[erlang-questions] Masterless application design

Cristian Hancila <>
Sun Nov 11 00:08:52 CET 2012


Hello Erlangers,

I'm fairly new to Erlang and I'm trying to brainstorm an architecture for
an ideally masterless system, mainly how to achieve it on top of Erlang and
OTP. The main components are 1..n nodes as public web based authentication
services  and 1..n nodes as the ultimate hosts of the client, over a long
lived tcp connection.  The web service nodes do registration and
authentication, and decide which host the client will connect to. The
authentication nodes need to be aware of all host nodes, and need to
realize when new host nodes get added. The host nodes provide a
notification mechanism for usage statistics, and each auth node registers
for this notification in order to figure out some heuristics on deciding
where to forward a client when they want to connect.

My main issue is with figuring out if when a new node joins the cluster,
does it/will it run the host_service application? If I can't make that
guarantee then I would need to periodically scan all nodes an see if
host_service is running on them. This seems like a bad design. Is there an
OTP or standardized erlang pattern to achieve this?

Right now the only idea I came up with is having an application running on
all my nodes that specify the "feature" of the node, so when a node joins
the cluster, the web service app checks the capabilities of the node, and
either ignores or it grabs the host_service process, or if the host_service
happens to be dead periodically checks until it's alive.

Lastly I'm also debating if this complexity is worth the effort, it seems
that using a global process as a host_service registry would be much easier.

Thanks for any advice, and also keep in mind this is mostly a personal
academic exercises in building distributed systems and learning Erlang.
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