Dockerfile

FROM ruby:2.4

RUN gem install twitter
COPY rand_tweet.rb /
CMD ["ruby", "rand_tweet.rb"]

rand_tweet.rb

require 'twitter'

client = Twitter::REST::Client.new do |config|
  config.consumer_key        = ENV['consumer_key']
  config.consumer_secret     = ENV['consumer_secret']
  config.access_token        = ENV['access_token']
  config.access_token_secret = ENV['access_token_secret']
end
client.update(ENV['words'].split(',').sample)