[erlang-questions] net_kernel:start/1 and net_kernel:connect_node/1 errors

[Éric Pailleau]

Hi, 

Did you check that both have same cookie ?

"Envoyé depuis mon mobile " Eric

---- Khitai Pang a écrit ----

>Hi,
>
>I'm having some problems with distributed erlang on Linux.
>
>I have two ubuntu hosts, and on each node the ERL_EPMD_PORT environment 
>variable is set to 5779.
>
>Hostnames are properly set in /etc/hosts on both hosts.  Erlang is 
>started on the two hosts by
>
>$ erl -sname er1@REDACTED
>
>(er1@REDACTED)1> node().
>er1@REDACTED
>
>$ erl -sname er2@REDACTED
>
>(er2@REDACTED)1> node().
>er2@REDACTED
>
>and epmd is running on both hosts listening on 5779.
>
>
>Question 1:  Why does connecting to er2@REDACTED using 
>net_kernel:connect_node/1 fail?
>
>(er1@REDACTED)4> net_kernel:connect_node(er2@REDACTED).
>false
>
>It runs for a couple seconds and returns false.
>
>Is it because epmd is not listening on the default port?
>
>
>Question 2: If epmd is not running, when I run 
>net_kernel:start([er1@REDACTED, shortnames]), it returns error.  Why? If 
>it's caused by epmd not running, how to make sure that epmd is started 
>when you start an OTP release?
>
>1> net_kernel:start([er1@REDACTED, shortnames]).
>{error,
>     {{shutdown,
>{failed_to_start_child,net_kernel,{'EXIT',nodistribution}}},
>      {child,undefined,net_sup_dynamic,
>          {erl_distribution,start_link,[[er1@REDACTED,shortnames]]},
>          permanent,1000,supervisor,
>          [erl_distribution]}}}
>
>
>Question 3: After starting erl with -sname, if you run netstat, you'll 
>see a process listening on a random port, what is it?
>
>tcp        0      0 0.0.0.0:23333           0.0.0.0:* LISTEN      
>12650/beam.smp
>
>
>Question 4: If an OTP release is meant to run on multiple nodes, how to 
>properly set node name and start distribution on each node 
>automatically?  I want to start running the release on all nodes by 
>running one command on one of the nodes.
>
>Currently I'm planning to do it this way:
>
>1) hardcode all participating hostnames in sys.conf, something like 
>[{"er1", "host1"}, {"er2", "host2"}]
>2) on each host, when the erlang application starts, it reads the config 
>from sys.conf, finds its own name and use net_kernel:start/1 to set the 
>node name and start distribution
>
>What is the best practice to do it?
>
>
>Thanks
>Khitai
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