How to update environment variable dynamically in Hashicorp Nomad deployment

Question

I have a series of micro services developed in .NET 6 that I'm going to migrate to Hashicorp Nomad.

From my A microservice I have to call my B service.

Every microservice is registered in Consul in order to user Service Discovery feature.

A has this appsettings.json configuration in order to call other services:

{
  "ExternalServices": [
    {
      "Name": "ExternalSimple-Test",
      "Url": "",
      "ClientId": "myAzureClientId",
      "Scopes": [
        "myAzureScope"
      ]
    },
    ...
]}

I retrieve these configuration using IOptionSnapshot in my .NET class in order to be re-evaluated and updated.

The URL must be configured from the Nomad HCL deployment file in order to use realtime Consul address and port.

Do someone has some idea and provide me an example how to set these Urls from HCL file dynamically querying Consul?

Thank you,
Dave.

Answer 1

You can utilize Consul's DNS interface. This approach allows your microservices to resolve service addresses and ports at runtime through DNS queries. In the nomad job spec put env:

  env {
    SERVICE_B_URL = "http://service-b.service.consul:PORT"
  }

References: https://developer.hashicorp.com/consul/docs/services/discovery/dns-overview