Add monitor for Zookeeper

[AayuStark007]

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Description

I have some zookeeper hosts that I want to monitor. So, I decided to use uptime-kuma, but it does not have a dedicated monitor for zookeeper instances. This PR adds that support by using node:net module to do echo ruok | nc <host> <port> and checks for imok response.

PS: I tried using TCP, but it always gives a UP status if the instance is running, but the zookeeper process is down. Hence the need for this monitor.

Caveat:
The below feature only supports zookeeper versions 3.3.0+
In order for the monitoring to work, the zookeeper process should have 4lw command ruok permitted via the 4lw.commands.whitelist configuration option.

Fixes #(issue)

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas (including JSDoc for methods)
• My changes generates no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)

[louislam]

It will be accepted, but currently we are working on 2.0.0 and there are a lot of pull requests that are waiting for review.

It may take some to be merge. Maybe in 2.2.0.

You can check the current progress here:
https://github.com/louislam/uptime-kuma/milestones

[AayuStark007]

Sure, I can wait for the 2.2.0 release. I have already implemented the feature for my use case, and I wanted to contribute them back to the main project.
So, proceeding from here, do I:

• push my changes to this PR? or raise one separately
• should I add all the code as part of a single PR, or is it better to have frontend and backend changes as separate PRs?

[louislam]

Put it here and a single PR is preferred, so that we don't need to checkout two PRs in order to test it.

[louislam]

Please note that it cannot pass the ARM64 test, probably due to native build issue.

You may need to find another library or find a way to pre-build that.

[AayuStark007]

Sure, I'll replace the zookeeper dependency with netcat. I only need to run the equivalent of echo ruok | nc localhost 2181 for the monitor to work. netcat is a pure js library, so it will not have native build issues.

[AayuStark007]

I realized I could simply use the inbuilt node:net module to do the same. This will remove any dependency on 3rd party library.

[CommanderStorm]

Thanks for the PR
I have gone trough this monitor and have left inline comments where things need to be changed ^^

[CommanderStorm]

Please use the hostname and timeout fields instead.
I don't see a reason why we shoud add these fields ^^

[CommanderStorm]

We have recently started using a better syntax for creating monitors.
It is documented in our contribution guide here:
https://github.com/louislam/uptime-kuma/blob/master/CONTRIBUTING.md#:~:text=new%20monitoring%20types

The currently migrated montiors live here:
https://github.com/louislam/uptime-kuma/tree/master/server/monitor-types

All new monitors MUST to use this, to use this format instead.
Rationale: We can't keep dumping all code in the giormous monitor.js. This does not scale in terms of maintenance/.. effort.

[CommanderStorm]

Please include a helptext about what you mentioned in the PR-description.
Currently, a user might just think it is not working, right?