It depends -
If you have left our former state of residency, have no ties to this former state and will not be returning to your former state of residency, then you can use "foreign or US possession" as your state for 2017.
If you intent to return to your former state of residence when you return, then that state will remain your resident state during your time overseas.
Also, if you are outside the US on the first due date (April 16th, 2018), you will receive an automatic extension under June 15th, 2018. Just make sure to check this election if filing affect April 16th but before June 15th.
