Sai Kothapalle seeker815

Overview

Some notes about:

Explaining why current day Linux memory swap thrashing still happens (as of 2016).
Mitigating "stop the world" type thrashing issues on a Linux workstation when it's under high memory pressure and where responsiveness is more important than process completion.
Prioritizing and limiting memory use.
Older ulimit versus newer CGroup options.

These notes assume some basic background knowledge about memory management, ulimits and cgroups.

`vs` Questions

http://stackoverflow.com/questions/804115 (rebase vs merge).
https://www.atlassian.com/git/tutorials/merging-vs-rebasing (rebase vs merge)
https://www.atlassian.com/git/tutorials/undoing-changes/ (reset vs checkout vs revert)
http://stackoverflow.com/questions/2221658 (HEAD^ vs HEAD~) (See git rev-parse)
http://stackoverflow.com/questions/292357 (pull vs fetch)
http://stackoverflow.com/questions/39651 (stash vs branch)
http://stackoverflow.com/questions/8358035 (reset vs checkout vs revert)

Kafka Cheatsheet

Kafka Operations

Run the commands on any of the kafka brokers (APIs in v0.10)

List all Kafka Topics

Installing Prometheus on Ubuntu 16.04

This gist is a compilation of two tutorials. You can find the original tutorials here and here. What should you know before using this? Everything can be executed from the home folder. For easier cleanup at the end you can make directory where you'll download everything, and then just use rm -rf .. Although, you should be careful. If some strange bugs arise unexpectedly somewhere sometimes, just keep in mind that some user names have underscores in them (this is probably nothing to worry about).

Create Users

sudo adduser --no-create-home --disabled-login --shell /bin/false --gecos "Prometheus Monitoring User" prometheus
sudo adduser --no-create-home --disabled-login --shell /bin/false --gecos "Node Exporter User" node_exporter
sudo adduser --no-create-home --disabled-login --shell /bin/false --gecos "Alertm

Recently, Let's Encrypt launched free wildcard certificates. While this is good news in and of itself, as it removes one of the last remaining reasons for expensive commercial certificates, I've unfortunately seen a lot of people dangerously misunderstand what wildcard certificates are for.

Therefore, in this brief post I'll explain why you probably shouldn't use a wildcard certificate, as it will put your security at risk.

A brief explainer

It's generally pretty poorly understood (and documented!) how TLS ("SSL") works, so let's go through a brief explanation of the parts that are important here.

The general (simplified) idea behind how real-world TLS deployments work, is that you:

	# AWS Version 4 signing example
	#
	# Example:
	# Authorization: AWS4-HMAC-SHA256 Credential=AKIDEXAMPLE/20150830/us-east-1/iam/aws4_request, SignedHeaders=content-type;host;x-amz-date, Signature=5d672d79c15b13162d9279b0855cfba6789a8edb4c82c400e06b5924a6f2b5d7

	# Formulae:
	# CanonicalRequest =
	# HTTPRequestMethod + '\n' +
	# CanonicalURI + '\n' +
	# CanonicalQueryString + '\n' +

	Put this in your `local-configure.yml` file, add as many users as you need:

	users:
	- name: fulvio
	sudoer: yes
	auth_key: ssh-rsa blahblahblahsomekey this is actually the public key in cleartext
	- name: plone_buildout
	group: plone_group
	sudoer: no
	auth_key: ssh-rsa blahblahblah ansible-generated on default

	$ docker-compose up -d # start containers in background
	$ docker-compose kill # stop containers
	$ docker-compose up -d --build # force rebuild of Dockerfiles
	$ docker-compose rm # remove stopped containers
	$ docker ps # see list of running containers
	$ docker exec -ti [NAME] bash # ssh to the container

	# list all images
	docker images

	---
	- name: Create Instance in AWS
	hosts: localhost
	connection: local
	gather_facts: false

	vars:
	aws_access_key: "xxxxxx"
	aws_secret_key: "xxxxxx"
	security_token: "xxxxxx"

	$ s3cmd get s3://us-east-1.elasticmapreduce/libs/s3distcp/1.latest/s3distcp.jar
	$ hadoop jar ./s3distcp.jar --src s3a://<bucket>/input/ --dest=s3a://<bucket>/output