`find_spec_for_exe': Could not find 'bundler' (2.1.4) required by your /var/app/ondeck/Gemfile.lock

Elastic Beanstalk 에 Rails application 을 디플로이하면 아래와 같은 에러 때문에 디플로이가 안될 때가 있다.

/opt/rubies/ruby-2.6.5/lib/ruby/site_ruby/2.6.0/rubygems.rb:284:in `find_spec_for_exe':
Could not find 'bundler' (2.1.4) required by your /var/app/ondeck/Gemfile.lock. (Gem::
GemNotFoundException)
To update to the latest version installed on your system, run `bundle update --bundler`.
To install the missing version, run `gem install bundler:2.1.4`
from /opt/rubies/ruby-2.6.5/lib/ruby/site_ruby/2.6.0/rubygems.rb:303:in `activate_bin_path'
from /opt/rubies/ruby-2.6.5/bin/bundle:23:in `<main>'.

Elastic Beanstalk Ruby instance 에서 기본 사용하는 bundler 가 실행하려는 ruby application 이 필요로하는 bundler 버전과 맞지 않아서 발생하는 문제다.

.ebextensions/gem_install_bundler.config 스크립트를 아래와 같이 생성한 후 다시 디플로이한다. 

commands:
  update_bundler:
    command: /opt/rubies/ruby-2.6.5/bin/gem install bundler -v 2.1.4
files:
  # Runs before `./10_bundle_install.sh`:
  "/opt/elasticbeanstalk/hooks/appdeploy/pre/09_gem_install_bundler.sh" :
    mode: "000775"
    owner: root
    group: users
    content: |
      #!/usr/bin/env bash

      EB_APP_STAGING_DIR=$(/opt/elasticbeanstalk/bin/get-config container -k app_staging_dir)
      EB_SCRIPT_DIR=$(/opt/elasticbeanstalk/bin/get-config container -k script_dir)
      # Source the application's ruby, i.e. 2.6. Otherwise it will be 2.3, which will 
      give this error: `bundler requires Ruby version >= 2.3.0`
      . $EB_SCRIPT_DIR/use-app-ruby.sh

      cd $EB_APP_STAGING_DIR
      echo "Installing compatible bundler"
      gem install bundler -v "$(grep -A 1 "BUNDLED WITH" Gemfile.lock | tail -n 1)"
      gem update --system