[erlang-patches] Running mnesia across a firewall
Serge Aleynikov
saleyn@REDACTED
Thu Mar 6 13:44:02 CET 2008
Ulf Wiger (TN/EAB) wrote:
> Serge Aleynikov skrev:
>> On which node, though? If this is one of the "master" nodes A holding
>> a disk copy of a table X, then the node must have {dist_auto_connect,
>> once} set. If the firewall prohibits inbound access to this node A
>> from some other node C that uses remote mnesia interface to access
>> table X, then the only way to establish connection to node C is to do
>> on node A net_kernel:connect(C). However if that connection drops,
>> there's no way to reestablish that connection without restarting node
>> A. Remember that in case of {dist_auto_connect, once} net_kernel
>> checks if a connection is barred and if it is it won't allow to
>> connect to a node that previously was connected.
>
> Correction 1: It's net_kernel:connect_node(Node). My bad.
>
> Correction 2: net_kernel:connect_node/1 ignores the value of
> dist_auto_connect
>
> What we've done is to keep a "maintenance channel" (not distr Erlang),
> over which we can negotiate which node should restart.
It turned out that was making the same mistake by using
net_kernel:connect(Node) rather than net_kernel:connect_node(Node).
Quite easy to get confused as two functions have the same signature. :-(
Thanks for pointing this out!
So for making mnesia work across a firewall a combination of kernel
options including global_groups as well as user-level
pinging/starting/stopping remote mnesia is sufficient.
Serge
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