[Nomad] Use client side variables.

app.py

from flask import Flask
import os

app = Flask(__name__)

@app.route("/", methods=["GET"])
def root():
    return os.getenv("DOMAIN", "None")

if __name__ == "__main__":
    app.run(host="0.0.0.0")

client1.hcl

client {
    enabled = true
    servers = [ "ipaddress" ]
    meta {
        domain="This is domain value."
    }
}

Dockerfile

FROM python:latest
RUN pip install flask
COPY ./app.py /root/app.py
CMD python /root/app.py

web-app.nomad

job "web-app"{
    datacenters = ["dc1"]
    type = "system"
    update {
        stagger = "10s"
        max_parallel = 1
    }
    task "webservice" {
        driver = "docker"

        config {
            image = "flask-app:1.2.0"
            port_map {
                web = 5000
            }
        }
        resources {
            network {
                port "web" {}
            }
        }
        env {
            DOMAIN = "${meta.domain}"
        }
    }
}