Here is a bit more context.

Currently, at k8s and swarm bay, some required binaries (i.e. etcd and flannel) 
are built into image and run at host. We are exploring the possibility to 
containerize some of these system components. The rationales are (i) it is 
infeasible to build custom packages into an atomic image and (ii) it is 
infeasible to upgrade individual component. For example, if there is a bug in 
current version of flannel and we know the bug was fixed in the next version, 
we need to upgrade flannel by building a new image, which is a tedious process.

To containerize flannel, we need a second docker daemon, called 
docker-bootstrap [1]. In this setup, pods are running on the main docker 
daemon, and flannel and etcd are running on the second docker daemon. The 
reason is that flannel needs to manage the network of the main docker daemon, 
so it needs to run on a separated daemon.

Daneyon, I think it requires separated storage because it needs to run a 
separated docker daemon (unless there is a way to make two docker daemons share 
the same storage).

Wanghua, is it possible to leverage Cinder volume for that. Leveraging external 
storage is always preferred [2].


Best regards,

From: Daneyon Hansen (danehans) []
Sent: November-25-15 11:10 AM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [magnum]storage for docker-bootstrap

From: 王华 <<>>
Reply-To: "OpenStack Development Mailing List (not for usage questions)" 
Date: Wednesday, November 25, 2015 at 5:00 AM
To: "OpenStack Development Mailing List (not for usage questions)" 
Subject: [openstack-dev] [magnum]storage for docker-bootstrap

Hi all,

I am working on containerizing etcd and flannel. But I met a problem. As 
described in [1], we need a docker-bootstrap. Docker and docker-bootstrap can 
not use the same storage, so we need some disk space for it.

I reviewed [1] and I do not see where the bootstrap docker instance requires 
separate storage.

The docker in master node stores data in /dev/mapper/atomicos-docker--data and 
metadata in /dev/mapper/atomicos-docker--meta. The disk space left is too same 
for docker-bootstrap. Even if the root_gb of the instance flavor is 20G, only 
8G can be used in our image. I want to make it bigger. One way is we can add 
the disk space left in the vda as vda3 into atomicos vg after the instance 
starts and we allocate two logic volumes for docker-bootstrap. Another way is 
when we create the image, we allocate two logic volumes for docker-bootstrap. 
The second way has a advantage. It doesn't have to make filesystem when the 
instance is created which is time consuming.

What is your opinion?

Best Regards

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