Just to add a bit on Jeff's comments and to make it more clear about what happens when one server dies in your situation.

During normal operation, your b0 will run your database and your b1 will run your application server (or vice versa). So both boxes will perform their roles just like they do now.

In case your b0 fails, the box b1 will take over its database service and it will handle both application server and the database untill you fix your box b0, when everything goes back to normal.

Similarly, in case your box b1 dies, b0 will take over its load, running both database and application server untill b1 is repaired.

This is so called active-active configuration. In this configuration it is advisable that both boxes have sufficient free resources during normal operation, so that they can take additional load of another server in case of emergency.