Being a USA citizen living abroad or Permanent Resident ie Green card holder comes with obligations to report and pay US taxes. As a US Citizens or Permanent Resident you are taxed on your world income. Though you may be eligible for exclusions of some earned income subject to tax and or credits for taxes paid in foreign countries, this may depend on nature of your stay in the foreign country, tax treaties between your country of residence and The USA.
Nexus caters to numerous expatriate clients. We keep ourselves updated with the changing legal and reporting requirements including FBAR forms, Form 2555 etc.