Jürgen Keck j-keck

Getting a shell on each node

I run several K8S cluster on EKS and by default do not setup inbound SSH to the nodes. Sometimes I need to get into each node to check things or run a one-off tool.

Rather than update my terraform, rebuild the launch templates and redeploy brand new nodes, I decided to use kubernetes to access each node directly.

Alternative option

https://github.com/alexei-led/nsenter

Problem

The MPOW Bluetooth 5 dongle (Model: BH456A) does not work out of the box on Ubuntu 20.04 (kernel 5.4.0-42).

Solution

Patch the bluetooth kernel module and copy the firmware binaries to /lib/firmware.

Copy the fimware

Optics By Example Cheat Sheets

The following are appendices from Optics By Example, a comprehensive guide to optics from beginner to advanced! If you like the content below, there's plenty more where that came from; pick up the book!

Operators
Composition Guide
Substitution Guide
Optical Constarints and Types

Operator Cheat Sheet

Quick Tips for Fast Code on the JVM

I was talking to a coworker recently about general techniques that almost always form the core of any effort to write very fast, down-to-the-metal hot path code on the JVM, and they pointed out that there really isn't a particularly good place to go for this information. It occurred to me that, really, I had more or less picked up all of it by word of mouth and experience, and there just aren't any good reference sources on the topic. So… here's my word of mouth.

This is by no means a comprehensive gist. It's also important to understand that the techniques that I outline in here are not 100% absolute either. Performance on the JVM is an incredibly complicated subject, and while there are rules that almost always hold true, the "almost" remains very salient. Also, for many or even most applications, there will be other techniques that I'm not mentioning which will have a greater impact. JMH, Java Flight Recorder, and a good profiler are your very best friend! Mea

Thread Pools

Thread pools on the JVM should usually be divided into the following three categories:

CPU-bound
Blocking IO
Non-blocking IO polling

Each of these categories has a different optimal configuration and usage pattern.

	import com.dimafeng.testcontainers.PostgreSQLContainer
	import zio.blocking.{effectBlocking, Blocking}
	import zio.{Has, ZLayer, ZManaged}

	object TestContainer {
	type Postgres = Has[PostgreSQLContainer]

	def postgres(version: Option[String] = None): ZLayer[Blocking, Throwable, Postgres] =
	ZManaged.make {
	effectBlocking {

	{-# LANGUAGE DataKinds #-}
	{-# LANGUAGE PolyKinds #-}
	{-# LANGUAGE TypeOperators #-}
	{-# LANGUAGE UndecidableInstances #-}
	{-# LANGUAGE UnsaturatedTypeFamilies #-}

	import GHC.TypeLits
	import Prelude hiding (Functor, Semigroup)

	type Main = (Fizz <> Buzz) <$> (0 `To` 100)

	package fpmax

	import scala.util.Try
	import scala.io.StdIn.readLine

	object App0 {
	def main: Unit = {
	println("What is your name?")

	val name = readLine()

	# NVM
	curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.33.11/install.sh \| bash
	export NVM_DIR="$HOME/.nvm"
	[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
	[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion" # This loads nvm bash_completion
	nvm install 10

	# Yarn
	curl -o- -L https://yarnpkg.com/install.sh \| bash
	export PATH="$HOME/.yarn/bin:$HOME/.config/yarn/global/node_modules/.bin:$PATH"

	networking.networkmanager.fccUnlockScripts = [
	{id = "8086:7560"; path = "${pkgs.lenovo-wwan-unlock}/bin/fcc_unlock.sh";}
	];