Container Init

At times, we think if only this container acted a little different that its normal.

say for example:

• we need to change the default user defined in dockerfile but at the same time we don't want to rebuild the dockerimage.
• install new packages in a docker image, yet we don't want to build a new image using the source of the original docker image.
• sometimes when you are lazy and you want to directly manipulate a docker image

The Script

Then you may need "con-init" or coninit.sh a.k.a "Container Init"

This is a coninit.sh for alpine linux based containers.

#!/bin/bash

CUID=1000
CGID=1000
USERNAME=anish

#install dependencies
apk update
apk add shadow sudo bash curl yarn jq

#Create User and Groups and Sudo Access
groupadd -g ${CGID} ${USERNAME}
useradd ${USERNAME} -u ${CUID} -g ${CGID} -m -s /bin/bash
usermod -a -G wheel ${USERNAME}
echo "${USERNAME} ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers.d/${USERNAME}

#Run infinitely
tail -f /dev/null

If we are using a debian/ubuntu container then the above (for alpine) won't work as expected. So in case of Debian based containers use below.

#!/bin/bash

CUID=1000
CGID=1000
USERNAME=anish

#install dependencies
apt update
apt install -y passwd sudo bash curl jq vim-tiny git

#Create User and Groups and Sudo Access
groupadd -g ${CGID} ${USERNAME}
useradd ${USERNAME} -u ${CUID} -g ${CGID} -m -s /bin/bash
UID_MAX=500000000 usermod -a -G adm,sudo ${USERNAME}
echo "${USERNAME} ALL=(ALL) NOPASSWD:ALL" >>/etc/sudoers.d/${USERNAME}

#Run infinitely
tail -f /dev/null

The Compose file

Now to use this coninit.sh we wil employ a docker-compose.yml file as below:

version: '3.8'
services:
  node-dev:
    image: node:16.16.0-slim
    container_name: node-dev
    working_dir: /srv
    environment:
      - VAR1="Foo"
      - VAR2="Bar"
    volumes:
      - ./con-init.sh:/root/con-init.sh
      - ./app:/srv
    command: sh /root/con-init.sh

Create a empty directory named "app" in the same directory which houses docker-compose.yml file.

you can put the code files in the newly created "app" directory.

Then do:

docker-compose up -d

now a new container named node-dev with start using the node:16.16.0-slim image with the changes we added in the coninit.sh file.

Now lets connect to the new container, assuming we created the user as anish in the coninit.sh file. If you used a different user replace anish with the username you used in the below command.

docker-compose exec -u anish -it node-dev /bin/bash