Implementing failover logic is quite simple, and probably even preferred over a pre-built solution because you can implement it in the way that integrates well with your architecture.
The basic logic is as follows:
On the standby server you would configure the "trigger" file. When you create a trigger file with the name you specify the standby will promote to master.
You have your queries send to the master.
If your application starts failing to connect to the master you would have logic evaluate why
When the master goes down you should
Generate a trigger file to promote the standby to master
Modify your DNS entries to have your applications point to the new master
The most common configuration is to use PostgreSQL's built in master/standby streaming replication. However you will need to develop any fail-over logic you need yourself or use a third party tool such as EnterpriseDB's Failover Manager.
