Create a working Java-based user image

[shaneknapp]

if possible, continue to refine the java user image in to something that's workable.

[shaneknapp]

latest candidate: #7

i'll deploy this to the demo hub on monday.

[shaneknapp]

alright, i did a bit of work over the weekend, and while java/javac/etc all seem to work great, there were issues w/vscode.

you can open one vscode window and everything works perfectly. however, if you open a 2nd (via the jupyterlab launcher), both vscode sessions would hang, the number of ephemeral ports on the chp node would more than double, and eventually your kernel would crash:

[18:16:28] [127.0.0.1][42ffb0c4][ExtensionHostConnection] <409> Launched Extension Host Process.
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 40
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 41
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 42
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 43
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 44
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 45
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 46
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 47
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 48
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 49
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 50
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 51
[18:16:29] RequestStore#acceptReply was called without receiving a matching request 52
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 53
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 54
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 55
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 56
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 57
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 58
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 59
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 60
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 61
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 62
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 63
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 64
[18:16:30] RequestStore#acceptReply was called without receiving a matching request 65

however, with the latest changes that i merged, this no longer seemed to happen (assuming it may have been the websockify and appmode python packages that fixed it?) locally. i'm about to test this again: #9

[shaneknapp]

just merged #10 which works locally on my workstation

[shaneknapp]

the "recommended" java plugin for vscode has a massive memory leak and has henceforth banned from our image. for now.

#12

i've set up https://demo.jupyter.cal-icor.org for testing. vscode works, and doesn't OOMKill the singleuser server when you open two sessions w/terminals. i also bumped the user ram to 2G... java uses ram, and we need to take this in to account when scheduling nodepools.

[sean-morris]

thanks for all this! I will use it all next semester and start telling people about it.

[shaneknapp]

this is a "please kick the tires" deployment. i have a LOT of experience dealing w/java insanity from my time in @apache/spark. it's a much more complex ecosystem when you want to set up a reproducible build environment, and i can just image what a dev environment would look like... the possibilities w/regards to what version of java from whatever provider, plus the big differences between major releases and compatibility mean that we can only really support the bare minimum of a java image config... plus spotty support from provider-supported, but broken vscode plugins. basically, we need a consensus of some power users over what version jdk we use etc. the newer the better imo. also how they plan to teach. which of course people who actually know java will pick any of those hills to die on lol... :)

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On Mon, Dec 8, 2025 at 6:32 PM sean-morris ***@***.***> wrote: *sean-morris* left a comment (cal-icor/java-user-image#6) <#6 (comment)> thanks for all this! I will use it all next semester and start telling people about it. — Reply to this email directly, view it on GitHub <#6 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAMIHLFIWAH3YO4YFY4HSW34AYYB7AVCNFSM6AAAAACESWCXPCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMMRZHEZTKNRSGI> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[sean-morris]

in terms of classroom use, the standard set of settings is fine especially for High School -- no spark deployments here! The first semester college type course is very basic stuff. Thanks for all this

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On Mon, Dec 8, 2025 at 6:48 PM shane ***@***.***> wrote: *shaneknapp* left a comment (cal-icor/java-user-image#6) <#6 (comment)> this is a "please kick the tires" deployment. i have a LOT of experience dealing w/java insanity from my time in @apache/spark ***@***.***> and it's a much more complex ecosystem when you want to up a reproducible build environment, and i can just image what a dev environment would look like... the possibilities w/regards to what version of java from whatever provider, plus the big differences between major releases and compatibility mean that we can only really support the bare minimum of a java image config... plus spotty support from provider-supported, but broken vscode plugins. basically, we need a consensus of some power users over what version jdk we use etc. the newer the better imo. also how they plan to teach. which of course people who actually know java will pick any of those hills to die on lol... :) On Mon, Dec 8, 2025 at 6:32 PM sean-morris ***@***.***> wrote: > *sean-morris* left a comment (cal-icor/java-user-image#6) > < #6 (comment)> > > thanks for all this! I will use it all next semester and start telling > people about it. > > — > Reply to this email directly, view it on GitHub > < #6 (comment)>, > or unsubscribe > < https://github.com/notifications/unsubscribe-auth/AAMIHLFIWAH3YO4YFY4HSW34AYYB7AVCNFSM6AAAAACESWCXPCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMMRZHEZTKNRSGI> > . > You are receiving this because you authored the thread.Message ID: > ***@***.***> > — Reply to this email directly, view it on GitHub <#6 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AALR3445U3LFHKO3JRZEM4T4AY2AVAVCNFSM6AAAAACESWCXPCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMMRZHE3TGMZZHE> . You are receiving this because you were assigned.Message ID: ***@***.***>

[shaneknapp]

just be sure that no one installs the vscjava.vscode-java-pack extension! :)