We changed the internal signing key on the following repositories :

http://last.public.ovh.hdaas.snap.mirrors.ovh.net/debian/
http://last.public.ovh.hdaas.snap.mirrors.ovh.net/ubuntu/

Therefore, you might experience the following error during an apt update :

W: GPG error: http://last.public.ovh.hdaas.snap.mirrors.ovh.net/debian jessie Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DC286CCC60B23E2F
E: The repository 'http://last.public.ovh.hdaas.snap.mirrors.ovh.net/debian jessie Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

To add the new key on your server, please issue this command :

# wget -qO - http://last.public.ovh.hdaas.snap.mirrors.ovh.net/debian/archive.key | apt-key add -
# apt update