BaseImages – with and without pre-installed OpenJDK

The JDK-including images built by this repository rely on Eclipse Adoptium Temurin OpenJDK, which is the rebranded Adopt OpenJDK since July 2021.

Just another repository with Docker image definitions

This repository is meant to host Java-Applications – separated by branches:

• the master contains the “base image” with basic toolings and Java installation.
• all other branches are meant to host separate applications – as long as the branch name was added as a key of an empty dictionary to built.json.

built.json – information and definition file

The file built.json is a JSON file containing a dictionary of dictionaries.
The first level of keys is meant to define the branches reflected. If the master is removed for any reason, it will be re-added automatically. Every other branch will stay removed won’t build anymore.

{
    "master": {
        "jdk8": "YYYY-MM-DD HH:ii:ss",
        "jdk11": "YYYY-MM-DD HH:ii:ss",
        "jdk17": "YYYY-MM-DD HH:ii:ss",
        "latest": "YYYY-MM-DD HH:ii:ss"
    },
    "application": {
        "tag": "YYYY-MM-DD HH:ii:ss"
    }
}

The workflow directory

The workflow directory is important on every active branch, since the files there define the building-process during the Github workflow. That’s described below more in detail.

Useful File Locations

• /certs - location for custom certificates

environmental variables

env	default	change recommended	description
EDITOR	vim	yes	Default editor for the container – there are multiple ones installed like vim (default) and nano.
TIMEZONE	Europe/Berlin	yes	Timezone used within container – adjust to where you are living
SET_LOCALE	de_DE.UTF-8	yes	Default locale used for keyboard layout selection, etc – not always relevant within containers, but sometimes very usefull
START_CRON	0	yes	Should cron be started within the container? Then set it to 1.
BOOT_MSG_SHOW	1	yes	Should messages of boot.sh sourced scripts be shown? Then 1 is perfect, otherwise change to 0.
CRON_PATH	/etc/cron.d/docker	no	Where is the cron file located? for information about the cron file, see below.
CUSTOM_CERTS_PATH	/certs	no	Location where to find custom certificates which will be imported and trusted – useful to accept custom (selfsigned) RootCAs.
TERM	xterm	no
DEBIAN_FRONTEND	noninteractive	no

build variables

There are also some special variables, that are only used during build process of the docker image:

variable name	type	value	description
IMAGE	ARG	ubuntu	The docker images built within this repository are built on official docker library version of Ubuntu.
VERSION	ARG	20.04	We relay on the LTS releases of Ubuntu for docker images built through this repository.
JDK_NAME	ENV	temurin-17-jdk	Temurin JDK to be installed. For the latest tag, no JDK will be installed.

By using the different types of environmental variables within the image build and usage process, we assure them being available in relevant contexts.
Docker uses build arguments (type ARG) for environmental variables only available during the build process of an image. ENV type variables are available in both contexts, during the build and when running a container from the image.

Cron-File

# This crontab file holds commands for all users to be run by
# cron. Each command is to be defined within a separate line.
#
# To define the time you can provide concrete (numeric) values,
# comma separate them or use \`*\` to use any of the possible
# values.
# You can also use basic calculation - i.e. if you want to run
# a job every 20th minute use \`*/20\`.
#
# The tasks will be started based on the system time and
# timezone.
#
#
# The example below would print a message to the STDOUT of the
# docker container and - if any error does occur – the errors
# will be printed to the STDERR of the container.
#
# Please be aware that you are locating the crontab file within
# \`/etc/cron.d\` directory and for that there is also the need
# to define the user who should run the cron command!
#
# ┌────────────────────────────────── minute (0-59)
# │    ┌───────────────────────────── hour (0-23)
# │    │    ┌──────────────────────── day (1-31)
# │    │    │    ┌─────────────────── month (1-12)
# │    │    │    │    ┌────────────── day of week (0-6, sunday equals 0)
# │    │    │    │    │    ┌───────── user
# │    │    │    │    │    │    ┌──── command
# │    │    │    │    │    │    │
# ┴    ┴    ┴    ┴    ┴    ┴    ┴
# */20 *    *    *    *    root echo 'this is a demonstration cronjob'  1> /proc/1/fd/1  2> /proc/1/fd/2

License

This project is published under the CC BY-SA 4.0 license.