replication design and implementation for a postgres DB on windows for C# web api application

we have a web api application that is installed and running on a server (postgres is installed on same server). the idea now is to run same webapi on the second server(install postgres also there). and make it redundant for the primary server.
so whenever a data is written on first server it will be automatically replicated to the secondary and in case primary server is down.. secondary will take place till primary is back up again