Another quick post.

What feels like a lifetime ago, I wrote a post about finding ec2 instances by name. I honestly use that script just about every day, mostly for automatically finding instances to SSH to (a la SSH config tricks). But there are a few other quick things I’ve done with it:

• ec2-script - Run a script on all instances of a given name
• ec2-disk - A specialization of ec2-script to check main disk usage
• terminate - A script that I use with ec2 to terminate instances from the command line
• ec2-cycle - Slow cycle a given set of ec2 instances by terminating so many per minute

All of which are included in my dotfiles.

ec2-script

Run a command on every instance returned by ec2:

#!/usr/bin/env fish

for ip in (ec2 $argv[1] --ips)
    echo $ip
    ssh ubuntu@$ip $argv[2..-1]
    echo
end

Mostly, this is a loop I write all the time, so it’s easier to wrap it in a script. I really do like fish scripting compared to bash. Slightly easier loops, more reasonable subshell syntax, and array slicing with better quoted argument behavior. Nice.

You can do some pretty powerful things with this:

$  ec2-script app-server 'sudo docker exec -dt `sudo docker ps | awk \'/app/ { print $1 }\'` python scripts/do-stuff.py'

For each instance, look at the running docker containers, get the one named app, and run a Python command in that container.

ec2-disk

Another specialization of the above:

#!/usr/bin/env fish

ec2-script $argv[1] 'df -h | egrep /$'

This is a one liner that will find the disk usage specifically of the root disk (the one who’s line ends with /).

terminate

This doesn’t directly use ec2, but I almost always call it as terminate (ec2 some-service --ip), so it might as well be:

#!/usr/bin/env fish

for ip in $argv
    set -lx instance_data (aws ec2 describe-instances --filters Name=private-ip-address,Values=$ip)
    set -lx instance_id (echo $instance_data | jq .Reservations[].Instances[].InstanceId | tr -d '"')
    if test "$instance_id" = ""
        echo "No instance found"
    else
        set -lx prompt "Terminate: $instance_id (name = "(echo $instance_data | jq -c '.Reservations[0].Instances[0].Tags[] | select(.Key == "Name") | .Value' | tr -d '"')") ? [y/N] "
        read -lp 'echo "$prompt"' confirm
        switch $confirm
            case Y y
                echo "Terminating $instance_id"
                aws ec2 terminate-instances --instance-ids $instance_id
        end
    end
end

You can of course do all of this with the built in aws CLI (I’m in fact doing eaxctly that), but remembering all that… nah.

ec2-cycle

Finally, something a bit different, a script to cycle a fleet of servers:

#!/usr/bin/env fish

if test (count $argv) -eq 1
    set name $argv[1]
    set time 60
else if test (count $argv) -eq 2
    set name $argv[1]
    set time $argv[2]
else
    echo "Usage: ec2-cycle {name} {time=60}"
    exit
end

echo "Cycling $name, waiting $time second(s) between each cycle"

for ip in (ec2 $name --ips)
    echo $ip
    yes | terminate $ip
    sleep $time
end

It uses terminate above, slow cycling instances 1 per every given number of seconds.