This is more appropriate in the actual version (0.12.X)
The supported operators are:
Equality: == and !=
Numerical comparison: >, <, >=, <=
Boolean logic: &&, ||, unary !
https://www.terraform.io/docs/configuration/interpolation.html#conditionals
condition_one and condition two:
count = var.condition_one && var.condition_two ? 1 : 0
condition_one and NOT condition_two:
count = var.condition_one && !var.condition_two ? 1 : 0
condition_one OR condition_two:
count = var.condition_one || var.condition_two ? 1 : 0