Docs bug - os_service is not implemented on linux.

[the-maldridge]

Overview of the Issue

The documentation clearly states that os_service supports both windows and systemd service types. However systemd support is unimplemented. Either the docs should be updated to reflect reality, or the support should be implemented.

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Reproduction Steps

Consul info for both Client and Server

N/A

Operating system and Environment details

Debian 11, amd64.

Log Fragments

Oct 02 18:12:15 consul-demo1 consul[14100]: 2023-10-02T18:12:15.469Z [ERROR] agent: error creating OS Service client: error="not implemented"

[im2nguyen]

@david-yu can you help confirm this? i can update the docs to reflect the current functionality

[jkirschner-hashicorp]

Only windows is supported, not systemd/unix. The documentation is inaccurate*.

Reference: The os_service_unix.go source file makes it clear that unix isn't supported yet. The original PR intentionally only addressed this for Windows.

*The original PR author probably felt the docs were accurate, because you technically can specify a SystemD type... but if you do that, you'll get "not implemented" errors.

[the-maldridge]

While technically accurate, this is not the expectation I hold as an end user. Per the principle of least surprise, if something is flagged as a supported option I would expect that configuring it does not result in an error.

[jkirschner-hashicorp]

Totally agree @the-maldridge. Technically correct is the worst kind of correct ;)

Out of curiosity, what are you doing instead (since the OS Service health check type doesn't exist for Linux)? And how adequate of an alternative is that?

If I remember correctly, we implemented OS Service health checks on Windows primarily because trying to do the equivalent with a script check had a really high overhead on Windows, whereas it didn't on Linux. More details here.

[the-maldridge]

I use just an http service check, but I've occasionally had that return interesting results, so I was wanting to enable OS checks as well so that I could alert on the condition where systemd thinks something is up but the service itself disagrees.

[vftaylor]

Hello lovely people. Awaiting this to be implemented on Linux, but in the meantime @the-maldridge @jkirschner-hashicorp for anyone that comes across this you can simply use a script check e.g.:

{
  "service": {
    "name": "dhcp",
    "check": {
      "args": ["/usr/bin/systemctl", "is-active", "kea-dhcp4-server"],
      "interval": "10s"
    }
  }
}