Force envoy proxy to use internal network

I’m using nomad to run a postgres along a rails webserver on docker and I connect them with sidecar proxies. I therefore declared an “internal” network ( in the nomad.hcl.
Using it in the network/port-stanza results in running the docker instances of postgres and rails in the internal network.
The connect-proxy container created by envoy run on the external (default) network. Is there a way to force envoy to use the internal network, too?