[Base] Terminology for docker/atomic images

[Adam Young]

On 09/08/2014 10:17 AM, Dusty Mabe wrote:
> On Mon, Sep 08, 2014 at 09:28:20AM -0400, Adam Young wrote:
>> On 09/07/2014 11:22 PM, Dusty Mabe wrote:
>>> Hi All,
>>>
>>> Per discussion in the #fedora-cloud meeting last Friday I would like to
>>> start a thread about the names of the Docker and Atomic deliverables for F21.
>>>
>>> I know of at least a few cases where there has been confusion regarding
>>> what deliverable has been the subject of a conversation on IRC as a result
>>> of the current terminology. I've seen the docker and atomic referred to as:
>>>
>>>      Docker Image
>>>      Atomic Image
>>>      Docker Host Image
>>>      etc...
>>>
>>> It seems like the one that sparks the most confusion is "Docker Image".
>>> Usually when I see "Image" I think a VM bootable image (i.e. virtualization,
>>> not containers/Docker). A progression from that misunderstanding could lead
>>> one to think that "Docker Image" is the VM disk image I can use to boot a
>>> host that will run the Docker daemon and thus run containers.
>>>
>>> I think it would be nice to help ourselves and our users along by separating
>>> the terminology a bit such that it is hard to confuse what is a VM disk
>>> image vs. what is an image for use with Docker.
>>>
>>> Here is a first stab at trying to make things clearer:
>>>
>>>
>>>      Docker Container Image - base container image - can be used with docker
>>>      Atomic Image           - minimal OS, Atomic updates, aka 'Docker Host'
>> I've always thought container and image were two distinct things.
> Image and container are two distinct things. The container image is basically an
> image that contains a filesystem for use with containers (no kernel, etc..).
Yeah.  I hate this use of container.  The Kernel is irrelevant.

In both the Container and VM worlds there is the specification for what 
the container/machine should look like when it is activated. But these 
are not the container.

Its like calling a Zip file or RPM a container because it contains the 
files that will become the VM...strictly speaking correct, but IMHO 
meaningless.

>
> A container is an isolated process that runs that uses the container image as
> the root filesystem.


I'd prefer "A container is an isolated process that runs that uses the  
image as the root filesystem."

(even then I would prefer that "image" be slightly more specified to 
distinguish it from a picture;  to the rest of the world, an image is a 
jpg/gif/png/bmp,  not a Filesystem snapshot.  But them, I am unbearable 
pedantic.)


>
>>
>> Here's my take:
>>
>>
>> The image is the disk that is being used.  The container is the
>> Operating System construct.  The  Two combinded are the instance.
>>
>> "My instance is a Fedora 21 base image running inside a KVM container."
>>
>> "My instance is a Docker image of JBoss with RHQ in it running in a
>> container on CentOS 7"
> I think you are mixing virtualization and containerization too much. Let me try
> to see if I can use similar statements in my own terms:
Lets not try to separate the verbage of these two things. Containers are 
degenerate cases.  Put another way, Virtual machines are extreme 
containers....or something.  The same abstractions apply to each, with 
additional layers necessary for Virtual Machines.  For the sake of poor 
sysadmins everywhere, lets try to give them sane, simple language that 
covers both.
>
> "My virtual machine instance is a Fedora 21 base image running on a KVM hypervisor"
>
> "My container is running process X that is using a docker container image of JBoss
>   with RHQ in it. The Docker daemon managing my container is running on a CentOS 7 host."

See, I find that second one both too verbose and too confusing without 
conveying any more accurate information.

"I'm running JBoss from a docker image in a container on CentOS 7" is 
just as clear and accurate.

Thanks for starting this discussion, BTW.  I think the verbage around 
this has confused many people for a while.


>
> Hopefully my take on this isn't wrong. Does this help at all?
>
> Dusty
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