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title authors owning-sig participating-sigs reviewers approvers editor creation-date last-updated status
Removing In-Tree Cloud Providers
@andrewsykim
@cheftako
sig-cloudprovider
sig-apps
sig-aws
sig-azure
sig-apimachinery
sig-gcp
sig-network
sig-openstack
sig-storage
@andrewsykim
@cheftako
@d-nishi
@dims
@hogepodge
@mcrute
@steward-yu
@thockin
@liggit
TBD
2018-12-18
2019-04-11
implementable

Removing In-Tree Cloud Provider Code

Table of Contents

Terms

  • CCM: Cloud Controller Manager - The controller manager responsible for running cloud provider dependent logic, such as the service and route controllers.
  • KCM: Kubernetes Controller Manager - The controller manager responsible for running generic Kubernetes logic, such as job and node_lifecycle controllers.
  • KAS: Kubernetes API Server - The core api server responsible for handling all API requests for the Kubernetes control plane. This includes things like namespace, node, pod and job resources.
  • K8s/K8s: The core kubernetes github repository.
  • K8s/cloud-provider: Any or all of the repos for each cloud provider. Examples include cloud-provider-gcp, cloud-provider-aws and cloud-provider-azure. We have created these repos for each of the in-tree cloud providers. This document assumes in various places that the cloud providers will place the relevant code in these repos. Whether this is a long-term solution to which additional cloud providers will be added, or an incremental step toward moving out of the Kubernetes org is out of scope of this document, and merits discussion in a broader forum and input from SIG-Architecture and Steering Committee.
  • K8s SIGs/library: Any SIG owned repository.
  • Staging: Staging: Separate repositories which are currently visible under the K8s/K8s repo, which contain code considered to be safe to be vendored outside of the K8s/K8s repo and which should eventually be fully separated from the K8s/K8s repo. Contents of Staging are prevented from depending on code in K8s/K8s which are not in Staging. Controlled by publishing kubernetes-rules-configmap
  • In-tree: code that lives in the core Kubernetes repository k8s.io/kubernetes.
  • Out-of-Tree: code that lives in an external repository outside of k8s.io/kubernetes.

Summary

This is a proposal outlining steps to remove "in-tree" cloud provider code from the k8s.io/kubernetes repo while being as least disruptive to end users and other Kubernetes developers as possible.

Motivation

Motiviation behind this effort is to allow cloud providers to develop and make releases independent from the core Kubernetes release cycle. The de-coupling of cloud provider code allows for separation of concern between "Kubernetes core" and the cloud providers within the ecosystem. In addition, this ensures all cloud providers in the ecosystem are integrating with Kubernetes in a consistent and extendable way.

Having all cloud providers developed/released in their own external repos/modules will result in the following benefits:

  • The core pieces of Kubernetes (kubelet, kube-apiserver, kube-controller-manager, etc) will no longer depend on cloud provider specific APIs (and their dependencies). This results in smaller binaries and lowers the chance of security vulnerabilities via external dependencies.
  • Each cloud provider is free to release features/bug fixes at their own schedule rather than relying on the core Kubernetes release cycle.

Goals

  • Remove all cloud provider specific code from the k8s.io/kubernetes repository with minimal disruption to end users and developers.

Non-Goals

  • Testing/validating out-of-tree provider code for all cloud providers, this should be done by each provider.

Proposal

Approach

In order to remove cloud provider code from k8s.io/kubernetes. A 3 phase approach will be taken.

  1. Move all code in k8s.io/kubernetes/pkg/cloudprovider/providers/<provider> to k8s.io/kubernetes/staging/src/k8s.io/legacy-cloud-providers/<provider>/. This requires removing all internal dependencies in each cloud provider to k8s.io/kubernetes.
  2. Begin to build/release the CCM from external repos (k8s.io/cloud-provider-<provider>) with the option to import the legacy providers from k8s.io/legacy-cloud-providers/<provider>. This allows the cloud-controller-manager to opt into legacy behavior in-tree (for compatibility reasons) or build new implementations of the provider. Development for cloud providers in-tree is still done in k8s.io/kubernetes/staging/src/k8s.io/legacy-cloud-providers/<provider> during this phase.
  3. Delete all code in k8s.io/kubernetes/staging/src/k8s.io/legacy-cloud-providers and shift main development to k8s.io/cloud-provider-<provider>. External cloud provider repos can optionally still import k8s.io/legacy-cloud-providers but it will no longer be imported from core components in k8s.io/kubernetes.

Phase 1 - Moving Cloud Provider Code to Staging

In Phase 1, all cloud provider code in k8s.io/kubernetes/pkg/cloudprovider/providers/<provider> will be moved to k8s.io/kubernetes/staging/src/k8s.io/legacy-cloud-providers/<provider>. Reasons why we "stage" cloud providers as the first phase are:

  • The staged legacy provider repos can be imported from the out-of-tree provider if they choose to opt into the in-tree cloud provider implementation. This allows for a smoother transition between in-tree and out-of-tree providers in cases where there are version incompatibilites between the two.
  • Staging the cloud providers indicates to the community that they are slated for removal in the future.

The biggest challenge of this phase is to remove dependences to k8s.io/kubernetes in all the providers. This is a requirement of staging a repository and a best practice for consuming external dependencies. All other repos "staged" (client-go, apimachinery, api, etc) in Kubernetes follow the same pattern. The full list of internal dependencies that need to be removed can be found in issue 69585.

Phase 2 - Building CCM from Provider Repos

In Phase 2, cloud providers will be expected to build the cloud controller manager from their respective provider repos (k8s.io/cloud-provider-<provider>). Providers can choose to vendor in their legacy provider in k8s.io/legacy-cloud-providers/<provider>, build implementations from scratch or both. Development in-tree is still done in the staging directories under the k8s.io/kubernetes repo.

The kube-controller-manager will still import the cloud provider implementations in staging. The package location of the provider implementations will change because each staged directory will be "vendored" in from their respective staging directory. The only change in core components is how the cloud providers are imported and the behavior of each cloud provider should not change.

Phase 3 - Migrating Provider Code to Provider Repos

In Phase 3, all code in k8s.io/kubernetes/staging/src/k8s.io/legacy-cloud-providers/<provider> will be removed and development of each cloud provider should be done in their respective external repos. It's important that by this phase, both in-tree and out-of-tree cloud providers are tested and production ready. Ideally most Kubernetes clusters in production should be using the out-of-tree provider before in-tree support is removed. A plan to migrate existing clusters from using the kube-controller-manager to the cloud-controller-manager is currently being developed. More details soon.

External cloud providers can optionally still import providers from k8s.io/legacy-cloud-providers but no core components in k8s.io/kubernetes will import the legacy provider and the respective staging directory will be removed along with all its dependencies.

Staging Directory

There are several sections of code which need to be shared between the K8s/K8s repo and the K8s/Cloud-provider repos. The plan for doing that sharing is to move the relevant code into the Staging directory as that is where we share code today. The current Staging repo has the following packages in it.

  • Api
  • Apiextensions-apiserver
  • Apimachinery
  • Apiserver
  • Client-go
  • Code-generator
  • Kube-aggregator
  • Metrics
  • Sample-apiserver
  • Sample-Controller

With the additions needed in the short term to make this work; the Staging area would now need to look as follows.

  • Api
  • Apiextensions-apiserver
  • Apimachinery
  • Apiserver
  • Client-go
  • legacy-cloud-providers
  • Code-generator
  • Kube-aggregator
  • Metrics
  • Sample-apiserver
  • Sample-Controller

Cloud Provider Instances

Currently in K8s/K8s the cloud providers are actually included in the providers.go file which then includes each of the in-tree cloud providers. In the short term, we would leave that file where it is and adjust it to point at the new homes under Staging. For the K8s/cloud-provider repo, would have the following CCM wrapper file. (Essentially a modified copy of cmd/cloud-controller-manager/controller-manager.go) The wrapper for each cloud provider would import just their vendored cloud-provider implementation rather than providers.go file.

k8s/k8s: pkg/cloudprovider/providers/providers.go


import (
  // Prior to cloud providers having been moved to Staging
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/aws"
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/azure"
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/cloudstack"
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/gce"
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/openstack"
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/ovirt"
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/photon"
  _ "k8s.io/kubernetes/pkg/cloudprovider/providers/vsphere"
)

k8s/cloud-provider-gcp: pkg/cloudprovider/providers/providers.go


import (
  // Cloud providers
  _ "k8s.io/legacy-cloud-providers/aws"
  _ "k8s.io/legacy-cloud-providers/azure"
  _ "k8s.io/legacy-cloud-providers/gce"
  _ "k8s.io/legacy-cloud-providers/openstack"
  _ "k8s.io/legacy-cloud-providers/vsphere"
)

Alternatives

Staging Alternatives

Git Filter-Branch

One possible alternative is to make use of a Git Filter Branch to extract a sub-directory into a virtual repo. The repo needs to be sync'd in an ongoing basis with K8s/K8s as we want one source of truth until K8s/K8s does not pull in the code. This has issues such as not giving K8s/K8s developers any indications of what the dependencies various K8s/Cloud-providers have. Without that information it becomes very easy to accidentally break various cloud providers and time you change dependencies in the K8s/K8s repo. With staging the dependency line is simple and automatically enforced. Things in Staging are not allowed to depend on things outside of Staging. If you want to add such a dependency you need to add the dependent code to Staging. The act of doing this means that code should get synced and solve the problem. In addition the usage of a second different library and repo movement mechanism will make things more difficult for everyone.

“Trying to share code through the git filter will not provide this protection. In addition it means that we now have two sharing code mechanisms which increases complexity on the community and build tooling. As such I think it is better to continue to use the Staging mechanisms. ”

Build Location Alternatives

Build K8s/K8s from within K8s/Cloud-provider

The idea here is to avoid having to add a new build target to K8s/K8s. The K8s/Cloud-provider could have their own custom targets for building things like KAS without other cloud-providers implementations linked in. It would also allow other customizations of the standard binaries to be created. While a powerful tool, this mechanism seems to encourage customization of these core binaries and as such to be discouraged. Providing the appropriate generic binaries cuts down on the need to duplicate build logic for these core components and allow each optimization of build. Download prebuilt images at a version and then just build the appropriate addons.

Build K8s/Cloud-provider within K8s/K8s

The idea here would be to treat the various K8s/Cloud-provider repos as libraries. You would specify a build flavor and we would pull in the relevant code based on what you specified. This would put tight restrictions on how the K8s/Cloud-provider repos would work as they would need to be consumed by the K8s/K8s build system. This seems less extensible and removes the nice loose coupling which the other systems have. It also makes it difficult for the cloud providers to control their release cadence.

Config Alternatives

Use component config to determine where controllers run

Currently KCM and CCM have their configuration passed in as command line flags. If their configuration were obtained from a configuration server (component config) then we could have a single source of truth about where each controller should be run. This both solves the HA migration issue and other concerns about making sure that a controller only runs in 1 controller manager. Rather than having the controllers as on or off, controllers would now be configured to state where they should run, KCM, CCM, Nowhere, … If the KCM could handle this as a run-time change nothing would need to change. Otherwise it becomes a slight variant of the proposed solution. This is probably the correct long term solution. However for the timeline we are currently working with we should use the proposed solution.

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