The AWS Elastic BeanStalk Documentation specifically wrote:
Elastic Beanstalk currently supports the following package managers: yum, rubygems, python, and rpm.
So, what should I do if I want to install some packages on an Ubuntu image?
Can I replace
rpm lines with
packages: yum: libmemcached:  ruby-devel:  gcc:  rpm: epel: http://download.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm rubygems: chef: '0.10.2' apt: mysql-client: 
(I cannot find explanation about the
apt: section in the AWS Documentations, though.)