inet_ssh_dist

inet_ssh_dist is an Erlang distribution (network protocol) that runs over ssh.

Configuration could be as simple as,

-proto_dist inet_ssh

and then everything goes over ssh. Even epmd.

• No you don't need a special SSH server.
• No you don't need the Erlang SSH server (and in fact, this isn't even supported yet)

An ssh known_hosts must already be populated since the distribution will refuse to accept new hosts on an ad-hoc basis.

Using as a road-warrior

If your Erlang cluster is already using inet_dist_tcp and you can ssh to your nodes, then you don't have to do anything except use -proto_dist inet_ssh on your road-warrior machine, and tell Erlang what your node username is, e.g.

-proto_dist inet_ssh -ssh_default_user erlang

Using for cluster-communication

Note this isn't very fast, but if you can't get IPSEC working this is a lot easier than getting TLS working right.

Creating a user for restricted port forwarding

First, make sure you know what port Erlang is going to use, by adding the following to the command line:

-ssh_default_user erlang
-inet_dist_listen_min 10069
-inet_dist_listen_max 10069

Edit /etc/ssh/sshd/config:

Match User erlang
  AllowTcpForwarding local
  X11Forwarding no
  PermitTunnel no
  PermitTTY no
  GatewayPorts no
  AllowAgentForwarding no
  AllowStreamLocalForwarding no
  PermitOpen localhost:10069
  ForceCommand echo 'This is a restricted account'

Reload sshd. Then create the user:

sudo useradd -m erlang

You can add keys manually (but not using ssh-copy-id).

Adding an SSH key that can only be used for Erlang

If you don't have root, or you share your application user with your release team (ha ha ha enterprise), then you will want to add the ssh key directly to the user account.

First, make sure you know what port Erlang is going to use, by adding the following to the command line:

-ssh_default_user erlang
-inet_dist_listen_min 10069
-inet_dist_listen_max 10069

Then add to the beginning of every restricted key in your ~/.ssh/authorized_keys file:

command="echo 'This is a restricted account'",no-agent-forwarding,no-X11-forwarding,permitopen="localhost:10069"

Here's a complete example, but obviously use your own key:

command="echo 'This is a restricted account'",no-agent-forwarding,no-X11-forwarding,permitopen="localhost:10069" ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAQEAqrlwlnH3xpHntabqfgGBrMOPc83ShDCzTNskx+wQ30sScsONjikuyKQ0FV34RDGhSsd3VpNE8hUpYTVPPCI0wDgOZrUSKWGSbN9s6q1OOcaKRnuOxBguFdgimDemFuQ3VFj1hzZ0ZHt9tq442AQjpDdxHb8KBiiu/qziTvPVP0hzO7xty3ebBxxuRn7vSnKqswM8PQOqJXksok38PoxTDL2l9Nuz5vhl6gS8KA7szlGpve+EnYNgr9ob0QEm5TqKFbYwpaSuOCEQivc/m3urNUIis80sHP/PWFVK4sPc48cpvn6Tzosx+GK5j2KMynJVOES4Hc8LyRWysssBFQyZhw== rsa-key-20000000

Verifying you've got a restricted SSH setup

First, make sure what doesn't work:

ssh erlang@host #connection should be closed
ssh erlang@host /bin/date #connection should be closed and date is not executed
ssh -N -D 10069 erlang@host #wrong forwarding type
ssh -N -L 8080:127.0.0.1:80 erlang@host #wrong port number
sftp erlang@host #wrong subsystem

then verify what works:

ssh -N -L 1234:localhost:10069 erlang@host