Configure Dockerfile to Run Cron Tasks using Whenver and Rake

Question

I want to create a container using Docker which is will be responsible for starting recurrent rake tasks based on the Whenever gem's configuration. I have a plain ruby project (without rails/sinatra) with the following structure:

Gemfile:

source 'https://rubygems.org'
gem 'rake', '~> 12.3', '>= 12.3.1'
gem 'whenever', '~> 0.9.7', require: false
group :development, :test do
  gem 'byebug', '~> 10.0', '>= 10.0.2'
end
group :test do
  gem 'rspec', '~> 3.5'
end

config/schedule.rb: (whenever's configuration)

ENV.each { |k, v| env(k, v) }
every 1.minutes do
  rake 'hello:start'
end

lib/tasks/hello.rb: (rake configuration)

namespace :hello do
  desc 'This is a sample'
    task :start do
    puts 'start something!'
  end
end

Dockerfile:

FROM ruby:2.5.3-alpine3.8

RUN echo "http://dl-cdn.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories && \
    apk update && apk upgrade && \
    apk add build-base bash dcron && \
    apk upgrade --available && \
    rm -rf /var/cache/apk/* && \
    mkdir /usr/app

WORKDIR /usr/app

COPY Gemfile* /usr/app/

RUN bundle install

COPY . /usr/app

RUN bundle exec whenever --update-crontab

CMD ['sh', '-c', 'crond && gulp']

I've used the following resources to get at the this point

How to run a cron job inside a docker container
https://github.com/renskiy/cron-docker-image/blob/master/alpine/Dockerfile
https://stackoverflow.com/a/43622984/5171758 <- very close to I want but no success

If I call my rake task using command line, I get the result I want.

$ rake 'hello:start'
start something!

However, I can't figure out how to make it work using Docker. The container is build but no log is written, no output is shown, nothing happens. Can someone help me showing what I'm doing wrong?

building commands

docker build -t gsc:0.0.1 .
docker container run -a stdin -a stdout -i --net host -t gsc:0.0.1 /bin/bash

Thanks all. Cheers

That CMD doesn’t look like what you want; the way you describe your setup you don’t need a cron daemon at all. — David Maze, Dec 06 '18 at 14:45
@DavidMaze what is your suggestion to an image which will call the rake tasks? I don't see the mistake you've pointed out. — tiagomenegaz, Dec 06 '18 at 14:47
The `config/schedule.rb` seems like it would replace a cron daemon (the mention of gulp, a JavaScript build tool, is a little odd too). I’d expect to see some mention of `whenever` if that’s the tool you’re using. — David Maze, Dec 06 '18 at 14:49
@DavidMaze I mention whenever at the before last line of the Dockerfile. I think I understood what you mean. I'll give it a go — tiagomenegaz, Dec 06 '18 at 14:57
Another solution is to use the gem [arask](https://github.com/Ebbe/arask) for recurring tasks. Nothing to setup in docker. You just need to start rails. — Esben Damgaard, Jan 25 '19 at 14:06
@EsbenDamgaard That might be a good solution for a rails application. In my case, I have a ruby project. No framework is used. — tiagomenegaz, Feb 07 '19 at 02:16

tiagomenegaz · Accepted Answer · 2019-03-07T04:48:21.053

This is the solution to the problem I listed above. I had some issues at the Dockerfile and schedule.rb. This is what I had to change to make it work correctly.

Dockerfile

wrong echo call
wrong bundle command
change ENTRYPOINT instead of CMD

FROM ruby:2.5.3-alpine3.8

RUN apk add --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/main && \
    apk update && apk upgrade && \
    apk add build-base bash dcron && \
    apk upgrade --available && \
    rm -rf /var/cache/apk/* && \
    mkdir /usr/app

WORKDIR /usr/app

COPY Gemfile* /usr/app/

RUN bundle install

COPY . /usr/app

RUN bundle exec whenever -c && bundle exec whenever --update-crontab && touch ./log/cron.log

ENTRYPOINT crond && tail -f ./log/cron.log

config/schedule.rb

no need to ENV.each

every 1.minutes do
  rake 'hello:start'
end

UPDATE

I've created a GitHub repository and a Docker Hub repository to share with the community this progress.

Configure Dockerfile to Run Cron Tasks using Whenver and Rake

1 Answers1