Riak and host names

Deepak Balasubramanyam deepak.balu at gmail.com
Fri Jan 4 15:47:36 EST 2013


Perhaps I should ask the question differently.

Can someone elaborate on what 'cluster replace' does and how the command is
affected by node names that change after riak starts up ?

Thanks
-Deepak



On Wed, Jan 2, 2013 at 1:13 AM, Deepak Balasubramanyam <
deepak.balu at gmail.com> wrote:

> 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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