Add sample Hello World Scheduled Job

[cwperks]

Description

Adds sample of a scheduled job to the HelloWorld sample Extension. The job is simple and prints Hello, World! every minute by default and the API has no configurability at the moment and cannot be de-scheduled. I plan to follow-up this PR with another that introduces an API to de-schedule the job and try to make this API more interesting.

You can call on the API with the following route:

curl -XPUT http://localhost:9200/_extensions/_hw/schedule/hello

In order to test this you need to run an OpenSearch node with the Job Scheduler plugin installed.

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[dbwiddis]

Looks like the gradle check is failing on the Job Scheduler imports. Do they need to be added to build.gradle?

[dbwiddis]

Hey @cwperks I know I suggested you contribute this here, but now that I realize it requires a dependency on job scheduler I'm wondering if that's a good idea. We want to keep SDK as minimal as possible, and adding dependencies just for hello world doesn't really help there.

• Traditionally, "hello world" is supposed to be simple. We probably want one or more larger artifacts to demonstrate more complex functionality
• There's ongoing discussion in [BUG] SDKClient implementations are not thread safe and are difficult to close #612 and [PROPOSAL] Move SDK to OpenSearch repo #616 regarding removing the client imports as well, which parallels this discussion
• I think the CRUD extension you worked on in WIP on a prototype of authorization for extension actions #118 was a good example of some of the functionality we wanted to have in a sample, and I even used it as a basis for my CRUDExtensiion that I developed as part of our CREATE_YOUR_FIRST_EXTENSION document. That's a good place (outside the SDK) to import the client...

So I definitely think we need this functionality somewhere, but I think we need to take some steps to either separate hello world from the SDK, or start clean with new extension functionality outside the SDK. I'm sure in addition to this job scheduler functionality we'll need to add in security features as well. I'm not sure what that's going to look like yet.

@owaiskazi19 @saratvemulapalli @joshpalis @ryanbogan what are your thoughts here?

[cwperks]

Hey @dbwiddis I agree that it doesn't make sense to add the dependencies only for the sample extension. If the sample extension was in another repo and it was only for the sample then that could make sense. Do you think it would be possible to include a separate build.gradle file for the sample extension that includes the dependencies?

[owaiskazi19]

Hey @cwperks! Thanks for adding the job scheduler functionality to the hello world extension. I second to what @dbwiddis has pointed above to not pull job-scheduler dependency for a sample extension. I see 2 way to move forward here:

1. Pull hello world extension to a separate repo. I don't see any problem in that. This will also help us to keep adding functionality like this one without worrying about impacting the SDK.
2. Create a separate build.gradle file for hello world extension and keep it away from SDK's build.gradle.

I'm fine with both the approaches but more inclined towards the first one!

[dbwiddis]

I see 2 way to move forward here:

1. Pull hello world extension to a separate repo. I don't see any problem in that. This will also help us to keep adding functionality like this one without worrying about impacting the SDK.
2. Create a separate build.gradle file for hello world extension and keep it away from SDK's build.gradle.

I'm fine with both the approaches but more inclined towards the first one!

Were it my private repo or a small org I control, I'd go with 1. But under the opensearch-project org, that just creates a whole new level of administrative handling, separate maintainer list, etc.

We're really doing somewhat the equivalent of the sample plugins which live underneath the OpenSearch project in their own modules. That's probably the way to go. But it also requires learning how to do gradle multimodule builds, which someone should do anyway. :)

One complicationg factor is that we do currently use helloworld tests to count toward our code coverage, so moving it elsewhere would require us to redo some tests to use an anonymous extension instead. Easily(?) done but a pain.

I propose we leave helloworld where it is, but intentionally keep it very simple. But I think we can really make our documentation awesome for future SDK users by adding this "add job scheduler functionality" to the whole "create your first extension" document, or a linked document for "next steps".

[cwperks]

Closing this for now, I will spend some time looking at a separate build.gradle file but it may take some time to figure out how to get that to properly work. There should definitely be documentation added to CREATE_YOUR_FIRST_EXTENSION on how to create an extension that schedules jobs.

[cwperks]

Re-opening this PR, I made this into a multi-module/project gradle project with the sample extension as one of the modules. It now has a separate build.gradle file so I can introduce the job-scheduler dependencies without having the SDK depend on job-scheduler.

[codecov]

Codecov Report

Merging #692 (69862c3) into main (eff7635) will decrease coverage by 3.35%.
The diff coverage is n/a.

❗ Current head 69862c3 differs from pull request most recent head 9f805c2. Consider uploading reports for the commit 9f805c2 to get more accurate results

@@             Coverage Diff              @@
##               main     #692      +/-   ##
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- Coverage     43.57%   40.22%   -3.35%     
+ Complexity      314      269      -45     
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  Files            69       61       -8     
  Lines          1983     1857     -126     
  Branches        141      133       -8     
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- Hits            864      747     -117     
+ Misses         1101     1096       -5     
+ Partials         18       14       -4     

see 21 files with indirect coverage changes