Packages of GlusterFS 3.7 for Debian stretch are available here from the Gluster Community...

Add the GPG key to apt:

    wget -O - http://download.gluster.org/pub/gluster/glusterfs/3.7/LATEST/Debian/stretch/pub.key | apt-key add -

N.B. the pubkey for Debian stretch has changed. Stretch dpkgs are signed with the same key as the Fedora, RHEL, and CentOS packages

Add the source:

    echo deb http://download.gluster.org/pub/gluster/glusterfs/3.7/LATEST/Debian/stretch/apt stretch main > /etc/apt/sources.list.d/gluster.list 

Update package list:

    apt-get update

Install:

    apt-get install [ glusterfs-server | glusterfs-client ]

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Packages from the Debian project are available in the unstable distribution:

    http://packages.debian.org/search?keywords=glusterfs&searchon=names&suite=unstable&section=all