A script to remove all but the latest version of all lambda functions found in a stack.

0. Deleting lambda versions.md

Deleting old lambda versions

Tip

Serverless Land offers a Lambda function cleanup step-function pattern, which can also help you to manage steady accumulation of lambda versions.

This script fills a similar niche. It will review a CloudFormation stack and remove all but the most recent N versions of all versioned lambda functions it finds there.

Context

If you have enabled Lambda versioning for your AWS deployment (perhaps because you want to be able to use Lambda SnapStart to reduce some inconveniently long cold-start times for certain runtimes, or maybe because you want to control version updates), you may be surprised to discover that all your lambda versions are preserved ad-inifinitum, and that there's no automated mechanism to delete older versions, or to set an expiry time for them.

Caching: For every function version that you publish with SnapStart enabled, you pay for the cost of caching and maintaining the snapshot.

This is especially problematic if you are using SnapStart because you may be charged for every snapshot held by SnapStart for every version of every lambda you have published. (NB. Java does not incur an additional cost.) These are also held ad-inifinitum (and do not fall under free usage levels!)

Usage

remove-old-lambda-versions.sh --stack <stack-name> [--region <region>] [--keep <keep>] [--delete]

• <stack-name> the name of your stack (required)
• <region> the AWS region to use (defaults to eu-west-2)
• <keep> the number of most recent versions of the lambda to keep

The script will perform a dry run (ie. it won't delete anything) unless you also provide the -y/--delete parameter.

remove-old-lambda-versions.sh

#!/bin/bash

usage() {
  cat << EOF

Deletes all versions (except the N latest), of lambda functions belonging to a stack.
This script will only perform deletions if the -y/--delete option is set.

Options:
    -s <name>      --stack <name>                  Sets the name of the stack (required)
    -r <region>    --region <region>               Sets the AWS region (default: eu-west-2)
    -k <number>    --keep <number>                 Number of versions to keep (default: 1)
    -y             --delete                        Set to delete lambda versions (default: not set)
    -h             --help                          Prints this help message and exits

EOF
}

# prevent paging - useful for running in automated pipelines
export AWS_PAGER=""

# defaults
REGION=eu-west-2
KEEP_VERSIONS=1
DO_IT="false"

# parameters
while [ -n "$1" ]; do
  case $1 in
  -s | --stack)
    shift
    STACK_NAME=$1
    ;;
  -r | --region)
    shift
    REGION=$1
    ;;
  -k | --keep)
    shift
    KEEP_VERSIONS=$1
    ;;
  -y | --delete)
    DO_IT="true"
    ;;
  -h | --help)
    usage
    exit 0
    ;;
  *)
    echo -e "Unknown option $1...\n"
    usage
    exit 1
    ;;
  esac
  shift
done

if [ -z "$STACK_NAME" ]; then
  echo "Please specify a stack name."
  usage
  exit 1
fi

echo "Region: $REGION"
echo "Stack:  $STACK_NAME"
echo "Keep:   $KEEP_VERSIONS"
echo "Delete: $DO_IT"
echo

# iterate through all stacks related to the named stack
for STACK in $(aws cloudformation list-stacks \
  --region $REGION \
  --output text \
  --query "StackSummaries[?contains(StackName, '${STACK_NAME}') && (StackStatus=='CREATE_COMPLETE'||StackStatus=='UPDATE_COMPLETE')].[StackName]")
do
  echo "Stack: $STACK..."
  echo

  NEXT_TOKEN=""
  FETCH_MORE_STACK_RESOURCES="true"
  while [ "$FETCH_MORE_STACK_RESOURCES" == "true" ]
  do
    STACK_RESOURCES=$(aws cloudformation list-stack-resources \
      --stack-name $STACK \
      --region $REGION \
      ${NEXT_TOKEN:+--starting-token "$NEXT_TOKEN"} \
      --output json)

    FUNCTION_IDs=$(echo $STACK_RESOURCES | jq -r '.StackResourceSummaries[] | select(.ResourceType=="AWS::Lambda::Function") | .PhysicalResourceId')
    for FUNCTION_ID in $FUNCTION_IDs
    do
      FUNCTION_NAME=$(echo $STACK_RESOURCES | jq -r '.StackResourceSummaries[] | select(.PhysicalResourceId=="'$FUNCTION_ID'") | .LogicalResourceId')
      echo " - Function: $FUNCTION_NAME"
      
      VERSION_NUMBERS=$(aws lambda list-versions-by-function --function-name $FUNCTION_ID --region $REGION --output json \
        | jq -r '.Versions[] | .Version' \
        | grep -wv '$LATEST' \
        | sort -nr)

      KEEPING=$(echo "$VERSION_NUMBERS" | head -n $KEEP_VERSIONS)
      DELETING=$(echo "$VERSION_NUMBERS" | tail -n +$((KEEP_VERSIONS+1)))

      for KEEP_VERSION_NUMBER in $KEEPING
      do
        echo "   - keeping version: $KEEP_VERSION_NUMBER"
      done
      for DELETE_VERSION_NUMBER in $DELETING
      do
        if [ "$DO_IT" == "true" ]; then
          echo "   - deleting version: $DELETE_VERSION_NUMBER"
          aws lambda delete-function --function-name $FUNCTION_ID --region $REGION --qualifier $DELETE_VERSION_NUMBER
        else
          echo "   - would delete version: $DELETE_VERSION_NUMBER"
        fi
      done
      echo
    done # current page of stack resources

    # check for more resources...
    NEXT_TOKEN=$(echo $STACK_RESOURCES | jq -r '.NextToken')
    echo "Next token: $NEXT_TOKEN"
    if [ -z "$NEXT_TOKEN" ] || [ "$NEXT_TOKEN" == "null" ]; then
      FETCH_MORE_STACK_RESOURCES="false"
    fi
    echo "Fetch more: $FETCH_MORE_STACK_RESOURCES"
    echo
  done

done # all stacks