Can not share the data between tasks: alloc folder is not visible for template section

[EugenKon]

Nomad version

v1.8.0

Issue

I am trying to share the data between tasks. Because first task is exec and second task is docker the alloc folder is mounted directly into container https://developer.hashicorp.com/nomad/docs/runtime/environment#task-directories and is not visible to template block of second task.

Reproduction steps

Create two tasks, first one is 'prestart' and stores some data into alloc folder. The second task is a docker and tries to read data from the 'alloc` folder at template section.

Expected Result

'alloc' should be visible from 'template' section for the task of 'docker' type.

Actual Result

The folder is not visible and data could not be shared.

Job file

Job file

job "postgres" {
  region = "xxx"
  datacenters = ["dc"]
  type = "service"

  group "postgres-db" {
    count = 1

    network {
      port "postgres-db" {
        static = 5432
        to     = 5432
      }
    }

    task "prepare-credentials-task" {
      lifecycle {
        hook = "prestart"
        sidecar = false
      }

      driver = "exec"

      config {
        command = "/bin/bash"
        args    = ["local/script.sh"]
      }

      template {
        destination = "local/script.sh"
        data        = <<-EOH
          set -ex

          cat <<CREDS > $NOMAD_ALLOC_DIR/creds.env;
          INITIAL_PASSWORD=${INITIAL_PASSWORD}
          CREDS
        EOH
      }
    }

    task "postgres-task" {
      driver = "docker"

      config {
        force_pull = false
        image = "xxx/userdb:v15"
        ports = ["postgres-db"]
      }

      template {
        env         = true
        destination = "secrets/file.env"        
        # data        = file("$NOMAD_ALLOC_DIR/creds.env")
        data        = <<-EOH
          {{ $file :=  file "$NOMAD_ALLOC_DIR/creds.env" }}
          {{ range $line := split "\n" $file }}
            {{ $parts := split "=" $line }}
            {{ if eq (len $parts) 2 }}
              {{ env (index $parts 0) (index $parts 1) }}
            {{ end }}
          {{ end }}
        EOH
      }
    }
  }
}

[tgross]

Hi @EugenKon! The environment variable $NOMAD_ALLOC_DIR doesn't exist in the context of the template runner, which is running in the host's environment. You'll need to do something like the following instead:

task "postgres-task" {
  driver = "docker"

  config {
    force_pull = false
    image      = "xxx/userdb:v15"
    ports      = ["postgres-db"]
    command    = "/local/start.sh"
  }

  template {
    env         = true
    destination = "local/start.sh"
    data        = <<-EOH
source $NOMAD_ALLOC_DIR/creds.env
exec /path/to/postgres --arg1 --arg2
EOH
  }
}

[EugenKon]

This looks like a hack, but thanks.

[EugenKon]

@tgross How to deal with this if pre-start task fetches/generates template for nginx and we need to restart nginx if service list was changed?

    task "wi-nginx-task" {
      driver = "docker"

      config {
        force_pull = false
        image = "nginx"

        volumes = [
          "custom/xxx.nginx.conf:/tmp/nginx/sites-enabled/xxx",
        ]
      }

      template {
        source = "$NOMAD_ALLOC_DIR/generated"
        destination = "custom/xxx.nginx.conf"
        change_mode = "restart"
      }
    }

[EugenKon]

It looks like I need artifact { script = XXX } option.