Container Infrastructure Management Service for OpenStack
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container-networking-model.rst 19KB

Magnum Container Networking Model

Launchpad Blueprint:

https://blueprints.launchpad.net/magnum/+spec/extensible-network-model

For Magnum to prosper, the project must support a range of networking tools and techniques, while maintaining a simple, developer-focused user experience. The first step in achieving this goal is to standardize the process of allocating networking to containers, while providing an abstraction for supporting various networking capabilities through pluggable back-end implementations. This document recommends using Docker's libnetwork library to implement container networking abstractions and plugins. Since libnetwork is not a standard and the container ecosystem is rapidly evolving, the Magnum community should continue evaluating container networking options on a frequent basis.

Problem Description

The container networking ecosystem is undergoing rapid changes. The networking tools and techniques used in today's container deployments are different than twelve months ago and will continue to evolve. For example, Flannel1, Kubernetes preferred networking implementation, was initially released in July of 2014 and was not considered preferred until early 2015.

Furthermore, the various container orchestration engines have not standardized on a container networking implementation and may never. For example, Flannel is the preferred container networking implementation for Kubernetes but not for Docker Swarm. Each container networking implementation comes with its own API abstractions, data model, tooling, etc.. Natively supporting each container networking implementation can be a burden on the Magnum community and codebase. By supporting only a subset of container networking implementations, the project may not be widely adopted or may provide a suboptimal user experience.

Lastly, Magnum has limited support for advanced container networking functionality. Magnum instantiates container networks behind the scenes through Heat templates, exposing little-to-no user configurability. Some users require the ability to customize their container environments, including networking details. However, networking needs to "just work" for users that require no networking customizations.

Roles

The following are roles that the Magnum Container Networking Model takes into consideration. Roles are an important reference point when creating user stories. This is because each role provides different functions and has different requirements.

  1. Cloud Provider (CP): Provides standard OpenStack cloud infrastructure services, including the Magnum service.
  2. Container Service Provider (CSP): Uses Magnum to deliver Containers-as-a-Service (CaaS) to users. CSPs are a consumer of CP services and a CaaS provider to users.
  3. Users: Consume Magnum services to provision and manage clustered container environments and deploy apps within the container clusters.

The container ecosystem focuses on the developer user type. It is imperative that the Magnum Container Networking Model meets the need of this user type.

These roles are not mutually exclusive. For example:

  1. A CP can also be a CSP. In this case, the CP/CSP provisions and manages standard OpenStack services, the Magnum service, and provides CaaS services to users.
  2. A User can also be a CSP. In this case, the user provisions their own baymodels, bays, etc. from the CP.

Definitions

COE

Container Orchestration Engine

Baymodel

An object that stores template information about the bay which is used to create new bays consistently.

Bay

A Magnum resource that includes at least one host to run containers on, and a COE to manage containers created on hosts within the bay.

Pod

Is the smallest deployable unit that can be created, scheduled, and managed within Kubernetes.

Additional Magnum definitions can be found in the Magnum Developer documentation2.

Use Cases

This document does not intend to address each use case. The use cases are provided as reference for the long-term development of the Magnum Container Networking Model.

As a User:

  1. I need to easily deploy containerized apps in an OpenStack cloud. My user experience should be similar to how I deploy containerized apps outside of an OpenStack cloud.
  2. I need to have containers communicate with vm-based apps that use OpenStack networking.
  3. I need the option to preserve the container's IP address so I can manage containers by IP's, not just ports.
  4. I need to block unwanted traffic to/from my containerized apps.
  5. I need the ability for my containerized apps to be highly available.
  6. I need confidence that my traffic is secure from other tenants traffic.

As a CSP:

  1. I need to easily deploy a bay for consumption by users. The bay must support the following:
    1. One or more hosts to run containers.
    2. The ability to choose between virtual or physical hosts to run containers.
    3. The ability to automatically provision networking to containers.
  2. I need to provide clustering options that support different container/image, formats and technologies.
  3. After deploying my initial cluster, I need the ability to provide ongoing management, including:
    1. The ability to add/change/remove networks that containers connect to.
    2. The ability to add/change/remove nodes within the cluster.
  4. I need to deploy a Bay without admin rights to OpenStack services.
  5. I need the freedom to choose different container networking tools and techniques offered by the container ecosystem beyond OpenStack.

As a CP:

  1. I need to easily and reliably add the Magnum service to my existing OpenStack cloud environment.
  2. I need to easily manage (monitor, troubleshoot, etc..) the Magnum service. Including the ability to mirror ports to capture traffic for analysis.
  3. I need to make the Magnum services highly-available.
  4. I need to make Magnum services highly performant.
  5. I need to easily scale-out Magnum services as needed.
  6. I need Magnum to be robust regardless of failures within the container orchestration engine.

Proposed Changes

  1. Currently, Magnum supports Flannel3 as the only multi-host container networking implementation. Although Flannel has become widely accepted for providing networking capabilities to Kubernetes-based container clusters, other networking tools exist and future tools may develop.

    This document proposes extending Magnum to support specifying a container networking implementation through a combination of user-facing baymodel configuration flags. Configuration parameters that are common across Magnum or all networking implementations will be exposed as unique flags. For example, a flag named network-driver can be used to instruct Magnum which network driver to use for implementing a baymodel container/pod network. network driver examples may include:

    flannel, weave, calico, midonet, netplugin, etc..

    Here is an example of creating a baymodel that uses Flannel as the network driver: :

    magnum baymodel-create --name k8sbaymodel \
                           --image-id fedora-21-atomic-5 \
                           --keypair-id testkey \
                           --external-network-id 1hsdhs88sddds889 \
                           --dns-nameserver 8.8.8.8 \
                           --flavor-id m1.small \
                           --docker-volume-size 5 \
                           --coe kubernetes \
                           --network-driver flannel

    If no network-driver parameter is supplied by the user, the baymodel is created using the default network driver of the specified Magnum COE. Each COE must support a default network driver and each driver must provide reasonable default configurations that allow users to instantiate a COE without supplying labels. The default network driver for each COE should be consistent with existing Magnum default settings. Where current defaults do not exist, the defaults should be consistent with upstream network driver projects.

  2. Each network driver supports a range of configuration parameters that should be observed by Magnum. This document suggests using an attribute named "labels" for supplying driver-specific configuration parameters. Labels consist of one or more arbitrary key/value pairs. Here is an example of using labels to change default settings of the Flannel network driver: :

    magnum baymodel-create --name k8sbaymodel \
                           --image-id fedora-21-atomic-5 \
                           --keypair-id testkey \
                           --external-network-id ${NIC_ID} \
                           --dns-nameserver 8.8.8.8 \
                           --flavor-id m1.small \
                           --docker-volume-size 5 \
                           --coe kubernetes \
                           --network-driver flannel \
                           --labels flannel_network_cidr=10.0.0.0/8,\
                                    flannel_network_subnetlen=22,\
                                    flannel_backend=vxlan

    With Magnum's current implementation, this document would support labels for the Kubernetes COE type. However, labels are applicable beyond Kubernetes, as the Docker daemon, images and containers now support labels as a mechanism for providing custom metadata. The labels attribute within Magnum should be extended beyond Kubernetes pods, so a single mechanism can be used to pass arbitrary metadata throughout the entire system. A blueprint4 has been registered to expand the scope of labels for Magnum. This document intends on adhering to the expand-labels-scope blueprint.

    Note: Support for daemon-labels was added in Docker 1.4.1. Labels for containers and images were introduced in Docker 1.6.0

    If the --network-driver flag is specified without any labels, default configuration values of the driver will be used by the baymodel. These defaults are set within the Heat template of the associated COE. Magnum should ignore label keys and/or values not understood by any of the templates during the baymodel operation.

    Magnum will continue to CRUD bays in the same way:

    magnum bay-create --name k8sbay --baymodel k8sbaymodel --node-count 1

  3. Update python-magnumclient to understand the new Container Networking Model attributes. The client should also be updated to support passing the --labels flag according to the expand-labels-scope blueprint5.
  4. Update the conductor template definitions to support the new Container Networking Model attributes.
  5. Refactor Heat templates to support the Magnum Container Networking Model. Currently, Heat templates embed Flannel-specific configuration within top-level templates. For example, the top-level Kubernetes Heat template6 contains the flannel_network_subnetlen parameter. Network driver specific configurations should be removed from all top-level templates and instead be implemented in one or more template fragments. As it relates to container networking, top-level templates should only expose the labels and generalized parameters such as network-driver. Heat templates, template definitions and definition entry points should be suited for composition, allowing for a range of supported labels. This document intends to follow the refactor-heat-templates blueprint7 to achieve this goal.
  6. Update unit and functional tests to support the new attributes of the Magnum Container Networking Model.
  7. The spec will not add support for natively managing container networks. Due to each network driver supporting different API operations, this document suggests that Magnum not natively manage container networks at this time and instead leave this job to native tools. References89 1011. provide additional details to common labels operations.
  8. Since implementing the expand-labels-scope blueprint12 may take a while, exposing network functionality through baymodel configuration parameters should be considered as an interim solution.

Alternatives

  1. Observe all networking configuration parameters, including labels within a configuration file instead of exposing the labels attribute to the user.
  2. Only support a single networking implementation such as Flannel. Flannel is currently supported for the Kubernetes COE type. It can be ported to support the swarm COE type.
  3. Add support for managing container networks. This will require adding abstractions for each supported network driver or creating an abstraction layer that covers all possible network drivers.
  4. Use the Kuryr project13 to provide networking to Magnum containers. Kuryr currently contains no documentation or code, so this alternative is highly unlikely if the Magnum community requires a pluggable container networking implementation in the near future. However, Kuryr could become the long-term solution for container networking within OpenStack. A decision should be made by the Magnum community whether to move forward with Magnum's own container networking model or to wait for Kuryr to mature. In the meantime, this document suggests the Magnum community become involved in the Kuryr project.

Data Model Impact

This document adds the labels and network-driver attribute to the baymodel database table. A migration script will be provided to support the attribute being added. :

+-------------------+-----------------+---------------------------------------------+
|    Attribute      |     Type        |             Description                     |
+===================+=================+=============================================+
|     labels        | JSONEncodedDict | One or more arbitrary key/value pairs       |
+-------------------+-----------------+---------------------------------------------+
|    network-driver |    string       | Container networking backend implementation |
+-------------------+-----------------+---------------------------------------------+

REST API Impact

This document adds the labels and network-driver attribute to the BayModel API class. :

+-------------------+-----------------+---------------------------------------------+
|    Attribute      |     Type        |             Description                     |
+===================+=================+=============================================+
|     labels        | JSONEncodedDict | One or more arbitrary key/value pairs       |
+-------------------+-----------------+---------------------------------------------+
|    network-driver |    string       | Container networking backend implementation |
+-------------------+-----------------+---------------------------------------------+

Security Impact

Supporting more than one network driver increases the attack footprint of Magnum.

Notifications Impact

None

Other End User Impact

Most end users will never use the labels configuration flag and simply use the default network driver and associated configuration options. For those that wish to customize their container networking environment, it will be important to understand what network-driver and labels are supported, along with their associated configuration options, capabilities, etc..

Performance Impact

Performance will depend upon the chosen network driver and its associated configuration. For example, when creating a baymodel with "--network-driver flannel" flag, Flannel's default configuration will be used. If the default for Flannel is an overlay networking technique (i.e. VXLAN), then networking performance will be less than if Flannel used the host-gw configuration that does not perform additional packet encapsulation to/from containers. If additional performance is required when using this driver, Flannel's host-gw configuration option could be exposed by the associated Heat template and instantiated through the labels attribute.

Other Deployer Impact

Currently, container networking and OpenStack networking are different entities. Since no integration exists between the two, deployers/operators will be required to manage each networking environment individually. However, Magnum users will continue to deploy baymodels, bays, containers, etc. without having to specify any networking parameters. This will be accomplished by setting reasonable default parameters within the Heat templates.

Developer impact

None

Implementation

Assignee(s)

Primary assignee: Daneyon Hansen (danehans)

Other contributors: Ton Ngo (Tango) Hongbin Lu (hongbin)

Work Items

  1. Extend the Magnum API to support new baymodel attributes.
  2. Extend the Client API to support new baymodel attributes.
  3. Extend baymodel objects to support new baymodel attributes. Provide a database migration script for adding attributes.
  4. Refactor Heat templates to support the Magnum Container Networking Model.
  5. Update Conductor template definitions and definition entry points to support Heat template refactoring.
  6. Extend unit and functional tests to support new baymodel attributes.

Dependencies

Although adding support for these new attributes does not depend on the following blueprints, it's highly recommended that the Magnum Container Networking Model be developed in concert with the blueprints to maintain development continuity within the project.

  1. Common Plugin Framework Blueprint14.
  2. Expand the Scope of Labels Blueprint15.
  3. Refactor Heat Templates, Definitions and Entry Points Blueprint16.

Testing

Each commit will be accompanied with unit tests. There will also be functional tests which will be used as part of a cross-functional gate test for Magnum.

Documentation Impact

The Magnum Developer Quickstart document will be updated to support the configuration flags introduced by this document. Additionally, background information on how to use these flags will be included.

References


  1. https://github.com/coreos/flannel

  2. http://docs.openstack.org/developer/magnum/

  3. https://github.com/coreos/flannel

  4. http://docs.openstack.org/developer/magnum/

  5. http://docs.openstack.org/developer/magnum/

  6. https://github.com/openstack/magnum/blob/master/magnum/templates/kubernetes/kubecluster.yaml

  7. https://blueprints.launchpad.net/magnum/+spec/refactor-heat-templates

  8. https://github.com/docker/libnetwork/blob/master/docs/design.md

  9. https://github.com/GoogleCloudPlatform/kubernetes/blob/master/docs/design/networking.md

  10. https://github.com/coreos/flannel

  11. https://github.com/coreos/rkt/blob/master/Documentation/networking.md

  12. http://docs.openstack.org/developer/magnum/

  13. https://github.com/openstack/kuryr

  14. https://blueprints.launchpad.net/magnum/+spec/common-plugin-framework

  15. https://blueprints.launchpad.net/magnum/+spec/expand-labels-scope

  16. https://blueprints.launchpad.net/magnum/+spec/refactor-heat-templates