)])
    password = PasswordField('password', validators=[InputRequired(), Length(min=8, max=80)])

Update the login code as follows:

@myapp.route('/login', methods=['GET','POST'])
def login():
    form = LoginForm()
    if form.validate_on_submit():
       users = Users.query.filter_by(username=form.username.data).first()
       if users:
           if users.password == form.password.data:
               login_user(users)
               return redirect(url_for('dashboard'))
       return '<h1> Invalid username or password</h1>'
    return render_template('login.html', form = form)

Up to here, the Registration and login in is Taken care of. The rest of the code for this project is in this GitHub Repository FlakHostedAuthSys. Thank you for reading this article. Find me on twitter @i_njili Leave me a comment in the comment section bellow. Good Day:)

Python 101 : Introduction To Python

Nyareki Gospel — Sun, 24 Apr 2022 09:02:51 +0000

You might be wondering; "why would the inventor of Python name it after a snake?". That bothered me too when I was starting out. Well inventor Guido Van Rossum named his programming language after his favourite British Comedy series, "Monty Python's Flying Circus" and not a snake. He gave it this name because Python is a mysterious, short and unique language. Python is a high-level, general-purpose programming language with dynamic semantics released by Guido Van Rossum in the year 1991 after he had developed it .
Here is why you should learn python today:

Python is easy to read and can be read quite like English because it employs least verbosity. This makes it easy to learn too.
Python has user friendly data structures that add up to its simplicity, increasing it's productivity.
Python comes with an extensive library. It's code can be used for various purposes for example, in regular expressions, databases, emails and even image manipulation.
The extensibility of python is useful in projects. This means it can be written in other languages like C or C++.
Python opens up opportunities for Internet Of Things due to it's heavy featuring in platforms such as Raspberry Pi.

Real World Application Of Python

Python has grown and proven useful since it's birth allowing it's usage in various ways.

Computer Aided Design Applications- These are applications that allow their users create 2D and 3D models digitaly. Python has been employed in the development of these applications for example Blender.
Web Development- With it's wide range of frameworks, Python has been heavily used in the development of websites making the process almost effortless.
Data Science- This field deals with the collection analysis and visualisation of data. Here, Python simplifies the complexity using tools like TensorFlow and Pandas.
Game Development- As games have grown popular, the development of games using python has also grown resulting in it's use in development of games like Battlefield 3 and Pacman.
Software Development- Python's Platform Independence and High Compatibility made it an ideal software development Language.

How Do I Install Python?

Well there is a wide range of ways to do this. The method I find simplest (for Windows Users) is Installing Python from the Microsoft store then in the code editor Visual Studio Code, write you Python program and run it From Visual Studio's Terminal.
Install Visual Studio Code HERE then The Code Runner Extension HERE
You could also check out these tutorials for installation on Linux, Windows or Android.

Getting Started With Python

Now you have the required tools. Let us birth our first program.

On your Desktop create a new folder by the name "PythonFiles".
Start Visual Studio Code and open a new file.
Save the file in the folder PythonFiles as Hello.py

NB

Python files are saved with the suffix '.py'

Type in the following code:

print("Hello World")

Click the run button on the top right corner. The terminal will open displaying:

Hello World

Explanation

The function 'print' in python is used to output the value in it's confines and so in this case the code prints out 'Hello World'

Python Comment.

In programming, a comment is a line of code added to a source code to give an explanation to the code and what it does.
Comments aren't executed with the code. In python, we comment by typing in a hash(#) before the comment as shown bellow.

#comment

The comment above covers a single line only. For multiline comments type in triple quotes(""") before and after the line of code you wish to comment. Here is an example:

"""
This is a
multiline
comment
""""

Python Variables.

Variable in programming are used to store values that are later used by the program to execute tasks. This is how to crate and assign a variable a value:

variable_name = variable_value

There are rules to naming variables. These rules include:

The variables can be named in alphanumeric characters (A-Z),(a-z),(1-9) and (_).
A variable must start with a letter or underscore and not a number.
Variable names are case sensitive.
Variables cannot be named after keywords for example "print".

Here is an example of a variable and its value:

boys = 3

Basic Python Datatypes.

Datatypes are categorisation of data items. There are 3 basic Datatypes in python

- String.

This ranges from a single alphanumeric character to a series of alphanumeric characters. A string can be assigned to a variable in two ways: typing it between double or triple quotation marks as below:

#double quotation marks
people="Ladies and Gentlemen"
print(people)

#Output.
Ladies and Gentlemen

#triple quotation marks
thanks="""Be grateful for everything"""
print(thanks)

#Output.
Be grateful for everything

You can as well output a string without initially declaring it as a variable as we did before:

print('Hello World Again')

#Output.
Hello World Again

- Numeric.

Numeric data is in three forms; Integers, Float and Complex numbers.
- Integersare whole numbers for example 4,96
- Float are numbers with a floating decimal value for example 4.96
- Complex numbers are numbers with complex classes for example cj6+7
Here is how they are assigned:

first = 7 #integer
second = 7.77 #float
third = M40i #complex number

- Boolean.

Boolean integers may have one of the two values true or false.

#boolean
x = false
type(x)
y = true
type(y)

#Output:
<class 'bool'>
<class 'bool'>

The output is verifying the datatype of both y and x is Boolean.

Operators in python.

Arithmetic Operators.

These include addition(+),subtraction(-) ,multiplication(*) ,exponent(**) ,division(/) ,floor division// and modulus(%).
Exponent is used for square roots, floor division divides the numbers then outputs the result rounded off to it's lower digit and modulus returns the remainder during a division. Here is an example of how the arithmetic operators work:

a = 2
b = 9

print(a + b)#addition 
print(b - a)#subtraction
print(b/a)#division
print(b*a)#multiplication
print(b//a)#floor division
print(b**a)#exponent
print(b%a)#modulus

#Output:
11
7
4
18
4
81
1

The addition operation can also concatinate a string:

print("Hello "+"world"+".")

#Output:
Hello world.

Assignment Operators.

These operators assign a variable its value. They include: =, +=, -=, /=, *=, //=,**=, %=.
Here is an illustration of how they are used;

a = 9;
b = 4;
#above the '=' sign assigns the values to the variables

b+=4 #This adds 4 to the value in b then assigns the result to d
print(b)

#Output:
8

All other assignment operators work in ta similar way.

Comparison Operators.

Examples of this are: equal to ==, not equal to !=, greater than >, less than <, greater than or equal to >=and less than or equal to <=. These operators are used to compare variables then return true or false. They are often employed in python conditions for instance if...else conditions.

a = 7
b = 4
print(a==b)#equal to
print(a!=b)#not equal to
print(a<=b)#less than or equal to
print(a>=b)#greater than or equal to
print(a<b)#less than
print(a>b)#greater than

#Output:
False
True
False
True
False
True

Here is some enlightenment: The equal to and not equal to operators can also be used to compare strings as shown below:

print("me"=="you")
print("me"!="you")

#Output:
False
True

Logical Operators.

Logical operators are three in number; and, or and not. When run, they return True or False.
and returns true only when both operands are true and false when both or one of the operands is false. Here is how it works:

print(True and True)
print(True and False)
print(False and True)
print(False and False)

#Output
True
False
False
False

or returns true when one or both operands are true and false when both operands are false.

print(True or True)
print(True or False)
print(False or True)
print(False or False)

#Output
True
True
True
False

not returns the opposite of the operand.

print(not True)
print(not False)

#Output
False
True

Python Logical Conditions

If Statement.

This statement is written using the if keyword. It evaluates whether a condition is true or false then if true goes ahead and executes a specified code.

a = 4
b = 6
if a<b:
   print(6 is greater then 4)

#Output:
6 is greater than 4

If...else Statement.

The If...else statement evaluates a condition and runs one of two codes specified as per the outcome.

a = 4
b = 6
If a>b:
   print("4 is greater than 6")
else:
   print("4 is less than 6")
#note: an if else statement without indentation will result to an error

#Output:
4 is less than 6

If...elif...else Statement.

The elif keyword is adopted in python to allow more than two conditions to be accomodated in a syntax.

a = 10
b = 5
if a=b:
   print(a is equal to b)
elif a>b:
   print(a is greater than b)
else:
   print(a is less than b)

#Output;
a is greater than b

Data Structures In Python.

Data structures provide a way of arranging data so it can be accessed efficiently whenever needed.

Dictionary.

This is an ordered collection of data values that holds the key and value pair that optimizes its functionality. You can create a dictionary with an integer key or a mixed key.
Here is an example of a dictionary:

#with an integer key
one = {
    1:'Be',
    2:'You',
    3:'Everyday'
}
print(one)

#with mixed key
two = {
    Name:'Ace',
    1:[3,4]
}
print(two)

#Output.
{1:'Be', 2:'You', 3:'Everyday'}
{1:[3,4], Name:'Ace',}

Array Datatypes.

Here we will focus on list and tuple.

1. List.

A list in python is an ordered grouping of any arbitrary datatypes that can be accessed by their indexes. Values in a list are assigned indexes starting from zero then one onwards. The first value in a list gets the index 0 then the second 1 and so on. Here is an example of a list:

brands = ['Nike', 'Adidas', 'Puma']
print(brands[1])

#Output:
Adidas

Lists have distinct characteristics from other data structures;

Lists can be nested on other lists.
Lists can be muted in a program.
Lists are accessed by their indexes.
Lists can accommodate any arbitrary values ranging from strings to numeric values.
Lists can be modified:

Accessing values in a list.

shoes=['boots', 'loafers', 'sneakers', 'crocs', 'slides']
print(shoes[3])

#Output:
crocs

Slice of list.

Slice of a list is useful in extraction of subsets in a list. The values are extracted up to a specified index. Here is an example;

shoes=['boots', 'loafers', 'sneakers', 'crocs', 'slides']
print(shoes[0:3])
print(shoes[:3])

#Output:
['boots', 'loafers', 'sneakers']
['boots', 'loafers', 'sneakers']

The list is retrieved up until but not including the value at index 3 in both cases

Updating Items on a list

This is how we update a list's items;

shoes=['boots', 'loafers', 'sneakers', 'crocs', 'slides']
shoes(1)=['monk']
print(shoes[1]

#Output:
['monk']

The 'loafers' in the list has been replaced by the 'monk'.

List Methods.

Methods are specifically designed to modify lists.

Append Method.

Adds an item to a list

shoes=['boots', 'loafers', 'sneakers', 'crocs', 'slides']
shoes.append(chukka)
print(shoes)

#Output:
['boots', 'loafers', 'sneakers', 'crocs', 'slides', 'chukka']

Remove Method.

Removes the first instance of an item in a list

shoes=['boots', 'loafers', 'sneakers', 'crocs', 'slides']
shoes.remove(boots)
print(shoes)

#Output:
['loafers', 'sneakers', 'crocs', 'slides',]

2. Tuple.

Tuple is quite similar to list apart from a few features as listed below.

Tuples are defined by enclosing items in them in parenthesis () and not square brackets []
Tuples are immutable

school = ('medicine'', 'law', 'engineering', 'education', 'business')
print(school)

#Output
['medicine'', 'law', 'engineering', 'education', 'business']

The greatest resource in life being time, let me thank you for spending yours on this publication. Gratitude.
Find me on Twitter at i_njili