Default dockerfile template adds additional size to image.

[m2dc0d3r]

I'm not sure this issue has been already reported but there are some parts in docker.rb that needs a change.
https://github.com/test-kitchen/kitchen-docker/blob/master/lib/kitchen/driver/docker.rb
there are RUN commands to install openssh-server and some additional tools.
in the end there always should be a command to clear up the package manager cache.
For example:
when 'rhel', 'centos', 'fedora'
<<-eos
ENV container docker
RUN yum clean all
RUN yum install -y sudo openssh-server openssh-clients which curl
RUN [ -f "/etc/ssh/ssh_host_rsa_key" ] || ssh-keygen -t rsa -f /etc/ssh/ssh_host_rsa_key -N ''
RUN [ -f "/etc/ssh/ssh_host_dsa_key" ] || ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key -N ''
eos
RUN yum install -y sudo openssh-server openssh-clients which curl;yum -y clean all
This i a run without yum cache clean:
IMAGE CREATED CREATED BY SIZE COMMENT
88057ecdce48 5 minutes ago /bin/sh -c echo ssh-rsa\ AAAAB3NzaC1yc2EAAAA… 400B
0b219bed0d9f 5 minutes ago /bin/sh -c yum -y install net-tools iproute … 27.3MB
3a1ee7b87743 5 minutes ago /bin/sh -c chmod 0600 /home/kitchen/.ssh/aut… 0B
579e3edae0ec 5 minutes ago /bin/sh -c chown kitchen /home/kitchen/.ssh/… 0B
ac6eb1169c96 5 minutes ago /bin/sh -c touch /home/kitchen/.ssh/authoriz… 0B
211d693a52a8 5 minutes ago /bin/sh -c chmod 0700 /home/kitchen/.ssh 0B
b5e303c0d289 5 minutes ago /bin/sh -c chown -R kitchen /home/kitchen/.s… 0B
d1b2bd9ef6d1 5 minutes ago /bin/sh -c mkdir -p /home/kitchen/.ssh 0B
d081ad9852f8 5 minutes ago /bin/sh -c echo "Defaults !requiretty" >> /e… 3.99kB
6f3e8bfcfa64 5 minutes ago /bin/sh -c echo "kitchen ALL=(ALL) NOPASSWD:… 3.97kB
5fb86ccb0833 5 minutes ago /bin/sh -c if ! getent passwd kitchen; then … 296kB
113b6affb75e 5 minutes ago /bin/sh -c ssh-keygen -t dsa -f /etc/ssh/ssh… 1.27kB
a87096f2f61d 5 minutes ago /bin/sh -c ssh-keygen -t rsa -f /etc/ssh/ssh… 2.07kB
8bda0cd3ce2e 5 minutes ago /bin/sh -c yum install -y sudo openssh-serve… 109MB
dc1a8eb0af0d 5 minutes ago /bin/sh -c yum clean all 20MB
81f2ddcf99c6 5 minutes ago /bin/sh -c #(nop) ENV container=docker 0B
41f13a9d177b 5 minutes ago /bin/sh -c #(nop) ENV NO_PROXY=10.,.int.kn 0B
de177e2ee788 5 minutes ago /bin/sh -c #(nop) ENV no_proxy=10.,.int.kn 0B
34e56626ac71 5 minutes ago /bin/sh -c #(nop) ENV HTTPS_PROXY=http://zs… 0B
813f933df96b 5 minutes ago /bin/sh -c #(nop) ENV https_proxy=http://zs… 0B
65bd1b2d35ae 5 minutes ago /bin/sh -c #(nop) ENV HTTP_PROXY=http://zsc… 0B
670212484412 5 minutes ago /bin/sh -c #(nop) ENV http_proxy=http://zsc… 0B
e934aafc2206 2 days ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0B
2 days ago /bin/sh -c #(nop) LABEL org.label-schema.sc… 0B
2 days ago /bin/sh -c #(nop) ADD file:f755805244a649ecc… 199MB

Notice:
8bda0cd3ce2e 5 minutes ago /bin/sh -c yum install -y sudo openssh-serve… 109MB

And now run with yum cleanup command added:
IMAGE CREATED CREATED BY SIZE COMMENT
11ec235dda61 5 minutes ago /bin/sh -c echo ssh-rsa\ AAAAB3NzaC1yc2EAAAA… 400B
985e8b319e00 5 minutes ago /bin/sh -c yum -y install net-tools iproute … 27.3MB
ceda4f7b03c2 5 minutes ago /bin/sh -c chmod 0600 /home/kitchen/.ssh/aut… 0B
2d63fe7ab0e6 5 minutes ago /bin/sh -c chown kitchen /home/kitchen/.ssh/… 0B
4cb8d0131c8b 5 minutes ago /bin/sh -c touch /home/kitchen/.ssh/authoriz… 0B
324f1ea6b999 5 minutes ago /bin/sh -c chmod 0700 /home/kitchen/.ssh 0B
9980d4510c48 5 minutes ago /bin/sh -c chown -R kitchen /home/kitchen/.s… 0B
333a80b25231 5 minutes ago /bin/sh -c mkdir -p /home/kitchen/.ssh 0B
9c2e827abce5 5 minutes ago /bin/sh -c echo "Defaults !requiretty" >> /e… 3.99kB
f9d6f324d152 5 minutes ago /bin/sh -c echo "kitchen ALL=(ALL) NOPASSWD:… 3.97kB
89b2e32c633a 5 minutes ago /bin/sh -c if ! getent passwd kitchen; then … 296kB
1e2967d3d39a 5 minutes ago /bin/sh -c ssh-keygen -t dsa -f /etc/ssh/ssh… 1.27kB
6c5ac65c1085 5 minutes ago /bin/sh -c ssh-keygen -t rsa -f /etc/ssh/ssh… 2.07kB
b9ef9d8268ac 5 minutes ago /bin/sh -c yum install -y sudo openssh-serve… 26.7MB
a7b08ac5fd74 6 minutes ago /bin/sh -c yum clean all 20MB
a2a38e12d4cc 6 minutes ago /bin/sh -c #(nop) ENV container=docker 0B
04ee3bc15718 6 minutes ago /bin/sh -c #(nop) ENV NO_PROXY=10.,.int.kn 0B
ab01426f677e 6 minutes ago /bin/sh -c #(nop) ENV no_proxy=10.,.int.kn 0B
df32795d1fc0 6 minutes ago /bin/sh -c #(nop) ENV HTTPS_PROXY=http://zs… 0B
c64b769e5b39 6 minutes ago /bin/sh -c #(nop) ENV https_proxy=http://zs… 0B
efb346c05479 6 minutes ago /bin/sh -c #(nop) ENV HTTP_PROXY=http://zsc… 0B
1f3b74931e63 6 minutes ago /bin/sh -c #(nop) ENV http_proxy=http://zsc… 0B
e934aafc2206 2 days ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0B
2 days ago /bin/sh -c #(nop) LABEL org.label-schema.sc… 0B
2 days ago /bin/sh -c #(nop) ADD file:f755805244a649ecc… 199MB

Notice:
b9ef9d8268ac 5 minutes ago /bin/sh -c yum install -y sudo openssh-serve… 26.7MB