DEV Community: Garett Dunn

AWS EC2 - Limit an Instance's Access to its Own Tags

Garett Dunn — Thu, 20 Aug 2020 00:00:00 +0000

Here’s a dynamic way to allow an EC2 instance to modify its own tags, but no other instance’s. Enjoy.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": ["ec2:CreateTags", "ec2:DescribeTags"],
      "Resource": "*",
      "Condition": {
        "StringEquals": {
          "aws:ARN": "${ec2:SourceInstanceARN}"
        }
      }
    }
  ]
}

Liberate Orphaned OpenStack Volumes

Garett Dunn — Fri, 28 Jun 2019 19:12:52 +0000

If you delete a server that a volume is attached to, and then quickly try to delete the volume before the server has finished deleting (at least, that’s where I think the problem stems from; it could just be that this happens even if you waited for it to fully delete), the volume can get stuck saying that it’s still attached. You cannot run openstack server remove volume <server id> < volume id> because it will complain that the server doesn’t exist. The only way I could figure out how to get around this is to use the cinder tool to remove the attachement ID

openstack volume show <volume_id>
# Grab the attachment ID for use in next step

cinder --os-volume-api-version 3.50 attachment-delete <attachment_id>
# For some reason you have to specify at least api version 3.50. Why it can't figure this out on it's own is beyond me

Hopefully this will help someone out.

Brewlette - Discover homebrew packages

Garett Dunn — Tue, 11 Jun 2019 14:26:00 +0000

I'm kind of OCD about keeping packges updated, maybe to a fault. One result of this obsession is that I run brew update every morning on my Mac. This command updates the list of packages, even ones you don't use, so after running it you're presented with a list of all sorts of packages. If I'm not in a hurry, I'll usually spot 1 or 2 packages that sound interesting, and might end up installing them. After doing this for a while, I decided that it would be cool if I could just issue a command and get a random package at will. Turns out this is actually easy to do.

Without further ado, I present: brewlette!

$ brewlette

Try out a random homebrew package!

flvmeta: stable 1.2.1 (bottled), HEAD
Manipulate Adobe flash video files (FLV)
https://www.flvmeta.com/
Not installed
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/flvmeta.rb
==> Dependencies
Build: cmake ✔
==> Options
--HEAD
    Install HEAD version

Command "brew install flvmeta" copied to clipboard

Really, it's just a simple shell script that I put in /usr/local/bin (where brew usually installs packages). It works by picking a random package from the list of formulas that brew caches. One little nifty addition I made is that it copies the brew commmand to install the package to your clipboard. Just ⌘+v and enjoy the new package. For now the script is on a Github gist. Feel free to comment/fork if you want to make a contribution. Here's the script:

#!/usr/bin/env bash
# Utility to suggest a new package to try from Homebrew
# Simply run and it will give you a new package to try out

files=(/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/*)
total=${#files[@]}
rando=$((RANDOM % total))
package=$(basename "${files[rando]}" .rb)
printf "\\nTry out a random homebrew package!\\n\\n"
brew info "${package}"

if [[ $(command -v pbcopy) ]]
then
    echo "brew install ${package}" | pbcopy
    printf "\\nCommand \"brew install %s\" copied to clipboard\\n" "$package"
else
    printf "\\nUse \"brew install %s\" to try it out\\n" "$package"
fi

Unset All Variables Matching a Pattern

Garett Dunn — Tue, 02 Apr 2019 01:04:30 +0000

Unset all variables beginning with prefix

When using the Openstack CLI, you typically will get a shell script that you would source, which will export a bunch of variables to your session. I’ve run into the problem of switching between two different Openstack installs that were on different versions, and needed different variables. I had issues where variables from one instance were still there when trying to use another one. I could go ahead and remove them one by one, but I didn’t get into this line of work to do things by hand. Accordingly, the following example will unset all Openstack variables (all variables that begin with OS_)

For bash it’s

# Bash
unset "${!OS_@}"

Because it’s bash, it’s a cryptic incantation of symbols that only wizened old graybeards can explain. (that's sarcasm)

For zsh it’s

# zsh
unset -m "OS_*"

As you can see, in zsh it’s much simpler. You use the -m flag (I believe it stands for “match”) then use a glob match. I’m not sure if it supports regex or not, because for some reason the documentation for zsh builtins is not easy to find.

Obviously, you can use this for a lot of things. I tend to use this a lot with CLI tools (Openstack, AWS, Terraform, etc). Hopefully it’s useful for you!