Comment 3 for bug 1735076

Reviewed: https://review.openstack.org/571991
Committed: https://git.openstack.org/cgit/openstack/zun/commit/?id=48075909a9a66b35e45896eeaac65d8597648e3a
Submitter: Zuul
Branch: master

commit 48075909a9a66b35e45896eeaac65d8597648e3a
Author: Hongbin Lu <email address hidden>
Date: Sun Jun 3 21:52:13 2018 +0000

    Add exec_instances to data model

    Zun is going to implement a proxy for interactive execute.
    The first step is to introduce data model for tracking each
    exec instances of a container. An exec instance in Zun is
    an one-to-one mapping for exec instance in Docker.
    We will use it to track a docker's exec instance as well as
    a generated token for granting access of this exec instance.
    In the future, the websocket proxy will retrieve the token from
    incoming request and match it to the one stored in DB.
    The request will be rejected if the token doesn't match.

    This patch introduces the data model of exec_instance
    in DB api and objects layer. It basically contains three
    fields: container_id, exec_id, url, token.
    The container_id is the id of the container record in Zun.
    The exec_id is the ID of the docker's exec instance.
    The url is the docker daemon endpoint for the exec instance
    The token is as described above.

    Partial-Bug: #1735076
    Change-Id: Ib38a46c0e3f3aae58e1f562536b858bc4cd23bf8