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anchortop
Geronimo Clustering Overview - 10,000 feet...
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This document will begin the task of :
- enumerating clustering requirements in Geronimo's tiers
- abstracting out commonality from these
- cataloguing software available to us that may be used to implement them
- suggesting a clustering architecture
A 'Cluster' is an architecture that achieves scalability and high availability through the arrangement of multiple smaller, cheaper, less reliable, resources, rather than single large, expensive, extremely reliable ones.
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We will enumerate and examine these usecases.
Web
URL: http://java.sun.com/products/servlet/download.html#specs
Interest Group: Jules Gosnell, Jan Bartel, Jeff Genender, David Jencks,...
Clustering in the web-tier has two points of implementation :
The HTTP Load Balancer:
- our solution should work with any load-balancer
- we can expect the LB to support some form of affinity (sticky or persistant sessions).
The HttpSession:
- large numbers of potentially large objects (more data in the tier than can comfortably be held in one node) - needs partitioned cache
- typically frequently written
- typically frequently read
- typically a single consumer/client
- transactionless
- only one copy of an HttpSession may be 'active' at any one time
- multi-threaded
- pessimistic
- suggested impl - WADI
N.B.: Some other solutions allow the clustering of more than just the HttpSession. The spec only requires that data stored in the HttpSession is distributable.
Dev Threads
WADI and Network Partitions: http://www.mail-archive.com/dev%40geronimo.apache.org/msg15855.html
WADI/AS merger - http://www.mail-archive.com/dev@geronimo.apache.org/msg14749.html
EJB
URL: http://java.sun.com/products/ejb/docs.html#specs
Interest group: David Blevins, Gianny Damour
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The Client/Proxy (equiv to Web Load-balancer):
- cluster-aware proxies needed
- can same proxies work with both OpenEJB and IIOP protocols ?
The Server:
MDB
- stateless
SLSB
- stateless
SFSB
- large numbers of potentially large objects (more data in the tier than can comfortably be held in one node) - needs partitioned cache
- transactional
- typically frequently written
- typically a single consumer/client
- typically frequently read
- single threaded
- pessimistic
- suggested impl - WADI
Entity
- potentially multiple consumers
- mapped to shared, persistant store
- transactional
- read/write frequency variable, pluggable impls required (e.g. RO Beans etc..)
- distributed db backed cache needed
- since mapped to db, does not need partitioned cache, data can just be unloaded
- distributed caching of entity beans: http://www.mail-archive.com/dev%40geronimo.apache.org/msg15697.html
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- suggested impl - ActiveSpace
Dev Threads:
client stubs and load-balancing: http://www.mail-archive.com/dev@geronimo.apache.org/msg13533.html
AC in client stub: http://www.mail-archive.com/dev@geronimo.apache.org/msg14756.html
Entity invalidation...
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Interest Group: Rajith Attapattu http://java.sun.com/products/jndi/1.2/javadoc/
Apache Directory - http://directory.apache.org/ (may use this?)
- small amounts of small objects
- typically seldom written
- typically frequently read
- typically multiple consumers/clients
- multi-threaded
- transactionless
- prime candidate for straight forward 1->all replication
- suggested impl - ActiveSpace
Dev Threads:
ActiveSpace in JNDI: http://www.mail-archive.com/dev@geronimo.apache.org/msg14743.html
WADI/AS merger - http://www.mail-archive.com/dev@geronimo.apache.org/msg14749.html
JMS
http://java.sun.com/products/jms/docs.html
- impl - ActiveMQ
The ActiveMQ team will happily look after the clustering of JMS. For more information see the current Clustering Support in ActiveMQ
Dev Threads:
AMQ Clustering: http://www.mail-archive.com/dev%40geronimo.apache.org/msg15717.html
Deployment
http://jcp.org/en/jsr/detail?id=088
- potentially large objects (perhaps we could just send references)
- union of tier content smaller than single node capacity
- seldom written (undeployed)
- frequently read (invoked)
- transactionless
- no uniqueness constraint ? (what should we do about creating heterogeneous deployments?)
- prime candidate for straight forward 1->all replication
- suggested impl - ActiveSpace
suggestion - 'deployments sets' - a groups of nodes that share/implement a homogeneous deployment. See "Homogeneous vs Heterogeneous Deployments" section.
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suggestion - could replication be done synchronously and serially, so that as the app is deployed on each node it can be sanity checked before the distribution continues to the next node ?
WADI,AC,AS & Deployment: http://www.mail-archive.com/dev@geronimo.apache.org/msg15214.html
Management/Monitoring
http://jcp.org/en/jsr/detail?id=077
- still little discussion here
- may need to be centralised
- history - perhaps selected statistics snapshots should be dropped
into JMS every few secs by each server, then stashed in an rrdb ?
(WHEN, WHERE, WHAT, VALUE)
POJO
JCache - http://jcp.org/en/jsr/detail?id=107
- all of the above - whatever is available to Geronimo should be available to application-space pojos.
- JCache, and related technologies...
- suggested impls - ActiveSpace/WADI
DB
any takers ?
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Network Partitions: check out 'Totem' thread on dev - not yet archived...
Application Session: http://www.mail-archive.com/dev@geronimo.apache.org/msg12072.html
clustering shopping list: http://www.mail-archive.com/dev@geronimo.apache.org/msg10561.html
Web Services
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Clustering Substrate
- suggested impl - ActiveCluster on top of various protocols
Auto-wiring
- clients need to autolocate nodes (ejb-client->jndi-port, http-load-balancer->http=port etc...)...
- nodes on same box need to negotiate ownership of per-host resources (e.g. ports)
Homogeneous vs Heterogeneous deployments
- homogeneous cluster is one set of nodes - the universal set
- heterogeneous cluster is one set (the universal set), with subsets defining internal scopes
Perhaps ActiveCluster could be extended to allow subclusters via the
same Cluster connection, or we could use multiple cluster
connections, or an AMQ MessageGroups...?
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Suggested Building Blocks
ActiveMQ
URL: http://incubator.apache.org/activemq/
Interest Group: James Strachan, Hiram Chirino, ...
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ActiveCluster
URL: http://activecluster.codehaus.org/
Interest Group: James Strachan, Hiram Chirino, ...
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ActiveSpace
URL: http://activespace.codehaus.org/
Interest Group: James Strachan, Hiram Chirino, ...
Provides two abstractions, a JCache style Cache (replicated and/or transactional) and a JavaSpaces style Space, for distributed computing.
WADI
URL: http://wadi.codehaus.org/
Interest Group: Jules Gosnell,...
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Tomcat Clustering
URL: http://tomcat.apache.org/tomcat-5.0-doc/cluster-howto.html
Interest Group: Jeff Genender, ...
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EVS4J/TOTEM
URL: http://www.bway.net/~lichtner/evs4j.html
Interest Group: Guglielmo Lichtner
Extended Virtual Synchrony for Java.
Potentially very useful in cases where we need fast, strictly ordered 1->all messaging.
Might be integrated via ActiveCluster or ActiveMQ
Introduction: http://www.mail-archive.com/dev%40geronimo.apache.org/msg15644.html
Totem and ActiveCluster: http://www.mail-archive.com/dev%40geronimo.apache.org/msg15695.html
Infiniband: http://www.mail-archive.com/dev%40geronimo.apache.org/msg15743.html
Further Discussion
Further Reading
http://portal.acm.org/citation.cfm?id=326136http://scholar.google.com/url?sa=U&q=http://historical.ncstrl.org/tr/ps/cornellcs/TR99-1726.pshttp://www.jgroups.org/javagroupsnew/docs/index.htmlhttp://citeseer.csail.mit.edu/amir95totem.htmlhttp://docs.codehaus.org/display/WADI/Libraryhttp://citeseer.ist.psu.edu/32449.html
"Fault Tolerance in Distributed Systems"
Pankaj Jalote, 1994
Chapter 7, Section 5, "Degree of Replication"