zun/specs/container-snapshot.rst

Container Snapshot

Related Launchpad Blueprint:

https://blueprints.launchpad.net/zun/+spec/container-snapshot Zun needs to snapshot a running container, and make it available to user. Potentially, a user can restore the container from this snapshot image.

Problem description

It is a common requirement from users of containers to save the changes of a current running container to a new image. Zun currently does not support taking a snapshot of a container.

Proposed change

1. Introduce a new CLI command to enable a user to take a snapshot of a running container instance:

   $ zun commit <container-name> <image-name>
   
   $ zun help commit
   
   usage: zun commit <container-name> <image-name>
           Create a new image by taking a snapshot of a running container.
   Positional arguments:
           <container-name>              Name or ID of container.
           <image-name>                  Name of snapshot.

2. Extend docker driver to enable "docker commit" command to create a new image.

3. The new image should be accessible from other hosts. There are two options to support this:

   1. upload the image to glance

   b) upload the image to docker hub Option a) will be implemented as default; future enhancement can be done to support option b).

Design Principles

Similar user experience between VMs and containers. In particular, the ways to snapshot a container should be similar as the VM equivalent.

Alternatives

1. Using linked volumes to persistent changes in a container.
2. Use docker cp to copy data from the container onto the host machine.

Data model impact

None

REST API impact

Creates an image from a container.

Specify the image name in the request body.

After making this request, a user typically must keep polling the status of the created image from glance to determine whether the request succeeded. If the operation succeeds, the created image has a status of active. User can also see the new image in the image back end that OpenStack Image service manages.

Preconditions:

1. The container must exist.
2. User can only create a new image from the container when its status is Running, Stopped, and Paused.
3. The connection to the Image service is valid.

POST /containers/<ID>/commit:        commit a container
Example commit
{
    "image-name" : "foo-image"
}

Response: If successful, this method does not return content in the response body. - Normal response codes: 202 - Error response codes: BadRequest(400), Unauthorized(401), Forbidden(403), ItemNotFound(404)

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

None

Developer impact

None

Implementation

Assignee(s) Primary assignee: Bin Zhou Other contributors: Work Items 1. Expend docker driver to enable "docker commit". 2. Upload the generated image to glance. 3. Implement a new API endpoint for createImage. 4. Implement unit/integration test.

Dependencies

None

Testing

Each patch will have unit tests, and Tempest functional tests covered.

Documentation Impact

A set of documentation for this new feature will be required.