Dockerized app can not reach ucs-sso

ucs is running in virtual box - only one primary instance.

the primary instance has the two default dns / ips:

  • ucs-5-primary.qua-dev-test.intranet/ →
  • ucs-sso.qua-dev-test.intranet/ →

From the primary console both urls are reachable (no changes made to ucs dns/networking).
From docker containers the ucs-5-primary.qua-dev-test.intranet/ - e.g. is reachable - thus connection via ucs-5-primary.qua-dev-test.intranet:7389 is working fine.

But connection via saml does not work:

´´´err: Get “ucs-sso.qua-dev-test.intranet/simplesamlphp/
saml2/idp/metadata.php”: dial tcp connect: no route to host´´´

note that within docker containers the dns works fine: ucs-sso.qua-dev-test.intranet → resolves to… but the app in the container can not connect to the ip address.

i already tried to add network_mode: host for each container in the docker-compose.yaml, but it seems that ucs / docerk 17 ist not capable of creating all containers with network_mode host and tries to install a bridge network.

Question: how can apps in docker containers reach the ucs-sso?