Node Services Development

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Node ServicesDevelopment

• Thomas D. Uram
• turam_at_mcs.anl.gov
• Argonne National Laboratory

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Access Grid Architecture
VenueServer

• VenueServer
• Server component for Venues
• Venue
• Virtual representation of a meeting room
• VenueClient
• User software for entering a Venue
• Node
• Aggregation of hardware and software for
  participating in a meeting

Venue
Venue
Venue
Venue Client
Node
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Node Architecture
Node

• NodeService
• Aggregates ServiceManagers
• Manages node configurations
• ServiceManager
• Exposes available machine resources
• Manages AGServices
• AGService
• Interface for controlling access to machine
  resources
• Exposes service configuration interface

Node Service
Service Manager
AGService
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Overview

• Expose machine resources
• Describe available resources (e.g. video card)
• Provide configuration layer
• Describe available configuration parameters (e.g.
  video quality level)
• Accept configuration of those parameters
• Provide service abstraction
• Services are controlled over SOAP interface, so
  could be written in any language with an
  interoperable SOAP implementation

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Operation

• Resources
• Resources represent something the machine can
  make available (e.g. video capture device)
• Resources are currently defined with only type
  and role attributes (e.g. typevideo,
  roleproducer)
• When a service is added, it may have a resource
  assigned to it

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Operation
Venue
Client Profile (incl. Capabilities)

• Service Capabilities
• The capabilities of the node are collected and
  passed to the venue
• Capabilities are currently defined with only type
  and role attributes (e.g. typevideo,
  roleproducer)

Venue Client
Capabilities (aggregated from services)
Node
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Operation
Venue State (incl. StreamDescs)
Venue
Client Profile (incl. Capabilities)

• Capabilities Negotiation
• The capabilities of the node are collected and
  passed to the venue
• The venue allocates a stream (multicast group)
  for each producer capability of a yet
  non-existent type
• The venue returns a stream (multicast group) for
  each existing consumer capability type
• The returned streams are passed down to the
  services

Venue Client
Capabilities (aggregated from services)
Node
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Operation
Venue State (incl. StreamDescs)
Venue
Client Profile (incl. Capabilities)

• Stream Descriptions
• The venue returns a stream description (multicast
  group) for each existing consumer capability type
• The returned stream descriptions are passed down
  to the services
• Service configure for the given streams
  (typically passing the contained multicast groups
  to media tools)

Venue Client
StreamDescriptions
Capabilities (aggregated from services)
Node
Update AGServices
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Configuration

• Services may have a set of configurable
  parameters that control their operation
• For example video quality level, audio input
  gain
• Configuration parameters are defined in terms of
  types from AGParameter.py
• ValueParameter
• TextParameter
• OptionSetParameter
• RangeParameter
• Basic handling of parameters is performed in
  AGService

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Configuration

• The Node Management user interface includes code
  to represent parameters for editing

TextParameter

OptionSetParameter

RangeParameter
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Configuration

• Parameter values can be used when the service is
  started
• Configuration data is persisted in saved node
  configuration files
• ConfigParser format
• Stored in AccessGrid/nodeConfig

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Other

• Logging
• Services derived from AGService automatically
  create a logfile in AccessGrid/Logs, based on
  Service class name

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Packaging

• A service is delivered in a service package, a
  zip-file containing the Python implementation, a
  service description file, and any supporting
  implementation files
• A service description file (.svc) contains
  information presented to the user before adding
  the service
• Service packages are installed using agpm.py
  (similar to shared applications)
• agpm.py -z ServicePackage.zip
• Service packages are extracted to a temporary
  directory, subject to their version

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Packaging

• Sample service description file

ServiceDescription name DebugService descripti
on Example Debug Service capabilities
Capability1 Capability2 Capability3 executable
DebugService.py platform neutral version
1.0 Capability1 role consumer type
audio Capability2 role consumer type
video Capability3 role producer type debug
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AGService API
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AGService API

• AGServices are typically exposed using the
  AGServiceIW interface, but can specialize it to
  their needs

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Calls from Toolkit

• On Enter
• GetCapabilities()
• Called during aggregation of capabilities from
  AGServices
• ConfigureStream(StreamDescription)
• Called to set the stream the AGService should use
• Ignores trivial stream changes
• On Exit
• Stop()
• Called to stop the AGService
• Other
• Start()
• Not called explicitly
• Typically called from ConfigureStream

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Example DebugService

• Basic service that
• logs messages in response to various calls to it
• defines debug parameter which can be set through
  configuration interface
• Review log file (DebugService.log) for proper
  operation

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Exercise ClientAnnouncerService

• Service to announce presence
• Sends users name over a multicast group
• Watch for your name to appear on the ClientViewer

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Exercise ClientAnnouncerService

• Retrieve Venue URL from VenueClient
• Send Venue URL with name
• Use fixed multicast address, to share presence
  data across Venues