Riak and host names

Matt Black matt.black at jbadigital.com
Mon Jan 7 17:00:45 EST 2013


Thanks for this Charlie.

I'm running a production Riak cluster on AWS which runs constantly, and
I've been wondering how I might be able to easliy stop and start AWS nodes
for a testing and benchmarking cluster (to save on cost).

By using the 'riaknode1.priv' hostname method you describe, would I be able
to stop and then restart a whole cluster of nodes at once? (As described by
Deepak, AWS assigns new IPs when a VM starts).

Thanks
Matt


On 8 January 2013 01:31, Charlie Voiselle <cvoiselle at basho.com> wrote:

> Deepak:
>
> When you name a node in app.config with -name it has to have a '.' in it,
> like riak at hostname.net  As you have surmised, you can get around that if
> you use the -sname argument instead.
>
> They have to be done consistently.  In your example, had you used the
> -sname argument, `riak at riaknode1` would work.  Making a host entry
> `riaknode1.priv` that points to the local address would work with the -name
> argument.
>
> The inportant thing about -name and -sname is that they can't mix within a
> cluster.
>
> Cluster replace is designed to replace a node with a new one and transfer
> all the partitions. You can cheat and use it to rename a node though.
>
> The process to do this would look like the following:
>
>    - Stop the node to rename with `riak stop`
>    - Mark it 'down' *from another node in the cluster *using `riak-admin
>    down «old nodename».
>    - Rename the node in vm.args.
>    - Delete the ring directory.
>    - Start the node with `riak start`.
>    - It will come up as a single instance which you can verify with
>    `riak-admin member-status`.
>    - Join the node to the cluster with `riak-admin cluster join «cluster
>    nodename» `
>    - Set it to replace the old instance of itself with `riak-admin
>    cluster replace «old nodename» «new nodename»
>    - Plan the changes with `riak-admin cluster plan`
>    - Commit the changes with `riak-admin cluster commit`
>
>
> As you can see, this is a very large effort, so best to use hostnames that
> aren't moving around.  Apologies for you getting this twice, Deepak. I
> failed to reply to the list as well.
>
> Hope this makes sense...
> Charlie
> On Jan 1, 2013, at 2:43 PM, 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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