Local container-based DNS cannot resolve on some Linux systems.

If you, for example have a container service in docker-compose named elasticsearch, it is not resolvable through local DNS on some distributions of Linux.

More specifically, Ubuntu is impacted by this issue where Arch Linux is now, though independent testing should be carried out on MacOS to achieve parity.

The root cause of problem is because of the default Resolver configuration being provided on Ubuntu is different than Arch.

To do's

I have been wanting to fix this for a while, so now is as good of a time as any.

Provide examples of the Resolver configuration file causing issues, and not causing issues.
Provide a docker-compose.yml file that is testable.
Determine the impact for currently supported MacOS versions.
PR for a fix for this change on Linux and if appropriate MacOS
CI tests for this change ensuring nothing is impacted by the PR (not strictly needed), and to show that container DNS does resolve.

Evidence of a working system

cli-drupal:/app$ curl opensearch:9200
{
  "name" : "4a0a84aab61c",
  "cluster_name" : "docker-cluster",
  "cluster_uuid" : "KHuKDDCIT3OVV-Y-ZFQ8Ng",
  "version" : {
    "distribution" : "opensearch",
    "number" : "2.17.0",
    "build_type" : "tar",
    "build_hash" : "8586481dc99b1740ca3c7c966aee15ad0fc7b412",
    "build_date" : "2024-09-13T01:04:14.707418737Z",
    "build_snapshot" : false,
    "lucene_version" : "9.11.1",
    "minimum_wire_compatibility_version" : "7.10.0",
    "minimum_index_compatibility_version" : "7.0.0"
  },
  "tagline" : "The OpenSearch Project: https://opensearch.org/"
}

Source: https://github.com/lagoon-examples/drupal-opensearch

I'm not able to reproduce the problem... again.

I'll leave this one open in case somebody can provide more information.

Users affected by this change can find the Resolver file specific to Pygmy in the following path /usr/lib/systemd/resolved.conf.d. What I'd like to see is some sort of networking config - be it resolv or NetworkManager which demonstrates why this issue is causing a problem. All indications dealing with this in the past seems to isolate it to the default configuration under Ubuntu systems.

The situation I know happens for some people looks like the following, but the service name & port might be different:

$ curl opensearch:9200
curl: (6) Could not resolve host: opensearch

pygmystack / pygmy

Local container-based DNS cannot resolve on some Linux systems. #585