The document discusses Sling replication, including: 1) Sling replication was contributed to Sling in November 2013 and aims to be simple, resilient, and fast. 2) Replication is achieved through replication agents that export and import replication packages between Sling instances. 3) Replication packages are serialized and sent between instances, with various queue providers and distribution strategies available. 4) Configurations define the exporter, importer, queue provider, and distribution strategy for each replication agent.

1. APACHE SLING & FRIENDS TECH MEETUP
BERLIN, 22-24 S EPTEMBER 2014
Data replication in Sling
Tommaso Teofili, Adobe Systems

2. Use cases
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3. Replication in AEM
§ Moving authored content to publish servers
author
publish
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4. Replication in AEM
§ Moving user generated content back to
author for moderation
author
publish
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5. Replication in AEM
§ Moving user generated content to other
publish instances
author
publish
publish
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6. Replication module should ...
§ transfer resources between Sling instances
§ push from server A to server B
§ pull from server C to server D
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7. Example: replication of /foo/bar
§ HTTP request for pushing /foo/bar
§ Resources get
§ packaged
§ sent
§ received
§ persisted
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8. we’re not in 1999 ... anymore
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9. NRT sync on N servers
publish1
publish2
author1
author2
publish3
publish4
publish5
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10. Oak instances served by same MongoDB
publish1
author
publish2
oak
oak
mongo
mongo
mongo
mongo
p1
or
p2
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11. Cloud based infrastructures
P1
to
pN
publish1
author1
author2
publish2
publish3
publish4
publish4
publish4
publish4
publish4
publishN
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12. Overview
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13. Sling Replication
§ Contributed to Sling in November 2013
§ First release ?
§ Main goals
§ Simple
§ Resilient
§ Fast
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14. Replication agents
§ Execute replication requests by:
§ exporting replication packages from a (remote)
Sling instance
§ importing replication packages into a (remote)
Sling instance
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15. Replication agents
§ A “push” agent has
§ A “local” exporter
§ Creating a package locally for the resources to be
replicated (e.g. from the underlying JCR repo)
§ A “remote” importer
§ Importing the exported package remotely by sending
it to a designated endpoint to persist it
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16. Replication agents
§ A “pull” agent has
§ A “remote” exporter
§ Pulling a package from a remote Sling instance
designated endpoint
§ A “local” importer
§ Importing the package locally by persisting it into the
Sling instance
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17. Replication agents
§ A “coordinating” agent has
§ A “remote” exporter
§ Pulling a package from a remote endpoint
§ A “remote” importer
§ Importing the package remotely into a Sling instance
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18. Replication agents
§ A “queuing” agent has
§ A “local” exporter
§ Creating a package locally for the resources to be
replicated (e.g. from the underlying JCR repo)
§ No importer
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19. Replication package serialization
§ Payload to be sent / received
§ Package builders for (de)serialization
§ Jackrabbit FileVault based package builder
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20. Replication queues
§ Multiple queue providers
§ Sling Jobs based (sling.event bundle)
§ In memory
§ Multiple queue distribution strategies
§ Single
§ Error aware
§ Priority
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21. Replication rules
§ Rules can be defined within agents
§ To trigger replications upon resource changes
§ To schedule periodic replications
§ To chain replicate
§ ...
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22. Accessing replication resources
§ Agents as OSGi services
§ Can be defined via ConfigurationAdmin
§ Resource providers control
§ Service access
§ CRUD operations on configs
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23. Agent configuration example (1/3)
§ Config for a ‘push agent’
{
"jcr:primaryType" : "sling:OsgiConfig",
"name" : "publish",
"type" : "simple",
"packageExporter": [
"type=local”,
"packageBuilder/type=vlt",
...
],
...
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24. Agent configuration example (2/3)
...
"packageImporter" : [
"type=remote",
"endpoints[0]=http://.../replication/services/importers/default”,
"authenticationFactory/type=service",
"authenticationFactory/name=user",
...
"packageBuilder/type=vlt",
...
],
...
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25. Agent configuration example (3/3)
...
"queueProvider" : [
"type=service",
"name=sjh"
],
"queueDistributionStrategy" : [
"type=service",
"name=error"
]
}
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26. Anatomy of a forward replication request
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27. Anatomy of a fwd. replication (1/4)
§ HTTP POST on /libs/sling/replication/
service/agents/publish with form parameters
§ Action = ADD
§ Path = /content/replication
§ Agent with name ‘publish’ gets picked up by
the agent resource provider
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28. Anatomy of a fwd. replication (2/4)
§ Agent ‘publish’ calls its Exporter (local) to
create the payload
§ the ‘local’ exporter calls its Package builder
§ the ‘vlt’ package builder creates a FileVault
package for resources under /foo/bar
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29. Anatomy of a fwd. replication (3/4)
§ Agent ‘publish’ dispatches the package to its
queue provider and distribution algorithm
§ The queue provider is asked to provide queues
depending on the distribution strategy
§ The request gets queued
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30. Anatomy of a fwd. replication (4/4)
§ When queue entry gets processed the
(remote) importer is called
§ Package sent over the wire to an endpoint bound to a
local importer on the receiving server
§ The local importer on the receiving side deserializes
and persists the replication package via its package
builder
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31. Reverse replication
§ Pull agent on author
§ Periodically polling
§ Queuing agent on publish
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32. Event based reverse replication
§ No scheduled polling
§ The publish instance notifies author when to
pull
§ Notification through server sent events
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33. Looking forward
§ Get information on other instances
§ e.g. replicate to all instances with run mode ‘xyz’
§ NRT publish sync
§ Coordinate agents++
§ Performance
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34. Thanks!
§ Questions?
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