Rover CLI routing_url env var

[cluedtke]

Just an idea that I would benefit from in my situation. We have multiple availability zones, each with an instance (and a different URI) of our apollo gateway. I don't think this is possible in the current rover/supergraph builds, but it would be great to configure our supergraph with env vars to use for routing to subgraphs.

For example, in supergraph.yaml, provide a routing_url_var that can be set in place of routing_url.

Edit:

I just realized routing_url does not need to be an actual URL. So to get around, I was able to, e.g. provide a routing_url of var.SUBGRAPH_1_URL, and then in builldService() override, check for that convention and instead pull from process.env, e.g.

buildService({ url }) {
  if (url.startsWith("var.")) {
    url = process.env[url];
  }
 return new RemoteGraphQLDataSource({ url });
}