peterwwillis

Run commands

Use Docker to build a Jenkins plugin

1. Check out a Jenkins plugin from GitHub

   $ git clone git@github.com:jenkinsci/configuration-as-code-secret-ssm-plugin.git
   $ cd configuration-as-code-secret-ssm-plugin

2. Build the plugin. Change the maven tag to something like 3-jdk-8 or 3-jdk-11 if you run into errors, as some plugins only build with one JDK version.
   • Run as a non-root user

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Tips and Best Practices for programming in C

Syntax

Tips

• You can explain a complicated declaration in English using cdelc.
  • echo "explain char *(*pfpc)()" | cdecl
  • https://cdecl.org/

Data Structures / Types

peterwwillis

Set up Ubuntu Linux to use Active Directory for user authentication + authorization

This guide will step you through setting up an Ubuntu 18.04 Linux system so that you can login to it using an Active Directory server for authentication and authorization. NOTE: You do not need to join a domain to use this method!!

The net effect of this guide is that you do not need to ever set up a user on your Linux host. Its home directory will be automatically created at log-in time, and its password is checked (along with account expiration) against the Active Directory server.

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If you try to copy a source directory into a symlink to a target directory, you may get an error like: cp: cannot overwrite non-directory 'symbolic-link' with directory 'source'.

The solution is to actually copy the . directory of your source directory. This is not obvious based on the GNU coreutils FAQ or the man page.

Below is an example to explain:

vagrant@devbox:~/foo$ mkdir bin

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Awk

Print only the first part of a file separated by two newlines

Note that this uses tr to remove any carriage-returns (as in "\r\n" from Windows or network programs)

# Print only the block of lines before the first double-newline
cat file.txt | tr -d '\r' | \
  awk 'BEGIN {RS="\n\n"} NR==1'
 

peterwwillis

Package Management is Inherently Dumb

All packaged software is just a random person trying to guess at how to install and run some random software. The package has to declare what packages it depends on, and what it conflicts with.

The only way for a package to have the correct 'depends' and 'conflicts' is for the original software to ship with an explicit map of all its dependencies and conflicts. No software does this, in part because every Linux distribution ships different packages, and thus has different dependencies and conflicts. And so, we have to build packages by hand. A human (who isn't the software developer) has to determine the correct dependencies and conflicts (based on other packages that this human also did not create). Then they need to build the package and test it.

A package manager (dpkg) is a dumb program that does whatever you tell it to do. A package encodes its own dependencies, and the package manager fulfills the requirements as stated, or fails if it's impossible. There's n

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# This Makefile allows you to pass arguments to 'make', and have those get passed into commands for a target.
# This also shows how to automatically generate a help menu using specially annotated comments on targets.
# 
# Usage:
#   - make help
#         List of available targets:
#         
#          help              List all available targets (default)
#          jenkins-cluster   Run terraformctl on the aws-jenkins-cluster root module
#          cognito-userpool  Run terraformctl for the cognito user pool

peterwwillis

Install Certbot

Debian 8

Debian 8 (Jessie) End Of Life was June 17, 2018, its LTS support ended on June 30, 2020, and its Extended LTS ends on June 30, 2022. The backports have been moved to "archive", so extra steps are necessary to install backport packages.

echo "deb [check-valid-until=no] http://archive.debian.org/debian jessie-backports main" > /etc/apt/sources.list.d/jessie-backports.list
apt-get -o Acquire::Check-Valid-Until=false update
apt-get -o Acquire::Check-Valid-Until=false -t jessie-backports install -y certbot

peterwwillis

How to make Hacker News resistant to outages

This is an explanation of how Hacker News could be made resilient against network and infrastructure failures.

Step 1. DNS redundancy

Make sure you use a DNS nameserver provider that has multiple nameservers using multiple cloud hosting providers in multiple regions and zones. For added redundancy, use multiple nameserver providers, replicate your records between them, and make sure each uses different providers/regions.

Point your origin DNS record (origin.mydomain.com) at each of your origins, using CNAMEs or A records. Keep the TTL as low as you can, usually 60 seconds. Since only your CDN should be hitting this host, this shouldn't stress your nameserver. During an outage, one origin can be removed from DNS (if necessary).

peterwwillis

The difference between configuration formats, configuration languages, data formats, and programming languages

There is a lot of confusion out there about what different file formats are and how they are intended to be used. Having used a lot of them over the years, I think I can explain their differences, and when and how to use them.

Data formats

A data format is a file format for encoding data. Typically the format is structured to make it easier for machine interpreting & processing.