← Back to team overview

savanna-all team mailing list archive

Re: Plugin Context object


Hi Jon,

I've updated change request of our implemetation of vanilla Hadoop provider:

Please note that it is draft version and there are a lot of code to improve. Though you can find the main points there.

Just in case I describe tips and tricks to operate with objects inside the plugin:

1. Instances and remote calls.
Instance objects represents actual VMs on OpenStack. Once all instances are provisioned Savanna controller calls configure_cluster() of some plugin and cluster object contains all that instances. Note, all instances are stored inside cirtain node group.
a. You want iterate over all instances to get its hostnames:
def configure_cluster(self, cluster):
        for ng in cluster.node_groups:
                for instance in ng.instances:
                        print instance.hostname

Please refer to available fields and properties of Instance object here:

b. You want to execute some command via ssh on each instance:
def configure_cluster(self, cluster):
        for ng in cluster.node_groups:
                for instance in ng.instances:
retcode, buf instance.remote.excute_command('ls -la')
                        print ret, buf

where ret is returned code and buf is output of the executed command

If you want to copy some data to the some file on the VM you can use:
        data = 'line1\nline2\n'
        instance.remote.write_file_to('/etc/hadoop/config.xml', data)
to read some file
       data = instance.remote.read_file_from('remote_file')

Please see _push_configs_to_nodes() method in plugin.py in my change request(link above).

2. Cluster, NodeGroup and Instnce extra field.
Once your plugin recieves 'cluster' object you can use 'extra' field for any needs. Extra fields will be available in 'cluster' object always. For example you want to remember any object to operate with it directly not iterating over and over all instances. In my plugin implementation I want to remeber NameNode management_ip and hostname to push some configs only to this VM.
cluster.extra['nn_instance'] = None
for node_group in cluster.node_groups:
      ng_proc = node_group.node_processes
      for instance in node_group.instances:
          if 'namenode' in ng_proc:
              cluster.extra['nn_instance'] = instance

#then we can format namenode, for example
cluster.extra['nn_instance'].remote.execute_command("su -c 'hadoop namenode -format' hadoop")

3. Nova
Just import it:
from savanna.utils.openstack import nova

# list of images

# flavors

You can find more nova usages here:

I hope this will help to integrate your provider. Please feel free to ask any questions about invocations and object usage.

Alexander Ignatov

On 6/6/2013 12:07 AM, Jon Maron wrote:

Can the Plugin SPI document (https://wiki.openstack.org/wiki/Savanna/PluggableProvisioning/PluginAPI) be updated with some information regarding the context object and its associated services/APIs? In our implementation we are still interacting directly with nova/ssh etc and we need an understanding of how to migrate those invocations with the context of the savanna server.

-- Jon