UPF container fails when hostname is provided as MBS UDP tunnel address

[devbbc]

When the MB UPF is configured to create an UDP tunnel, it works if an IP address is provided in the configuration. However, the MB UPF fails to resolve hostname is provided in the configuration.

Test environment

Containerised 5G MBS system instantiated using artifacts from rt-mbs-examples repository along with containerised MBSF and MBSTF.

UPF configuration

logger:
  file:
    path: /var/log/open5gs/upf_mb-upf.log

global:

upf:
  pfcp:
    server:
      - address: upf-mb-upf.5g-mag.org
    client:
  gtpu:
    server:
      - address: upf-mb-upf.5g-mag.org
  session:
    - subnet: 10.45.0.0/16
      gateway: 10.45.0.1
  mbs:
    udptunnel:
      address: upf-mb-upf.5g-mag.org
      port: 0

Error

$ sudo docker compose -f compose-files/internal/docker-compose-mbs.yml --env-file=.env logs upf_mb-upf
upf_mb-upf  | Open5GS daemon v2.7.2
upf_mb-upf  | 
upf_mb-upf  | 07/16 11:14:34.319: [app] INFO: Configuration: '/etc/open5gs/custom/upf_mb-upf.yaml' (../lib/app/ogs-init.c:144)
upf_mb-upf  | 07/16 11:14:34.319: [app] INFO: File Logging: '/var/log/open5gs/upf_mb-upf.log' (../lib/app/ogs-init.c:147)
upf_mb-upf  | 07/16 11:14:34.365: [upf] ERROR: Cannot resolve 'upf-mb-upf.5g-mag.org' as an address for upf/mbs/updtunnel/address (../src/upf/context.c:201)
upf_mb-upf  | 07/16 11:14:34.365: [app] ERROR: Failed to initialize UPF (../src/upf/app.c:28)
upf_mb-upf  | 07/16 11:14:34.365: [app] FATAL: Open5GS initialization failed. Aborted (../src/main.c:228)

[devbbc]

A work around solution is to add an extra function in rt-mbs-examples/mbs-docker-setup/images/upf_mb-upf/helper_functions.sh to resolve the hostname to IP address and create a configuration file with that IP address.
Then in entrypoint.sh, start open5gs-upfd with the newly created configuration file.

[devbbc]

A cleaner approach is to modify src/upf/context.c in the MB-UPF to handle hostname as well.

I am working on this fix and will contribute a PR to the 5mbs-development branch of the open5gs project.