access postgres in kubernetes from an application outside the cluster

Ingress won't work, it's only designed for HTTP traffic, and the Postgres protocol is not HTTP. You want solutions that deal with just raw TCP traffic:

• A NodePort service alone should be enough. It's probably the simplest solution. Find out the port by doing kubectl describe on the service, and then connect your Postgres client to the IP of the node VM (not the pod or service) on that port.
• You can use port-forwarding: kubectl port-forward pod/your-postgres-pod 5432:5432, and then connect your Postgres client to localhost:5432. This is my preferred way for accessing the database from your local machine (it's very handy and secure) but I wouldn't use it for production workloads (kubectl must be always running so it's somewhat fragile and you don't get the best performance).
• If you do special networking configuration, it is possible to directly access the service or pod IPs from outside the cluster. You have to route traffic for the pod and service CIDR ranges to the k8s nodes, this will probably involve configuring your VM hypervisors, routers and firewalls, and is highly dependent on what networking (CNI) plugin are you using for your Kubernetes cluster.