Transcript services - Indico

Enabling Grids for E-sciencE
AutoSD
Abdeslem DJAOUI
CCLRC-RAL
JRA1 All Hands
CERN, 22-24 Mar 2006
www.eu-egee.org
INFSO-RI-508833
Approaches to Discovery
Enabling Grids for E-sciencE
1. Looking in a well known location
p2p TCP connection
Info Provider
p2p TCP connection
Client
Directory Service
2. Multicasting a request to all available listeners
Service
connectionless multicast
Unicast or Multicast
Service
Client
Service
INFSO-RI-508833
Abdeslem DJAOUI
JRA1 All Hands, CERN, 22-24 Mar 2006
2
Multicasting
Enabling Grids for E-sciencE
• IP multicasting
– One to many communication
 Senders transmit UDP datagram packets to a group address
 Receivers join the group in order to receive the packet
Multiple unicast
IP Multicast
R
S
R
S
R
R
R
R
• IP Multicast group addresses
– Class D address space
 high-order three 3bits are set
 224.0.0.0 ~ 239.255.255.255
– Usage is essentially random – any class D can be used
 Some well known addresses have been registered or reserved
INFSO-RI-508833
Abdeslem DJAOUI
JRA1 All Hands, CERN, 22-24 Mar 2006
3
Automatic Service Discovery What is it?
Enabling Grids for E-sciencE
• Uses techniques such as IP multicasting to
– Automatically announce services instead of manually entering information into a
repository (services announce themselves)
 Services send an announcement to a multicast group when they start or
stop (on a best effort basis)
 Services can announce any change in metadata not just start/stop
• Operational, deployment or security characteristics.
– Services listen to multicast group for client requests
– Clients probe for listening services based on name, type …
• Multicasting relies on existence of IP network only
– No need to know an information service endpoint before discovering
services of interest
– Self announcing services provide up to date information about
themselves
– Discovery without the need to repeatedly poll for information
 Clients listen to the multicast group and discover services as they are
started and when they are stopped (on a best effort basis)
INFSO-RI-508833
Abdeslem DJAOUI
JRA1 All Hands, CERN, 22-24 Mar 2006
4
Example Uses
Enabling Grids for E-sciencE
• Bootstrapping on a LAN
– User connects to a network using a laptop and can find where local
RGMA servers (or UI, or ...) are?
• Bootstrapping should
 Minimize expected client knowledge (near zero configuration)
 Always work (no reliance of client holding volatile data)
• Applications (GUI) can keep the list of its services up to date
dynamically (in automated way)
• Load Balancing
– Adding new resources can be discovered automatically
• Always on Service Discovery even
– When network link to outside is broken
– When Grid Information system breaks down or not known
INFSO-RI-508833
Abdeslem DJAOUI
JRA1 All Hands, CERN, 22-24 Mar 2006
5
AutoSD design
Enabling Grids for E-sciencE
• Target applications not system administrators
– Minimize need to be root or need special for privileges to
advertise or discover services
• Minimize Multicasting across network
– Replies to probes sent Unicast
• Avoid known problems with multicasting
– Minimise flooding problem
 random delay before multicast
• Easily implemented by services, servlets or
applications
• Easily integrated with current SD API
INFSO-RI-508833
Abdeslem DJAOUI
JRA1 All Hands, CERN, 22-24 Mar 2006
6
How about limited multicast
support?
Enabling Grids for E-sciencE
• Multicast is usually blocked across administrative
domains
• A site is usually made of many sub-domains
– Simple broadcast works only in the sub-domain
• Need to join sub-domains
• Relay proxies (services) joins sub-domains into a
simple peer-to-peer network
– Local relay proxy, relays probes to other proxies
– Responds to relayed queries
 Using cached information
 Or may be asked to submit a probe for the most up to date
information
INFSO-RI-508833
Abdeslem DJAOUI
JRA1 All Hands, CERN, 22-24 Mar 2006
7
Summary
Enabling Grids for E-sciencE
• Two aspects of discovery
– Using a well known location
– Multicasting to existing listeners with zero
configuration needs
• AutoSD will initially address user requirements
on BOOTSTRAPPING
• Designed to complement current
SD/Information systems
• A prototype for the simple one sub-domain has
been developed
INFSO-RI-508833
Abdeslem DJAOUI
JRA1 All Hands, CERN, 22-24 Mar 2006
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