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Dockerize your own image

Jorge Aguilera, jorge.aguilera@puravida-software.com

Descargar el script ../scripts/docker/WatchFile.groovy

14 October 2017

In a previous post (Docker and Groovy) we reviewed how can we use the official image of Groovy to execute our scripts into the container where is running. Also with these images we can use all features of Docker as mount volumes, networking etc and in this way our scripts can works together with others containers.

In this post we’ll see how can use these images to build our own image and upload them to our account in Docker Hub, private Nexus, Google, etc

We’ll use a simple script to dump a file to console every 30 seconds in a forever while

WatchFile.groovy
if( !args.size() ){
	println "necesito un fichero que vigilar"
	return
}

while( true ){
	File f = new File(args[0])
	f.eachLine{ line ->
	   println line
	}
	sleep 30*1000
}
INFO

As you can see in this post the script is not the mos important

Dockerfile

First of all we need to write an instructions file Dockerfile to send to Docker. The name can be whatever you want but usually it’s Dockerfile

FROM groovy:2.4.12-jre8-alpine

COPY WatchFile.groovy /home/groovy/

VOLUME ["/var/watchfile"]

ENTRYPOINT ["groovy", "WatchFile.groovy"]

CMD []

We are instructing to Docker who image we can use as base (*groovy:2.4.12-jre8-alpine), we add a file from our filesystem and we specify we want to execute a command at the startup of the container ( groovy WatchFile.groovy).

If we run the scripts without parameters it can show us instructions or whatever you want. Or you can specify a defaul action using CMD []

Our image will be mount a volume in /var/watchfile. In this way our script will be able to read files from others containers or a subdirectory into the host system and dump it

Building the image

From the directory where we have both files we execute:

docker build --rm -t jagedn/watchfile .  //(1)

  1. jagedn/watchfile will be the name of our image. Be aware of the dot at the end

If all works fine you’ll have into your system a jagedn/watchfile image.

Check it with:

docker images | grep jagedn

Run a container

This is an example of how to run a container with this image:

docker run --rm -it -v /foo/baar:/var/watchfile jagedn/watchfile /var/watchfile/mifichero.log //(1)

  1. /foo/baar is a subdirectory into your machine with a file named mifichero.log

Every 30 seconds you will see a dump of the file in the console. You can modify mifichero.log and you’ll see in the next iteraction the changes

As you can see this example is not very interesting but you can see the steps to have your script dockerized. Rembember to execute the push if you want to upload the image to the repository:

docker push jagedn/watchfile
Script
if( !args.size() ){
	println "necesito un fichero que vigilar"
	return
}

while( true ){
	File f = new File(args[0])
	f.eachLine{ line ->
	   println line
	}
	sleep 30*1000
}