Service discovery: should we use SLP?

Stephen Gallagher sgallagh at redhat.com
Fri Jun 21 15:58:14 UTC 2013


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On 06/21/2013 11:00 AM, Tomáš Smetana wrote:
> Hello, I have mentioned this several times before: I had been
> asked to provide some example scripts that would "for every
> computer on the network... do something".  It's not quite obvious
> how to actually find every WBEM-capable device on the network.
> 
> There are several ways how to do that and it seems like SLP is
> being used in combination with WBEM quite often. Maybe it is the
> right thing for us to use for the OpenLMI discovery as well. The
> Pegasus CIMOM can register itself in the local SLP server and then
> even advertises the registered profiles as the service attributes.
> Here's the sample output from my testing machine for the
> illustration:
> 
> [tsmetana at zaphod ~]$ slptool -u f-19-local findsrvs service:wbem 
> service:wbem:https://[fe80::5054:ff:feb6:b32]:5989,65025 
> service:wbem:https://192.168.122.12:5989,65025 [tsmetana at zaphod
> ~]$ slptool -u f-19-local findattrs service:wbem 
> (template-url-syntax=https://192.168.122.12:5989),(service-id=PG:192-168-122-12),(service-hi-name=Pegasus),(service-hi-description=Pegasus
>
> 
OpenPegasus Version 2.12.1
> Development),(template-type=wbem),(template-version=1.0),(template-description=This
>
> 
template describes the attributes used for advertising Pegasus CIM
> Servers.),(InteropSchemaNamespace=root/PG_InterOp),(FunctionalProfilesSupported=Basic
>
> 
Read,Basic Write,Schema Manipulation,Instance
> Manipulation,Association Traversal,Query Execution,Qualifier 
> Declaration,Indications),(MultipleOperationsSupported=FALSE),(AuthenticationMechanismsSupported=Basic),(AuthenticationMechanismDescriptions=Basic),(CommunicationMechanism=CIM-XML),(ProtocolVersion=1.0),(Namespace=root/PG_InterOp,root/PG_Internal,root/cimv2,root),(RegisteredProfilesSupported=SNIA:Server,DMTF:Profile
>
> 
Registration,SNIA:Server:Indication,SNIA:Profile
> Registration,SNIA:Server:Software,SNIA:SMI-S)
> 
> SLP would bring another dependency (the slpd daemon) but has some 
> advantages: the discovery queries are multicasted, Pegasus already 
> supports this out-of-the-box (we only need to start registering 
> profiles properly) and it looks to be quite simple.
> 
> While playing with the SLP tools in Fedora I have written Python 
> bindings for OpenSLP, so we should be able to integrate SLP
> support in the LMI shell: https://github.com/tsmetana/pyslp (We
> can "openlmify" the sources and integrate in our code eventually.)
> 
> Opinions?
> 



What downsides do you see with SLP other than the added dependency? It
sounds to me to be almost to good to be true (already supported by
Pegasus, etc.) so I would like to know what the counter-arguments
might be.
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