ed19492dc2
Currently volume and dynamic-resource plugin shares an AssumeCache
implementation. However, they features significantly different use case. DRA
call Assume() on objects returned by APIServer, but volume call Assume() on
objects yet to be sent to the APIServer.
VolumeBinding plugin only makes one update request, while DynamicResource makes
2 requests (add finalizer then update allocation status). Taking advantage of
this, currently the volume cache is simpler:
1. Reserve: assume PV/PVC will be updated
2. PreBind: really send the update request
3. AssumeCache receives an update from informer and overwrite the assumed state.
a. if Prebind succeeded, this will surely include the update from step 2.
b. if PreBind is not finished yet, and this is an irrelevant update, it is safe to
overwrite the assumed state, because our update in PreBind will surely fail with Conflict.
While for DynamicResource:
1. Reserve: add devices to inFlightAllocations
2. PreBind:
a. send the 2 update requests
b. add the returned object into AssumeCache
c. AssumeCache dispatch events synchronously to update allocatedDevices
d. remove devices from inFlightAllocations
DynamicResource needs some features from AssumeCache that is not necessary for VolumeBinding:
1. DynamicResource needs strictly ordered update events to update allocatedDevices,
including those from Assume() and Restore()
2. DynamicResource needs to compare ResourceVersion to prevent the assumed state from being
overwritten by older version from informer. While this works, the doc[1] says:
"you must not compare resource versions for greater-than or less-than relationships".
Given so much difference, it can be beneficial to fork another simpler
AssumeCache for VolumeBinding plugin. Because of no need to send events, the
lite AssumeCache is a passive component. It only record the assumed version
without copying all objects from informer into its local cache. When reading,
we read from both informer and local cache. So it will always be up-to-date
with informer, no need to wait for event handler.
This resolves a race condition where AssumeCache and scheduler queue both
receive events from informer. When a pod is scheduling due to PV update event,
the PVCache may be not updated yet because it has not processed the relevant
event.
The passive version still listens events from informer, but only for cleaning up
its local cache to save memory.
[1]: https://kubernetes.io/docs/reference/using-api/api-concepts/#resource-versions
Kubernetes (K8s)
Kubernetes, also known as K8s, is an open source system for managing containerized applications across multiple hosts. It provides basic mechanisms for the deployment, maintenance, and scaling of applications.
Kubernetes builds upon a decade and a half of experience at Google running production workloads at scale using a system called Borg, combined with best-of-breed ideas and practices from the community.
Kubernetes is hosted by the Cloud Native Computing Foundation (CNCF). If your company wants to help shape the evolution of technologies that are container-packaged, dynamically scheduled, and microservices-oriented, consider joining the CNCF. For details about who's involved and how Kubernetes plays a role, read the CNCF announcement.
To start using K8s
See our documentation on kubernetes.io.
Take a free course on Scalable Microservices with Kubernetes.
To use Kubernetes code as a library in other applications, see the list of published components.
Use of the k8s.io/kubernetes module or k8s.io/kubernetes/... packages as libraries is not supported.
To start developing K8s
The community repository hosts all information about building Kubernetes from source, how to contribute code and documentation, who to contact about what, etc.
If you want to build Kubernetes right away there are two options:
You have a working Go environment.
git clone https://github.com/kubernetes/kubernetes
cd kubernetes
make
You have a working Docker environment.
git clone https://github.com/kubernetes/kubernetes
cd kubernetes
make quick-release
For the full story, head over to the developer's documentation.
Support
If you need support, start with the troubleshooting guide, and work your way through the process that we've outlined.
That said, if you have questions, reach out to us one way or another.
Community Meetings
The Calendar has the list of all the meetings in the Kubernetes community in a single location.
Adopters
The User Case Studies website has real-world use cases of organizations across industries that are deploying/migrating to Kubernetes.
Governance
Kubernetes project is governed by a framework of principles, values, policies and processes to help our community and constituents towards our shared goals.
The Kubernetes Community is the launching point for learning about how we organize ourselves.
The Kubernetes Steering community repo is used by the Kubernetes Steering Committee, which oversees governance of the Kubernetes project.
Roadmap
The Kubernetes Enhancements repo provides information about Kubernetes releases, as well as feature tracking and backlogs.