Install cron in docker container based on Ruby

General Discussions General
#1

Good day. I would like to use the whenever gem for my ruby on rails project. However, I discovered that crontab command is not found on my container. I used apt-get install cron but it returns Unable to locate package cron
Below is my Dockerfile and docker-compose file.

Dockerfile

FROM ruby:2.4

RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        postgresql-client build-essential libpq-dev nodejs \
    && rm -rf /var/lib/apt/lists/*

RUN touch /var/log/cron.log

RUN apt-get -y install cron

WORKDIR /src/tmp
COPY Gemfile* ./
RUN gem install bundler
RUN bundle install
VOLUME /source

EXPOSE 3000
CMD ["bash"]

docker_compose.yml

version: '2.1'
services:
  legacy:
    image: mysql
    env_file: ./docker.env
    volumes:
      - ../mydump:/docker-entrypoint-initdb.d
      - ../mycache:/var/lib/mysql
  db:
    image: postgres
    env_file: ./docker.env
  web:
    build: .
    command: bash
    volumes:
      - .:/source
    ports:
      - "3000:3000"
    depends_on:
      - db
      - legacy
    links:
      - db
      - legacy
    tty: true
    env_file: ./docker.env

I also tried including the installation in the Dockerfile but the build process halted because of the error in installing cron. Any suggestions on how to fix this? Thank you very much.

P.S. I execute the installation after running bash for the container.

#2

Sorry. Just figured out that the solution was simple. Needed to ran apt-get update. A bit confused why it’s the case since it’s already executed in the dockerfile but anyway, if this bears no significant contribution, please delete this post. Thank you.

#3

I would suggest to start using other scheduling mechanism.

You would need other tools like redis and so on, but this would work better.

Ruby has gems like sidekiq and other plugins to enable scheduled task to be run.