Quickly ssh into repeatly new Linux instances with same IP without host key check

WARNING: this is extremely dangerous on networks not completely TRUSTED

Host 10.10.* *.mycompany.org
  User myuser
  IdentityFile /home/myuser/.ssh/my_ssh_key
  StrictHostKeyChecking no
  UserKnownHostsFile=/dev/null

Total n00b’s guide to Big O, Big Ω, & Big θ

Crazy brillant!

https://medium.com/@.RT/total-n00bs-guide-to-big-o-big-%CF%89-big-%CE%B8-aa259ae8a1c2

Total n00b’s guide to Big O, Big Ω, & Big θ

tcpdump -nnXSs

Taken: https://www.askbjoernhansen.com/2007/07/12/how_to_dump_packets_with_tcpdump.html

I always forget the parameters for this and have to look them up in the man page, so enough of that:

 tcpdump -nnXSs 0 port 80

• "-nn" makes it not lookup hostnames in DNS and service names (in /etc/services) for respectively faster and cleaner output. 
• "-X" makes it print each packet in hex and ascii; that's really the useful bit for tracking headers and such 
• "-S" print absolute rather than relative TCP sequence numbers - If I remember right this is so you can compare tcpdump outputs from multiple users doing this at once 
• "-s 0" by default tcpdump will only capture the beginning of each packet, using 0 here will make it capture the full packets. We are debugging, right? 

<description>[\w\s\n&\.\-,;]*</description>

perl cli regex

perl -pe 's/^(.+)\/([^\s]+)\-([v0-9.]+)\-*([Final|GA|M2|rc|beta|R5]*).jar$/$2\t$3\t$4/'

key git book pages to read

• https://git-scm.com/book/en/v2/Git-Branching-Basic-Branching-and-Merging
• https://git-scm.com/book/en/v2/Git-Branching-Branching-Workflows

packer: virtualbox

Prep

• Vagrant
• vagrant init hashicorp/precise64
• vagrant up
• vagrant destroy -f

Generate

• Packer
• find ~/.vagrant.d/ -name '*ovf' -ls | grep hashi
• create ex001.json
• see below
• fix "source_path" to ovf file to match your system
• packer validate ex001.json
• packer build ex001.json
• vagrant box add my-box-001 packer_virtualbox-ovf_virtualbox.box --force

Test

• mkdir test001
• cd test001
• vagrant init
• in generated "Vagrantfile", change 1st line to 2nd line
•   config.vm.box = "base"
•   config.vm.box = "my-box-001"
• vagrant up
• vagrant ssh
• cat /var/tmp/welcome.txt
• should say, "welcome001"
• vagrant destroy -f

Cleanup

• vagrant box remove my-box-001 --force
• vagrant box remove hashicorp/precise64 --force

---

ex001.json

{
  "builders": [{
      "type": "virtualbox-ovf",
      "source_path": "<path to your home dir>/.vagrant.d//boxes/hashicorp-VAGRANTSLASH-precise64/1.1.0/virtualbox/box.ovf",
      "ssh_username": "vagrant",
      "ssh_password": "vagrant",
      "shutdown_command": "echo 'packer' | sudo -S shutdown -P now"
    }],
    "provisioners": [
        {
            "type": "shell",
            "inline":[ "echo welcome001 > /var/tmp/welcome.txt" ]
        }
    ],
    "post-processors": ["vagrant"]
}

end is nigh: serverless

"For a small company focused on rapid growth, the last thing we wanted to deal with was disk space and memory management, logging agents, security patches, operating system updates, and other traditional server management processes."

recursive

def recursive_countdown(x):
    print('Countdown: ' + str(x))
    if x == 1:
        return 1
    else:
        return recursive_countdown(x - 1)

recursive_countdown(5)


def recursive_fib(x):
    #print('Fib: ' + str(x))
    if x in [0, 1]:
        return x
    else:
        return (recursive_fib(x - 1) + recursive_fib(x -2 ))

# this algo can be easily improved if answers are indexed

print(recursive_fib(5))
print(recursive_fib(6))
print(recursive_fib(7))
print(recursive_fib(8))

Python: sort by value then key

No idea yet how this works, or why.

>>> d = {'apple': 7, 'banana': 3, 'almond': 7, 'peach': 4, 'beetroot': 3}
>>> sorted(d.iteritems(), key=lambda(k, v): (-v, k))
[('almond', 7), ('apple', 7), ('peach', 4), ('banana', 3), ('beetroot', 3)]

Basic Ansible in 10 mins

• "site.yml" file
• playbook containing
• "roles" that will be applied to individual host groups / "hosts"
• how the hosts will be accessed
• and by what user to run as
• Puppet equivalent is "nodes.pp"
• "hosts" file
• use real/local DNS hostname to define which hosts are in which hostgroups
• example: webserver1, webserver2, haproxy1, haproxy2, mongo1, mongo2
• some variables like "port" can be added too
• "group-vars" directory
• key/value pairs to use when generating output from template files
• files named identically to hostgroup names defined in "hosts" file
• these are more in-line in Puppet, and less controllable/flexible
• "roles" directory
• Puppet equivalents are "modules"/"classes"
• directories arbitrarily named to match "roles" in site.yml
• e.g. "tomcat", "common", "mongod"
• "templates" directory
• files with variables that are resolved using "group-vars" key/values
• moved on to target systems using task keyword "template"
• same name is used in Puppet
• "files"
• raw files to be moved into place on the target filesystems
• used by tasks with keyword "file"
• same name used in Puppet
• "handlers"
• "main.yml"
• control system services on target systems
• "service" keyword
• "state", e.g. "restarted"
• in Puppet, these are not broken out from other "resources"
• "tasks"
• this is the core list of actions to perform on target systems
• Puppet equivalents are "includes"/"classes", maybe "modules" as well
• "main.yml"
• collection of tasks
• uses yml structure
• "name" is arbitrary reference for developers
• ansible keyword to perform some action on the system
• ansible keywords: "file", "template", "command"
• puppet equivalents are called "resources"
• conditionals/dependencies: "when", "notify", "wait_for"

Keeping up with Hashicorp's Vault

To retrieve secrets, employees replace plaintext secrets with a call to Secrets Manager APIs, eliminating the need to hard-code secrets in source code or update configuration files and redeploy code when secrets are rotated.