Host env vars take precendece over task env vars with exec/raw_exec

[lgfa29]

Nomad version

Nomad v1.1.4 (acd3d7889328ad1df2895eb714e2cbe3dd9c6d82)

Operating system and Environment details

Ubuntu 20.04

Issue

When running exec or raw_exec tasks, the NOMAD_* environment variables are overwritten if they are defined in the host as well.

Reproduction steps

1 Start a Nomad agent with a NOMAD_* env var defined

$ NOMAD_ALLOC_ID=not-an-alloc nomad agent -dev

2. Run an exec/raw_exec job that prints its own env vars
3. Check value for NOMAD_ALLOC_ID

Expected Result

The allocation ID

Actual Result

The value set in the host (not-an-alloc)

Job file (if appropriate)

job "env" {
  datacenters = ["dc1"]

  group "env" {
    task "env" {
      driver = "exec"

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

      template {
        data = <<EOF
env | grep NOMAD
while true
do
  sleep 10
done
EOF

        destination = "local/script.sh"
      }

      resources {
        cpu    = 10
        memory = 10
      }
    }
  }
}

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