zun/specs/cinder-integration.rst

Container Cinder Integration

Related Launchpad Blueprint:

https://blueprints.launchpad.net/zun/+spec/cinder-zun-integration

Zun needs to manage containers as well as their associated IaaS resources, such as IP addresses, security groups, ports, volumes, etc. Zun containers should be able to use volumes which has multiple storage vendors or plugins support.

As zun is project belongs to OpenStack ecosystem and zun has integration with Cinder which is block storage service.

Fuxi is new OpenStack project which aims to integrate Cinder to docker volumes. With Fuxi, Cinder can be used as the unified persistence storage provider for virtual machine, baremetal and Docker container.

The implementation of Cinder is enabled using fuxi driver from zun. We need to implement Cinder driver in Zun which manages volumes, let Fuxi control the mount/unmount volume from Docker container.

Problem description

To store some large amount data in container is not possible. In case of of containers, all the storage resides in host storage which is not good solution. If host goes down, storage wont be accessible. We need to somehow use cloud storage, which is reliable and we can attach it to container so that people use containers for workloads also.

Proposed change

There are two approaches docker provides to add volume to Container.

1. Using Docker run

docker run -d --volume-driver= Fuxi -v my-named-volume --name web_app

2. Create volume first & then add it to Container

docker volume create --driver fuxi

--name test_vol -o size=1 -o fstype=ext4 -o multiattach=true

docker run -d -v my-named-volume

--name web_app

I think, we can support both

1. To Implement first approach, we need following changes * Introduce fields in Container API - volume-driver, vol-name, vol-size. * We pass call to Volume Driver to create volume. * Volume driver connects to Cinder & handles volume creation. * Once volume is created in Cinder, then we finally go add volume-driver as Fuxi & add volume name which created in cinder. * Fuxi should be installed in Docker host and configured with Cinder engine.

2. To Implement Second approach, we need following changes * Introduce Volume API in Zun which has fields volume-driver, volume-name, volume-size etc. * Volume API will connect to volume driver which will sit under /zun/volume/driver.py. * Volume Driver connects to Cinder and handles volume creation in Cinder. * Once the volume is created in Cinder, it communicates to Docker Volume API to attach the created volume in Docker. * Docker Volume API use --driver=Fuxi which goes talks to Cinder and attach created Volume in Docker. * Prerequisite here is, Fuxi should be installed on docker host & configured with Cinder. If not, it returns the 500 response. * Also we need to introduce new Volume table which contains field vol-driver, vol-name, vol-size fields. * We need to add storage section in conf file, where we can specify some default attributes like storage engine Cinder, Cinder endpoint etc. * We also need to configure Cinder endpoint in Fuxi conf file. * We can use same implementation for Flocker also as it supports Cinder. * I think if we can create separate CinderDriver which calls from Volume volume driver. This approach enables way to implement multiple storages supports in the future and we can plug-in multiple storage implementation.

The diagram below offers an overview of the system architecture. The Zun service may communicate with Fuxi and fuxi talks to Cinder for volumes.

+---------+
|   CLI   |
+----+----+
     |
+----+----+
|+-+ REST +----- Zun ----+|
|+--                   --+|
|+------------+----------+|
     |
|+--------------------+ Volume Driver+-------------+|
||              |                  |                |
||              |                  |                |
||              |                  |                |
||       +-----------+    +---------------+         |
||       | Cinder    |    | Docker Volume |         |
||       +-----------+    +---------------+         |
||                         |            |           |
||                    +---------+    +-----------+  |
||                    |   Fuxi  |    |   Flocker |  |
||                    +----+----+    +-----------+  |
|+------------+ +---------------+ +----------------+|
|                                                   |
+---------------------------------------------------+

Design Principles

1. Similar user experience between VMs and containers. In particular, the ways to configure volumes of a container should be similar as the VM equivalent.
2. Full-featured container APIs.

Alternatives

1. We can use rexray for storage support, its again third party tool which increases the dependency.

Data model impact

Add volume-driver, vol-name, size field in the Volume Table. Need to add volume_id to Container Table.

REST API impact

We need to add below APIs 1. Create a volume - POST /v1/volumes 2. List volumes - GET /v1/volumes 3. Inspect volume - GET /v1/volumes/<uuid> 4. Delect Volume - DELETE /v1/volumes/<uuid>

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

None

Other deployer impact

Deployers need to deploy a Fuxi and Cinder.

Developer impact

None

Implementation

Assignee(s)

Primary assignee: Digambar

Other contributors:

Work Items

1. We need to introduce new Volume API.
2. Implement volume driver in zun.
3. Implement Cinder calls under the volume driver.
4. Implement Docker volume support in Zun.
5. Add volume section in zun.conf.
6. Add volume-driver support in CLI.
7. Implement unit/integration test.

Dependencies

Add a dependency to Cinder.

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.