Downloading http://cdn-fastly.deb.debian.org/debian/dists/stretch/InRelease...
Downloading http://cdn-fastly.deb.debian.org/debian/dists/stretch/Release...
Downloading http://cdn-fastly.deb.debian.org/debian/dists/stretch/Release.gpg...

gpgv:  RSA key ID 2B90D010

gpgv:  RSA key ID B7D453EC

gpgv:  RSA key ID 1A7B6500

ERROR: unable to fetch mirror: verification of detached signature failed: exit status 2