I have a doubt that every container has its own ip address. Is the localhost will work inside the containers.
Are you asking this in the context of Testcontainers or in general?
In general, yes, every container has its own local IP address accessible only from that machine (by default) and no, localhost is not the same in the container as outside the container, but whether it would work or not, depends on what you are doing exactly. If something is listening only inside the container on localhost, that will not be available outside the container even if you use the container IP. Porcesses in the container usually need to listen on all available IP addresses in the container: 0.0.0.0
What is your goal?.