Duplicate job block error when using nomad-pack plan for cron jobs

[FirstPiterSky]

Description: We are encountering a 400 error when attempting to create tasks in Nomad using the nomad-pack plan command. The error is related to duplicate job blocks in the rendered job file.

Steps to Reproduce:

• use any template to generate the job file:

[[ range $key, $ObjAll := var "jobs" . ]]
job "[[ var "job_prefix" $ ]]_cron_[[ $ObjAll.name ]]" {
~~~~~
[ [- end ]]

• render command works successfully

./nomad-pack render ./cron --var-file="./cron/cron.hcl" --to-dir ./out

• Run the following command:

./nomad-pack plan ./cron --var-file="./cron/cron.hcl"

• Error message is as follows:

! Failed To Parse Job Specification

    Error:   Unexpected response code: 400 (Failed to parse job: input.hcl:164,1-48: Duplicate job block; Only one block of type "job" is allowed. Previous definition was at input.hcl:2,1-32.
input.hcl:326,1-59: Duplicate job block; Only one block of type "job" is allowed. Previous definition was at input.hcl:2,1-32.
input.hcl:488,1-34: Duplicate job block; Only one block of type "job" is allowed. Previous definition was at input.hcl:2,1-32.
~~~~~
input.hcl:3890,1-45: Duplicate job block; Only one block of type "job" is allowed. Previous definition was at input.hcl:2,1-32.
input.hcl:4052,1-45: Duplicate job block; Only one block of type "job" is allowed. Previous definition was at input.hcl:2,1-32.)
    Context: 
        - Template Name: fita_cron/templates/cron.nomad.tpl
        - Registry Name: <<local folder>>
        - Pack Name: cron
        - Pack Ref: <<none>>
        - Pack Path: /worckflow/fita/deploy/nomad/packs/cron
        - Deployment Name: cron

Expected Behavior: The job specification should be parsed and tasks should be created successfully in Nomad.

Actual Behavior: The command fails with a 400 error due to multiple "job" blocks in the generated file.

[pkazmierczak]

Hi @FirstPiterSky, thanks for reporting this issue. We'll look into it!

[tgross]

Hi @FirstPiterSky! This fell thru the cracks a bit in the triage process, sorry about that. This is expected behavior. Suppose I have a pack like the following:

template file file

[[ range $key, $ObjAll := var "jobs" . ]]
job "[[ var "job_prefix" $ ]]_cron_[[ $ObjAll ]]" {

  group "app" {
    type = "batch"
    task "server" {
      driver = "raw_exec"

      config {
        command = "/bin/bash"
        args = ["-c", "sleep", "100"]
      }
    }
  }
}

[[- end ]]

var file

variable "job_prefix" {
  description = "The prefix"
  type        = string
  default     = "example"
}

variable "jobs" {
  description = "A list of jobs"
  type        = list(string)
  default     = ["foo", "bar"]
}

If I render that, I get something like the following:

$ nomad-pack render --to-dir out/ .
example/example.nomad:


job "example_cron_foo" {

  group "app" {
    type = "batch"
    task "server" {
      driver = "raw_exec"

      config {
        command = "/bin/bash"
        args    = ["-c", "sleep", "100"]
      }
    }
  }
}
job "example_cron_bar" {

  group "app" {
    type = "batch"
    task "server" {
      driver = "raw_exec"

      config {
        command = "/bin/bash"
        args    = ["-c", "sleep", "100"]
      }
    }
  }
}

But if I check the contents of the out directory, I'll see that both jobs have been mashed together in a single jobspec file. That's not permitted by Nomad's parser -- you can only have one job per jobspec. If you want multiple jobs in a pack, you need to define them as separate template files. You can see an example of this in this pack which runs two different jobs.

Rendering to disk via --to-dir is in general going to be a pretty good way to debug problems, because at the end of the day the jobspecs generated by Pack to be a valid Nomad jobspec.