You must follow your local people and observe the day of arafah and eid according to the authorized local Islamic authorities, regardless of Saudi Arabia. 

I live in Hongkong and the 9th day of Dhul hijjah (Arafah) will be on 21~8~2018 here In sha Allah but on the same date Saudi Arabia will be celebrating Eid. I know Muslims are not allowed to fast on the day of Eid. So whom should I follow saudi Arabia or Hk time table ? I’m confuse how can be the day of arafah be different.