Detect updates to the Docker base image

detect-updates-to-the-docker-base-image.sh

#!/bin/bash

REQUIRED_COMMANDS=("skopeo" "jq" "basename")

for COMMAND in "${REQUIRED_COMMANDS}"; do
    if ! command -v ${COMMAND} > /dev/null; then
        echo "Error: ${COMMAND} command is required." 1>&2
        exit 2
    fi
done

if [ $# -ne 2 ]; then
    echo "Usage: $(basename $0) BASE_IMAGE_NAME:TAG IMAGE_NAME:TAG"
    exit 2
fi

BASE_CONTAINER=$1
TARGET_CONTAINER=$2

BASE_JSON=$(skopeo inspect --config docker://${BASE_CONTAINER})
[ $? -eq 0 ] || exit 1
TARGET_JSON=$(skopeo inspect --config docker://${TARGET_CONTAINER})
[ $? -eq 0 ] || exit 1
BASE_LAYER_ID=$(echo ${BASE_JSON} | jq "(.rootfs.diff_ids | reverse)[0]")
FOUND_LAYER_ID=$(echo ${TARGET_JSON} | jq ".rootfs.diff_ids[] | select(. == ${BASE_LAYER_ID})")

if [ "${BASE_LAYER_ID}" != "${FOUND_LAYER_ID}" ]; then
    echo "The Docker image needs to be updated."
    echo "- ${TARGET_CONTAINER}"
    echo "  |- ${BASE_CONTAINER}  [newer version found]"
    echo ""
    exit 1
fi