I've tried to install docker cloud several months ago but I removed it. Now I have updated to Debian Stretch from Jessie and I get this error when I update via "apt-get update" and don't know how to solve it. Can anyone offer some help? Thanks!
sudo apt-get update
Get:1 http://debian.mirrors.ovh.net/debian stretch-updates InRelease
Ign:2 http://debian.mirrors.ovh.net/debian stretch InRelease
Get:3 http://repo.cloud.docker.com/ubuntu dockercloud InRelease [1,383 B]
Get:4 http://debian.mirrors.ovh.net/debian stretch Release
Hit:5 https://deb.nodesource.com/node_6.x jessie InRelease
Hit:6 https://apt.dockerproject.org/repo debian-stretch InRelease
Hit:7 http://security.debian.org stretch/updates InRelease
Ign:8 http://download.draios.com/stable/deb stable-amd64/ InRelease
Hit:9 http://download.draios.com/stable/deb stable-amd64/ Release
Ign:3 http://repo.cloud.docker.com/ubuntu dockercloud InRelease
Fetched 203 kB in 0s (247 kB/s)
Reading package lists... Done
W: GPG error: http://repo.cloud.docker.com/ubuntu dockercloud InRelease: The following signatures were invalid: 278FE7333CFF7F8B60B677E85DD27147EF170D1C
W: The repository 'http://repo.cloud.docker.com/ubuntu dockercloud InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://repo.cloud.docker.com/ubuntu dockercloud InRelease: The following signatures were invalid: 278FE7333CFF7F8B60B677E85DD27147EF170D1C
W: The repository 'http://repo.cloud.docker.com/ubuntu dockercloud InRelease' is not signed.
Actually this is a Warning not an Error. It seems that somewhere in Your SourcesList(e.g. /etc/apt/sources.list) You still have a docker repo.
$ sudo grep -w "docker.com" /etc/apt/*.*
will show where is docker's url. If You do not need it any more, just comment this line.
Well, if You still need docker this link could be helpful.