CloudFront-Viewer-Postal-Code does not work in Vietnam country

CloudFront uses Maxmind database to update geo specific information. This data is refreshed on a weekly basis, however, will take up to five weeks to propagate across the worldwide fleet in a phased approach. This slow rollout is intentional to limit the potential impact of a negatively impacting deployment or geolocation dataset.

If Geo database installed in CloudFront edge location did not have geo information like Longitude, Latitude or Postal Code, CloudFront will not forward such information to origin though cache policy or origin request policy through headers like:

CloudFront-Viewer-Postal-Code, CloudFront-Viewer-Longitude, CloudFront-Viewer-Latitude

Therefore, if the request is made using an IP address that might have been updated in Maxmind databases within the last 5-6 weeks you don't see the 'CloudFront-Viewer-Postal-Code' header for these requests and you would be able to see them updated in 5-6 week time.

Thus, the CloudFront team suggest to send requests from different client IP addresses if you need to test CloudFront-Viewer header with your application.

[+] GeoRestriction - https://docs.aws.amazon.com/cloudfront/latest/APIReference/API_GeoRestriction.html