[BUG] CNAME resolution does not work properly

[bokysan]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

Hello,

CNAME resolution does not work.

Actual result:

1. ping: bad address 'demo.example.org'
2. nslookup works but returns ** server can't find demo.example.org: NXDOMAIN
3. dig actually works.

Expected result:

1. All three tools work

This issue arises due to incomplete or incorrect DNS resolution in Alpine’s musl libc implementation, which ping, getaddrinfo(), and others depend on. dig uses its own resolver (bypassing libc).

This wouldn't be a problem otherwise, but connecting different clients in Radarr ends up with Unable to connect to .... errors.

Expected Behavior

1. All three tools work

Steps To Reproduce

1. configure Radarr (via DOCKER) to point to an internal server (e.g. 192.168.8.1)
2. setup: demo.example.org CNAME demo2.example.org, demo2.example.org A 192.168.8.10
3. Do apk add bind-tools in the docker container
4. Try doing ping demo.example.org.
5. Try doing nslookup demo.example.org.
6. Try doing dig demo.example.org

Environment

Tested with

Linuxserver.io version: 5.26.2.10099-ls276
Build-date: 2025-06-15T04:52:48+00:00
Version 5.26.2.10099

CPU architecture

x86-64

Docker creation

  radarr:
    image: ghcr.io/linuxserver/radarr:latest
    container_name: radarr
    environment:
      - PUID=1038
      - PGID=100
      - VERSION=latest
      - TZ=Europe/Berlin
    ports:
      - 7878:7878
    labels:
      - "traefik.enable=true"
      - "traefik.http.services.radarr.loadbalancer.server.port=7878"
      - "traefik.http.routers.radarr.rule=Host(`r.example.com`)"
      - "traefik.http.routers.radarr.entrypoints=websecure"
      - "traefik.http.routers.radarr.tls.certresolver=le"
      - "traefik.http.routers.radarr-insecure.rule=Host(`r.example.com`)"
      - "traefik.http.routers.radarr-insecure.entrypoints=web"
      - "traefik.http.middlewares.radarr-insecure.redirectscheme.scheme=https"
      - "traefik.http.middlewares.radarr-insecure.redirectscheme.permanent=true"
    volumes:
      - ./radarr:/config
      # This was added as a method of trying to resolve the issue. It did not help
      - ./radarr-resolv.conf:/etc/resolv.conf:ro
      # This is the only way to resolve the issue, to hardcode the hosts
      - ./radarr-hosts:/etc/hosts:ro
      - /mnt/media/:/media
    restart: unless-stopped
    dns:
      - 192.168.8.1
    networks:
      - traefik_public
    deploy:
      resources:
        limits:
          cpus: '0.25'
          memory: 256M
        reservations:
          cpus: '0.05'
          memory: 50M
    logging:
      driver: "json-file"
      options:
        max-size: "50m"

Container logs

N/A

[github-actions]

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[j0nnymoe]

Could you provide your compose snippet you've used please?

[bokysan]

I've updated the ticket with the snipplet, although this can be easily repated via docker run --rm -it --dns=192.168.8.1 --entrypoint /bin/bash ghcr.io/linuxserver/radarr:latest -c 'ping demo.example.org'

[j0nnymoe]

What happens if you just let docker manage the DNS for you and use the hosts DNS?

[bokysan]

The same thing. The issue is with MUSL, not with Docker.

[aptalca]

Let's get some things straight. You're not trying to query a public dns. And the domain demo.example.org does not have any public CNAME or A records. You are presumably setting arbitrary values on a local dns you are running and trying to query that.

You're not able to successfully query this local dns inside the radarr container and your conclusion is that it's musl? That seems to be a bit of a leap.

Many of us use split dns. I have multiple local dns servers on my lan including unbound and adguardhome. They all work fine when queried from inside the radarr container.

This is most likely an issue specific to your setup.

You wrote configure Radarr (via DOCKER) to point to an internal server. What is this internal server? Is it pointing to the same docker host? Is it pihole running in a container? If so, that's a quite common issue folks have and that's why we don't recommend running dns in a container unless you really know what you're doing.

In any case, like I said, split dns works in radarr, so whatever issue you're having is most likely related to your setup and beyond the scope of this repo's github issues. Feel free to drop by our discord to discuss and seek help from the community.