Études for Erlang

Étude 11-3: Independent Server and Client

In the previous études, the client and server have been running in the same shell. In this étude, you will make the server available to clients running in other shells.

To make a node available to other nodes, you need to name the node by using the -name option when starting erl. It looks like this:

michele@localhost $ erl -name serverNode
Erlang R15B02 (erts-5.9.2) [source] [smp:2:2] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.9.2  (abort with ^G)
([e-mail])1>

This is a long name. You can also set up a node with a short name by using the -sname option:

michele@localhost $ erl -sname serverNode
Erlang R15B02 (erts-5.9.2) [source] [smp:2:2] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.9.2  (abort with ^G)
(serverNode@localhost)1>

Warning

If you set up a node in this way, any other node can connect to it and do any shell commands at all. In order to prevent this, you may use the -setcookie Cookie when starting erl. Then, only nodes that have the same Cookie (which is an atom) can connect to your node.

To connect to a node, use the net_adm:ping/1 function, and give it the name of the server you want to connect to as its argument. If you connect succesfully, the function will return the atom pong; otherwise, it will return pang.

Here is an example. First, start a shell with a (very bad) secret cookie:

michele@localhost $ erl -sname serverNode -setcookie chocolateChip
Erlang R15B02 (erts-5.9.2) [source] ...