Delete Launch Config Programatically – AWS

To delete launch config in AWS programatically is something I left out in one of my previous posts – Scaling WordPress in Amazon Cloud. In that post I explained how I create an AMI snapshot of a WordPress instance after each deployment. This ensures that I have an up to date AMI (frozen pizza model) to spin up when I need to scale horizontally. However, every time I create a new AMI I need to create a new launch configuration and update the existing auto scaling group with it. That leaves a handful of old launch configurations that can pile up unnecessarily in your AWS account. At the time of writing this post, AWS has a limit of 100 launch configurations, after which creating new ones is not possible. To prevent your account from accumulating all these unnecessary launch configs, you can write a cron job that will cleanup your configs nightly.

This particular bash script does the job for me:

Delete Launch Config Programatically

For this script to work you will need to install and configure the following tools:

  1. AWS CLI
  2. JQ (lightweight command line JSON processor)

export AWS_CONFIG_FILE=/root/awsconfig
export PATH=$PATH:/usr/local/bin

# Check if a value exists in an array
# @param $1 mixed  Needle  
# @param $2 array  Haystack
# @return  Success (0) if value exists, Failure (1) otherwise
# Usage: in_array "$needle" "${haystack[@]}"
# See:
in_array() {
    local hay needle=$1
    for hay; do
        [[ $hay == $needle ]] && return 0
    return 1

# Get all launch configuration names that have been created for this AWS account
allconfigs=$(aws autoscaling describe-launch-configurations | jq '.LaunchConfigurations[].LaunchConfigurationName' | sed s/\"//g)

# Get all active launch configurations names that are currently associated with running instances 
allinstances=$(aws autoscaling describe-auto-scaling-instances | jq '.LaunchConfigurations[].LaunchConfigurationName' | sed s/\"//g)

# Get all active launch configuration names that are currently associated with launch configuration groups
allgroups=$(aws autoscaling describe-auto-scaling-groups | jq '.LaunchConfigurations[].LaunchConfigurationName' | sed s/\"//g)

# merge group configs and active instances configs into one array.  We need to keep them, and remove the rest
groupsandinstances=(`for R in "${instances[@]}" "${groups[@]}" ; do echo "$R" ; done | sort -du`)

#Loop through all configs and check against active ones to determine whether they need to be deleted
for i in "${configs[@]}"
        #echo $i
        in_array $i "${groupsandinstances[@]}" && echo active ${i} || echo deleting ${i} `aws autoscaling delete-launch-configuration --launch-configuration-name ${i}`

Now you can set up this script to run nightly at, say, 3:30am. To do that you simply create a cron job:

sudo nano /etc/cron.d/cleanup_launch_configs
# Cleanup Launch configs that are generated by deployment procedures
30 3 * * * root /path_to_your/

As always, before you implement this in your production environment test it out thoroughly and make sure you understand what you’re doing.