The idiomatic way to achieve this is to use the service name as hostname and the port the service is exposing.
When in the same namespace, the service name alone is enough. I.E.
my-service-name:8080
When in different namespaces, you can append the namespace to the service name as its part of the container's fully qualified domain name. I.E.
my-service.my-namespace:8080
Additionally, many tools and even the browser is using default ports. So if you were to expose your service on port 80 and wanted to reach it over HTTP with let's say curl, you could omit the port since curl would use port 80 by default.
curl my-service
Note that in this instance even the protocol is left out, as curl uses HTTP by default. If you wanted to connect over HTTPS on port 8080 to a service, then you would need to provide both protocol and port.
curl https://my-service:8080
This is because, Kubernetes runs its own DNS resolver. To learn more about this, you can maybe look at this question.
Why dig does not resolve K8s service by dns name while nslookup has no problems with it?
Furthermore, it is a common pattern to use environment variables for your container to set the URI to connect to other services. That has the benefit of being able to deploy your service everywhere without having to know how the other service may be reachable upfront. Otherwise, you would potentially need to rebuild the container, if something outside such as service name or port has changed.
