Riak and host names

Deepak Balasubramanyam deepak.balu at gmail.com
Tue Jan 1 14:43:02 EST 2013


I took the AWS EC2 riak image for a spin today. I have a query regarding
riak nodes and how they behave when the machine reboots.

When an EC2 instance reboots, the internal ip / internal DNS / external DNS
change. This renders the app.config and -name argument on vm.args
incorrect. I was exploring solutions to deal with this problem.

*1. Preventive measures*

Someone on this thread dated May
2011<http://riak-users.197444.n3.nabble.com/EC2-and-node-names-td2892047.html>
suggested
using host file entries that point to the local internal IP address. That
does not seem to work. Riak fails with the following error when I add a new
entry to /etc/hosts and configure vm.args with -name riak at riaknode1

Hostname riaknode1 is illegal

I confirmed that riaknode1 pings correctly before starting riak. I guess
erlang tries to match the hostname of the system resulting in this failure
? Can anyone throw some light on this ?

*2. Use -sname*

Is starting the erlang VM with the sname flag an option if it will help
prevent the 'illegal hostname' error ?
Disclaimer: My knowledge of erlang is close to zilch, so sorry if that
option sounded like something you could dismiss easily :)

*3. Use cluster replace
*

a. I understand that the IPs in app.config and vm.args can be replaced with
the correct IP on a restart and using a subsequent 'cluster replace'
command will do. Will executing the 'cluster plan' and 'cluster commit'
commands now produce network chatter ?

b . What happens if 2 nodes go down and one was joined with the other. They
both have 2 different IP addresses on restart. How will 'cluster replace'
work now ?

Do let me know your thoughts.

Thanks
-Deepak
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