I have started receiving errors from the Phabricator S3 file engine when uploading to S3. This happens at both the /file endpoint and when creating diffs, pasting files, etc. The error states:
PhabricatorS3FileStorageEngine: S3Exception: S3::putObject():  SSL peer certificate or SSH remote key was not OK
This is running on an Ubuntu instance on EC2. Aside from Ubuntu security updates nothing has changed on this box. All S3 related commands fail.
I have tried curl'ing to various S3 URLs from the box (as ubuntu/root/www-data) and do not receive certificate errors.
Any thoughts on how to debug this or fix the issue would be greatly appreciated.