Anshul Sharma sharmaansh21

Node - a physical or virtual machine that hosts services
- Nodes also referred to as members.
- Examples
  - Your computer
  - An AWS EC2 instance
  - A bare metal machine in your private data center
Service - executing software that provides utility via an interface
- Typically long-lived process listening on a port(s)
- Examples
A web server (nginx, apache, iis)

What to Expect and Tips

• 45-minute systems interview, focus on responding to real world problems with an unhealthy service, such as a web server or database. The interview will start off at a high level troubleshooting a likely scenario, dig deeper to find the cause and some possible solutions for it. The goal is to probe your knowledge of systems at scale and under load, so keep in mind the challenges of the Facebook environment.
• Focus on things such as tooling, memory management and unix process lifecycle.

Systems

More specifically, linux troubleshooting and debugging. Understanding things like memory, io, cpu, shell, memory etc. would be pretty helpful. Knowing how to actually write a unix shell would also be a good idea. What tools might you use to debug something? On another note, this interview will likely push your boundaries of what you know (and how to implement it).

Design/Architecture

Interview is all about taking an ambiguous question of how you might build a system and letting

PROCESS STATE CODES

Here are the different values that the s, stat and state output specifiers (header "STAT" or "S") will display to describe the state of a process.

CODE	Meaning
D	Uninterruptible sleep (usually IO)
R	Running or runnable (on run queue)
S	Interruptible sleep (waiting for an event to complete)
T	Stopped, either by a job control signal or because it is being traced.
W	paging (not valid since the 2.6.xx kernel)

Moved to git repository: https://github.com/denji/nginx-tuning

NGINX Tuning For Best Performance

For this configuration you can use web server you like, i decided, because i work mostly with it to use nginx.

Generally, properly configured nginx can handle up to 400K to 500K requests per second (clustered), most what i saw is 50K to 80K (non-clustered) requests per second and 30% CPU load, course, this was 2 x Intel Xeon with HyperThreading enabled, but it can work without problem on slower machines.

You must understand that this config is used in testing environment and not in production so you will need to find a way to implement most of those features best possible for your servers.

How does `ls` work?

I wanted to be really able to explain to a fair amount of detail how does the program :command:`ls` actually work right from the moment you type the command name and hit ENTER. What goes on in user space and and in kernel space? This is my attempt and what I have learned so far on Linux (Fedora 19, 3.x kernel).

How does the shell find the location of 'ls' ?

Introduction to Kafka

Kafka acts as a kind of write-ahead log (WAL) that records messages to a persistent store (disk) and allows subscribers to read and apply these changes to their own stores in a system appropriate time-frame.

Terminology:

Producers send messages to brokers
Consumers read messages from brokers
Messages are sent to a topic

	# How to encrypt/decrypt your text/blob secret with AWS KMS with AWS cli

	KEY_ID=alias/my-key
	SECRET_BLOB_PATH=fileb://my-secret-blob
	SECRET_TEXT="my secret text"

	ENCRYPTED_SECRET_AS_BLOB=encrypted_secret_blob
	DECRYPTED_SECRET_AS_BLOB=decrypted_secret_blob # Result of decrypt-blob target

	encrypt-text:

	#!/usr/bin/env python
	# -- coding: utf-8 --
	# Run with
	# sudo consul watch -type=service -service=redis ./consul-iptables.py

	import json
	import subprocess
	import sys

	def main():

	FROM madnight/docker-alpine-wkhtmltopdf as wkhtmltopdf_savior

	# STAGE for bundle & yarn install
	FROM ruby:2.4.3-alpine3.7 as builder

	ENV CA_CERTS_PATH /etc/ssl/certs/
	ENV RAILS_ENV production
	ENV RAILS_LOG_TO_STDOUT true
	ENV RAILS_SERVE_STATIC_FILES true

	What exactly is "iowait"?

	To summarize it in one sentence, 'iowait' is the percentage
	of time the CPU is idle AND there is at least one I/O
	in progress.

	Each CPU can be in one of four states: user, sys, idle, iowait.
	Performance tools such as vmstat, iostat, sar, etc. print
	out these four states as a percentage. The sar tool can
	print out the states on a per CPU basis (-P flag) but most