How to define a parameterized periodic nomad job

Nomad
1

I am looking for an example of parameterized periodic job definition. Below is what I tried unsuccessfully.

job "job-name-move" {
  region = "region"
	datacenters = ["datacenter"]
  node_pool = "default"
  type = "batch"
 
  parameterized {    
    payload = "forbidden"
    meta_required = ["PROC_TYPE"]
  } 
  periodic {
    crons             = ["* * * * * *"]
    prohibit_overlap = true
  }    
  group "job-name-grp" {
    
    constraint {
      attribute = "${node.class}"
      operator  = "="
      value     = "etl"
    }
     

    task "job-name-task" {
      driver = "raw_exec"
      config {
        command  = "C:\\python\\python39\\python.exe"
        args     = ["C:\\run.py", "-p", "${NOMAD_META_PROC_TYPE}"]
      }
    }
  }
}

What I see is that I got a parameterized job, and after I dispatch it with META PROC_TYPE, it creates child job which is periodic, but that job remains “Unplaced”. If I remove the “periodic” block, then I could dispatch the parameterized job with META_PROC_TYPE and the task would get executed correctly once. If I remove the parameterized block and define a meta, then the job also gets executed correctly.

I am looking for:

  1. An example for a paramterized and peridoic job
  2. Can I make the cron schedule also a meta (paramter) of the job?
2

Hi @dhuang-vf,

Can you try removing one asterisk (*) from your cron definition?

Just write ["* * * * *"] (5 asterisks instead of 6). This would also evaluate well in Crontab.guru - The cron schedule expression generator* (evaluates every minute).

Concerning your questions:

  1. I have an example for my snapshot schedule (which is also parameterized) at nomad-snapshots.nomad - nomad - HCL and Docker files for Nomad deployments
  2. First I thought that should work, since "* * * * *" should be just a string? But when I tried this I had en error message (kept the rest as is, just changed the parameters and the cron schedule):
  parameterized {    
    payload = "forbidden"
    meta_required = ["PROC_TYPE", "crons"]
  }
  periodic {
    # variable here is uppercase, even with lowercase input param
    crons             = [NOMAD_META_CRONS]
    prohibit_overlap = true
  }

I had this error (so no, it did not work as I expected):

nomad plan nomad-snapshots-2.nomad 
Error during plan: Unexpected response code: 500 (1 error occurred:
        * 1 error occurred:
        * Invalid cron spec "${NOMAD_META_CRONS}": missing field(s))

I also tried with crons = ["${NOMAD_META_CRONS}"] but had the same error. It seems to work fine in another section of the job spec, for example, group > task > config > args, as you can see in my snapshot example (1).

Seems like the periodic > crons stanza is evaluated before any parameters are considered, hence, the error.

Cheers

3

I just realized it would also work with six asterisks, since they implemented the “seconds” as well (GitHub - hashicorp/cronexpr: Cron expression parser in Go language (golang)).