Reduce image size produced by machine_image resource

[marc-]

I found that docker image created by machine_image resource has too many redundant layers in it.

REPOSITORY        TAG                 IMAGE ID            VIRTUAL SIZE
chef              test                85d60acf156b        386.7 MB
ubuntu            14.04               2d24f826cb16        188.3 MB

IMAGE         CREATED BY                                                         SIZE
85d60acf156b  chef-client -l auto                                                2 B
d18b21b38ae7  dpkg -i /tmp/chef_12.1.0-1_amd64.deb                               154.4 MB
911920e7729f  /bin/sh -c #(nop) ADD file:<hash> in /tmp/chef_12.1.0-1_amd64.deb  43.96 MB
3f9ff1bb17bb  /bin/sh -c #(nop) ADD file:<hash> in /tmp/detect.sh                3.559 kB
374b13cdedd5  /bin/sh -c #(nop) ADD file:<hash> in /etc/chef/client.rb           132 B
8a3981e5fa44  /bin/sh -c #(nop) ADD file:<hash> in /etc/chef/client.pem          1.679 kB
a6e2feedecb1  mkdir -p /etc/chef+                                                0 B
2d24f826cb16  /bin/sh -c #(nop) CMD [/bin/bash]                                  0 B

Please note 911920e7729f and d18b21b38ae7. Ideally, I believe, it has to be merged into single layer (85d60acf156b). It is also important to allow completely remove chef-client from image to save ~200Mb.

So far the only workaround here is to reimport image with docker export <conainer_id> | sudo docker import - <my_compact_image_name>. Thoug, I personaly don't like this approach because it also wipes out underlying layers of base image (for instance, ubuntu image).

[marc-]

With d06c253 base image size reduced from 411.3 MB to 243.7 MB.
There is still room for improvements, for instance, to install chef-client omnibus on host system instead of container. Though, I'm not sure if packages for different system has same system independent content.