Build Docker image only if Base Image has been modified since last build

Question

Let's say we have a dockerfile which contains a base image directive pointing to BaseImage:

FROM BaseImage
...

Is there any way so we can detect if BaseImage has been modified since the last build, so we can avoid building the image again?

score 0 · Answer 1 · answered May 31 '18 at 20:44

There was a previous question similar to this asking "How to automatically update your docker containers, if base-images are updated".

There is no standard way, but the user who answered (bsuttor) submitted the script he uses to check for updates to the base image in the Docker repo:

We use a script which checks if a running container is started with the latest image. We also use upstart init scripts for starting the docker image.

#!/usr/bin/env bash
set -e
BASE_IMAGE="registry"
REGISTRY="registry.hub.docker.com"
IMAGE="$REGISTRY/$BASE_IMAGE"
CID=$(docker ps | grep $IMAGE | awk '{print $1}')
docker pull $IMAGE

for im in $CID
do
    LATEST=`docker inspect --format "{{.Id}}" $IMAGE`
    RUNNING=`docker inspect --format "{{.Image}}" $im`
    NAME=`docker inspect --format '{{.Name}}' $im | sed "s/\///g"`
    echo "Latest:" $LATEST
    echo "Running:" $RUNNING
    if [ "$RUNNING" != "$LATEST" ];then
        echo "upgrading $NAME"
        stop docker-$NAME
        docker rm -f $NAME
        start docker-$NAME
    else
        echo "$NAME up to date"
    fi
done

And init looks like

docker run -t -i --name $NAME $im /bin/bash

Build Docker image only if Base Image has been modified since last build

1 Answers1