Docker unbound

Please share ideas.
I've setup pi-hole and unboud (custom image) with docker. All forks fine, but with workaround. I've added static IP to unbound container because its impossible to add FQDN as custom DNS server.

docker-compose.yml

networks:
....
  dns:
    name: dns
    ipam:
      driver: default
      config:
        - subnet: "192.168.12.0/24"
...
services:
...
pihole:
    container_name: pihole
    image: pihole/pihole:latest
    hostname: home
...
    networks:
      - main
      - dns
...
 unbound:
    container_name: unbound
    image: unbound-alpine
    pull_policy: never
    networks:
      dns:
        ipv4_address: 192.168.12.254
....

Dockerfile

FROM alpine:latest
RUN  apk add --no-cache unbound
COPY unbound.conf /etc/unbound/unbound.conf
WORKDIR /etc/unbound/
EXPOSE 53
EXPOSE 53/udp
CMD ["unbound", "-c", "/etc/unbound/unbound.conf", "-d"]

What's the issue exactly?