[Feature][history server] support endpoint /timezone

[CheyuWu]

Why are these changes needed?

we need to support something like this for dead cluster using golang.

https://github.com/ray-project/ray/blob/9cbcdb468904f8aa8122b817be216e0da237c086/python/ray/dashboard/timezone_utils.py#L1-L56

Summary

This PR adds timezone metadata collection and API support to the KubeRay history server, enabling proper timestamp interpretation for historical Ray cluster sessions.

Changes Overview

Commit 1: Collector-side timezone metadata collection (5f7600f)

Added timezone information collection in the log collector component:

Data Structure

• Introduced timezoneInfo struct with two fields:
  • Offset: UTC offset string (e.g., "+08:00")
  • Value: IANA timezone name (e.g., "Asia/Shanghai")

Timezone Detection Strategy

• Fetches timezone from the Ray Dashboard endpoint (GET {DashboardAddress}/timezone)
• If the dashboard is unavailable, the write is skipped (no local fallback)

Storage

• Writes timezone metadata to {clusterDir}/{session}/fetched_endpoints/restful__timezone following the same storage path convention as FetchAndStoreClusterMetadata
• Called in three locations:
  • processSessionLatestLogs
  • processSessionPrevLogs
  • WatchSessionLatestLoops

Testing

Added unit tests including:

• Mock HTTP client to simulate dashboard responses
• Test case verifying that when the dashboard is unavailable, no file is written
• Test case for dashboard-based timezone fetching (Asia/Seoul)

Commit 2: History server API endpoint (6551317)

Exposed timezone metadata through a REST API:

New Endpoint: GET /timezone

• Returns session-specific timezone metadata for historical sessions
• Redirects to live cluster if session is "live"
• Returns {"offset":"","value":""} if metadata file doesn't exist
• Returns actual timezone data if metadata is found

Implementation

• Reads from storage path {clusterNameID}/{sessionName}/fetched_endpoints/restful__timezone
• Returns the JSON content directly

Manual Testing

Follow the instruction to create the live cluster

https://github.com/ray-project/kuberay/blob/master/historyserver/docs/set_up_historyserver.md

Get live cluster timezone

$ curl -c ~/cookies.txt "http://localhost:8080/enter_cluster/default/raycluster-historyserver/live"
{
 "name": "raycluster-historyserver",
 "namespace": "default",
 "result": "success",
 "session": "live"
}
$ curl -b ~/cookies.txt "http://localhost:8080/timezone"
{"offset": "-08:00", "value": "America/Los_Angeles"}

File in MinIO

• 

Get Dead cluster timezone

Delete the raycluster

$ kubectl delete -f historyserver/config/raycluster.yaml

Clean the cookies

$ rm ~/cookies.txt 

Read dead cluster

$ curl "http://localhost:8080/clusters"
[
 {
  "name": "raycluster-historyserver",
  "namespace": "default",
  "sessionName": "session_2026-02-14_08-35-24_859677_1",
  "createTime": "2026-02-14T08:35:24Z",
  "createTimeStamp": 1771058124
 }
]

Get cookies

$ curl -c ~/cookies.txt "http://localhost:8080/enter_cluster/default/raycluster-historyserver/session_2026-02-14_03-06-40_606126_1"
{
 "name": "raycluster-historyserver",
 "namespace": "default",
 "result": "success",
 "session": "session_2026-02-14_08-35-24_859677_1"
}

Get dead cluster timezone

$ curl -b ~/cookies.txt "http://localhost:8080/timezone"
{"offset":"-08:00","value":"America/Los_Angeles"}

Log in historyserver

$ k get pods
NAME                                  READY   STATUS      RESTARTS      AGE
historyserver-demo-64bd94bc79-h66wk   1/1     Running     0             2m19s
kuberay-operator-94fcdcd69-h8hp4      1/1     Running     4 (22m ago)   7d8h
rayjob-ns5r8                          0/1     Completed   0             101s

$ k logs historyserver-demo-64bd94bc79-h66wk

Related issue number

Closes #4503

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

[Future-Outlier]

Hi, @CheyuWu can you help me follow this PR's pattern?
#4519

[CheyuWu]

Hi, @CheyuWu can you help me follow this PR's pattern? #4519

OK no problem

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

[CheyuWu]

Hi @Future-Outlier, I have address the problem you have mentioned, and rewrite the code PTAL

[justinyeh1995]

Suggested change

	path.Base(sessionID),
	sessionID,

do we really need path.Base here?