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<p>Thanks Devdatta/Maxime for your comments.</p>
<p><br>
</p>
<p><br>
</p>
<p>I am definitely not rigid about implementing the workflow in Nova
and it's well known that there can be multiple integration points
for this work including that in docker itself. However, there are
two prime reasons why we chose Nova as integration point in
OpenStack:<br>
<br>
1. Minimal changes to a VM boot workflow. No need to depend on
Swift or any other service. <br>
2. Faster boot up times - since the downloading of the virtual
machine image is negated. Downloading the docker filesystems
should be more or less easier.</p>
<p><br>
</p>
<p>Some comments inline.</p>
<p><br>
</p>
<p>Thanks,</p>
<p>Sudipto<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 27/07/16 11:59 PM, Maxime Belanger
wrote:<br>
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<p>+1 on this,</p>
<p><br>
</p>
<p>Still you loose all the great stuff about the containers
but it is a first step towards native container
orchestration platform.</p>
</div>
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</blockquote>
IMHO, it is not about just losing stuff. We are not emulating a
docker workflow. The expectation is to have the ability to run a
container inside a virtual machine and then take that filesystem out
and run it natively on the hardware as desired. You can debate on
whether it's really needed in Nova or elsewhere and I think that's a
fair debate. <br>
<br>
I am sure there are further technical challenges to overcome, if we
want to think in this direction.<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font style="font-size:11pt"
face="Calibri, sans-serif" color="#000000"><b>From:</b>
Devdatta Kulkarni <a class="moz-txt-link-rfc2396E" href="mailto:devdatta.kulkarni@RACKSPACE.COM"><devdatta.kulkarni@RACKSPACE.COM></a><br>
<b>Sent:</b> July 27, 2016 12:21:30 PM<br>
<b>To:</b> OpenStack Development Mailing List (not for usage
questions)<br>
<b>Subject:</b> Re: [openstack-dev] [nova][rfc] Booting
docker images using nova libvirt</font>
<div> </div>
</div>
</div>
<font size="2"><span style="font-size:10pt;">
<div class="PlainText">Hi Sudipta,<br>
<br>
There is another approach you can consider which does not
need any changes to Nova.<br>
<br>
The approach works as follows:<br>
- Save the container image tar in Swift<br>
- Generate a Swift tempURL for the container file<br>
- Boot Nova vm and pass instructions for following steps
through cloud init / user data<br>
- download the container file from Swift (wget)<br>
</div>
</span></font></blockquote>
<font size="2">I believe this has to be carried out for every docker
image? That is if i have a nginx image and it's provisioned twice,
a fresh copy of such has to be wget'ed every time? IF the nova
workflow is acceptable, then there can be optimizations thought
around this. At this moment, my implementation copies the cached
image for each of the containers - atleast making further boots
faster.<br>
Also, how do you tackle the problem with snapshoting a container?<br>
</font>
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<div class="PlainText">
- load it (docker load)<br>
- run it (docker run)<br>
</div>
</span></font></blockquote>
<font size="2">Do you run the docker native commands inside the
virtual machine? In such a case, do you actually install docker<br>
as a part of the cloud-init scripts? Do you have numbers w.r.t the
boot time of the container image in this case?<br>
</font>
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<div class="PlainText">
We have implemented this approach in Solum (where we use
Heat for deploying a VM and<br>
then run application container on it by providing above
instructions through user_data of the HOT).<br>
<br>
Thanks,<br>
Devdatta<br>
<br>
<br>
-----<br>
<br>
<br>
From: Sudipta Biswas <a class="moz-txt-link-rfc2396E" href="mailto:sbiswas7@linux.vnet.ibm.com"><sbiswas7@linux.vnet.ibm.com></a><br>
Sent: Wednesday, July 27, 2016 9:17 AM<br>
To: OpenStack Development Mailing List (not for usage
questions)<br>
Subject: [openstack-dev] [nova][rfc] Booting docker images
using nova libvirt<br>
<br>
Premise:<br>
<br>
While working with customers, we have realized:<br>
<br>
- They want to use containers but are wary of using the same
host kernel for multiple containers.<br>
- They already have a significant investment (including
skills) in OpenStack's Virtual Machine workflow and would
like to re-use it as much as possible.<br>
- They are very interested in using docker images.<br>
<br>
There are some existing approaches like Hyper, Secure
Containers workflows which already tries to address the
first point. But we wanted to arrive at an approach that
addresses all the above three in context of OpenStack Nova
with minimalist changes.<br>
<br>
<br>
Design Considerations:<br>
<br>
We tried a few experiments with the present libvirt driver
in nova to accomplish a work flow to deploy containers
inside virtual machines in OpenStack via Nova.<br>
<br>
The fundamental premise of our approach is to run a single
container encapsulated in a single VM. This VM image just
has a bare minimum operating system required to run it.<br>
The container filesystem comes from the docker image.<br>
<br>
We would like to get the feedback on the below approaches
from the community before proposing this as a spec or
blueprint.<br>
<br>
<br>
Approach 1<br>
<br>
User workflow:<br>
<br>
1. The docker image is obtained in the form of a tar file.<br>
2. Upload this tar file in glance. This support is already
there in glance were a container-type of docker is
supported.<br>
3. Use this image along with nova libvirt driver to deploy a
virtual machine.<br>
<br>
Following are some of the changes to the OpenStack code that
implements this approach:<br>
<br>
1. Define a new conf parameter in nova called –
base_vm_image=/var/lib/libvirt/images/baseimage.qcow2<br>
This option is used to specify the base VM image.<br>
<br>
2. define a new sub_virt_type = container in nova conf.
Setting this parameter will ensure mounting of the container
filesystem inside the VM.<br>
Unless qemu and kvm are used as virt_type – this workflow
will not work at this moment.<br>
<br>
3. In the virt/libvirt/driver.py we do the following based
on the sub_virt_type = container:<br>
<br>
- We create a qcow2 disk from the base_vm_image and expose
that 'disk' as the boot disk for the virtual machine.<br>
Note – this is very similar to a regular virtual machine
boot minus the fact that the image is not downloaded from<br>
glance but instead it is present on the host.<br>
<br>
<br>
- We download the docker image into the
/var/lib/nova/instances/_base directory and then for each
new virtual machine boot – we create a new directory
/var/lib/nova/instances/<instance_uuid> as it's and
copy the docker filesystem to it. Note – there are
subsequent improvements to this idea that could be performed
around the lines of using a union filesystem approach.<br>
- The step above allows each virtual machine to have a
different copy of the filesystem.<br>
- We create a 'passthrough' mount of the filesystem via
libvirt. This code is also present in the nova libvirt
driver and we just trigger it based on our sub_virt_type
parameter.<br>
<br>
4. A cloud init – userdata is provided that looks somewhat
like this:<br>
<br>
runcmd:<br>
- mount -t 9p -o trans=virtio share_dir /mnt<br>
- chroot /mnt /bin/<command_to_run><br>
<br>
The command_to_run is usually the entrypoint to for the
docker image.<br>
<br>
There could be better approaches to determine the entrypoint
as well (say from docker image metadata).<br>
<br>
<br>
Approach 2.<br>
<br>
In this approach, the workflow remains the same as the first
one with the exception that the<br>
docker image is changed into a qcow2 image using a tool like
virt-make-fs before uploading it to glance, instead of a tar
file.<br>
<br>
A tool like virt-make-fs can convert a tar file to a qcow2
image very easily.<br>
<br>
This image is then downloaded on the compute node and a
qcow2 disk is created/attached to the virtual machine that
boots using the base_vm_image.<br>
<br>
<br>
Approach 3<br>
<br>
A custom qcow2 image is created using kernel, initramfs and
the docker image and uploaded to glance. No changes are
needed in openstack nova. It boots as a regular VM.<br>
<br>
Changes will be needed in image generation tools and will
involve few additional tasks from an operator point of view.<br>
<br>
<br>
I look forward to your comments/suggestions on the above.<br>
<br>
<br>
Thanks,<br>
Sudipto<br>
<br>
<br>
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