How does Dietrich Bonhoeffer's theology relate to salvation by faith alone?

Bonhoeffer was a Lutheran pastor. However, in his book, "*The Cost of discipleship*", he refers to this term called "**cheap grace**", just to give a quote: > Cheap grace is the preaching of forgiveness without requiring > repentance, baptism without church discipline, Communion without > confession, absolution without personal confession. Cheap grace is > grace without discipleship, grace without the cross, grace without > Jesus Christ, living and incarnate. How does this relate to the doctrine of salvation by grace alone, in Lutheranism? There doesn't seem to be any tension between what Bonhoeffer calls "cheap grace" and Martin Luther's "sola fide"?