[CNCF LFX Proposal] Volcano/Kthena Support inPlace rolling update

### CNCF Project

Volcano

### Term

2026 Term 3 (Sep-Nov)

### Program Name

Support inPlace rolling update

### Program Description

## Description:
The existing `ServingGroupRollingUpdate` and `RoleRollingUpdate` strategies update workloads by deleting outdated resources and creating replacements. This is appropriate for arbitrary Pod template changes, but it is unnecessarily expensive when the only desired change is a container image.

Kubernetes permits updates to regular container image fields on an existing Pod. Kubelet applies the new image by restarting the affected container while retaining the Pod object and node assignment. `ModelServing` should expose this behavior as an explicit update strategy with well-defined safety, availability, recovery, and status semantics.

## Expected Outcome:
1、design Proposal(Show in the Kthena community Conference)
2、Implementation Code
3、Corresponding unit tests and end-to-end tests
4、Userguide docs

### Technologies

go/kubernetes

### Skills same as Technologies?

- [x] Yes, the required skills are the same as the technologies listed above.

### Required/Desirable Skills

_No response_

### Mentors

ZhenCheng Lee | @LiZhenCheng9527 | lizhencheng6@huawei.com | LiZhenCheng9527
JinYu Zhou | @FAUST-BENCHOU | 2319109590@qq.com | benchou8

### Upstream Issue URL

https://github.com/volcano-sh/kthena/issues/1420

### Application Prerequisites

- [x] Resume
- [x] Cover Letter
- [ ] School Enrollment Verification
- [ ] Participation Permission from school or employer
- [ ] Coding Challenge
- [ ] Custom Prerequisite (fill in details below)

### Coding Challenge URL

_No response_

### Custom Prerequisite Name

_No response_

### Custom Prerequisite Description

_No response_

### Custom Prerequisite — File Upload

- [ ] Yes — completion of this task requires the mentee to submit a file.

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**LFX program:** [CNCF - Volcano: Support inPlace rolling update (2026 Term 3)](https://mentorship.lfx.linuxfoundation.org/project/6c797658-daa1-40d6-b24c-3bf496e75755)

No source files or tests are named in this mentoring issue. Read upstream Kthena issue #1420, then inspect ModelServing and the existing ServingGroupRollingUpdate and RoleRollingUpdate strategies; done means an approved design, implementation, unit and end-to-end tests, and user-guide documentation for safe in-place image updates.

Written by the indexing model from the issue text.