The document summarizes a presentation on distributed eventing and jobs using Apache Sling and OSGi technologies. It discusses how OSGi event publishing works, Apache Sling discovery and job handling capabilities, and how events can be used to trigger and distribute jobs across multiple instances in a clustered environment. Key points include how Sling identifies instances, clusters, and topologies, manages job queues and consumers, and distributes jobs based on enabled topics and instance availability.

1. APACHE SLING & FRIENDS TECH MEETUP
BERLIN, 23-25 SEPTEMBER 2013
Distributed Eventing and Jobs
Carsten Ziegeler | Adobe Research Switzerland
1

2. About
2
§ RnD Team at Adobe Research Switzerland
§ Co-founder Adobe Granite
§ OSGi Core Platform and Enterprise Expert
Groups
§ Member of the ASF
§ Current PMC Chair of Apache Sling
§ Apache Sling, Felix, ACE
§ Conference Speaker
§ Technical Reviewer
§ Article/Book Author

3. Overview
3
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing

4. Overview
4
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing

5. OSGi Event Admin
Publish Subscribe Model
5
OSGi
Event
Admin
Component
A
publish
deliver
Component
X
Component
Y

6. OSGi Event Admin
Publish Subscribe Model
6
§ OSGi event is a data object with
§ Topic (hierarchical namespace)
§ Properties (key-value-pairs)
§ Resource Event
§ Topic:
org/apache/sling/api/resource/Resource/ADDED
§ Properties: path, resource type etc.

7. OSGi Event Admin
Publish Subscribe Model
7
§ Publisher creates event object
§ Sends event through EventAdmin service
§ Either sync or async delivery
§ Subscriber is an OSGi service
(EventHandler)
§ Service registration properties
§ Interested topic(s)
§ org/apache/sling/api/resource/Resource/*
§ Additional filters (optional)
§ (path=/libs/*)

8. OSGi Event Admin
Publish Subscribe Model
8
§ Immediate delivery to available
subscribers
§ No guarantee of delivery
§ No distributed delivery

9. OSGi Event Admin
Publish Subscribe Model
9
§ Immediate delivery to available
subscribers
§ No guarantee of delivery
§ No distributed delivery
Discovery
Sling
Job
Distribu3on

10. Overview
10
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing

11. Overview
11
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing

12. Installation Scenarios
12
Clustered
JCR
Single
Instance
JCR
Instance
1
Instance
2
Instance
3

13. Topologies I
Apache Sling Discovery
13
Clustered
JCR
JCR
ID
:
A
ID
:
X
ID
:
42
ID
:
1
Single
Instance
Instance
1
Instance
2
Instance
3
§ Instance: Unique Id (Sling ID)

14. Topologies I
Apache Sling Discovery
14
§ Instance: Unique Id (Sling ID)
§ Cluster: Unique Id and leader
Cluster
99
Cluster
35
Clustered
JCR
JCR
ID
:
A
ID
:
X
ID
:
42
ID
:
1
Single
Instance
Instance
1
Instance
2
Instance
3
Leader
Leader

15. Topologies I
Apache Sling Discovery
15
§ Topology: Set of clusters
Cluster
99
Cluster
35
Clustered
JCR
JCR
ID
:
A
ID
:
X
ID
:
42
ID
:
1
Single
Instance
Instance
1
Instance
2
Instance
3
Leader
Leader
Topology
Topology

16.
Cluster
99
Cluster
35
Topologies I
Apache Sling Discovery
16
Clustered
JCR
JCR
ID
:
A
ID
:
X
ID
:
42
ID
:
1
Single
Instance
Instance
1
Instance
2
Instance
3
Leader
Leader
Topology
§ Topology: Set of clusters

17. Topologies II
Apache Sling Discovery
17
§ Instance
§ Sling ID
§ Optional:
Name and description
§ Belongs to a cluster
§ Might
be
the
cluster
leader
§ Additional distributed properties
§ Extensible
through
own
services
(PropertyProvider)
§ E.g.
data
center,
region
or
enabled
job
topics
Cluster
99
ID
:
42
Instance
3
Topology
Lead
er

18. Topologies II
Apache Sling Discovery
18
§ Cluster
§ Elects (stable) leader
§ Stable instance ordering
Cluster
99
ID
:
42
Instance
3
Topology
Lead
er

19. Topologies II
Apache Sling Discovery
19
§ TopologyEventListener
§ Receives events on
topology changes
§ Topology is changing
§ Topology changed
§ Properties changed
Cluster
99
ID
:
42
Instance
3
Topology
Lead
er

20. Overview
20
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing

21. Job Handling I
Apache Sling Job Handling
21
§ Job : Guaranteed processing,
exactly once
§ Exactly one job consumer
§ Started by client code, e.g. for
replication, workflow...
§ Job topic
§ Payload is a serializable map

22. Job Handling I
Apache Sling Job Handling
22
§ Sling Job Manager handles and
distributes jobs
§ Delivers job to a job consumer…
§ …and waits for response
§ Retry and failover
§ Notification listeners (fail, retry,
success)

23. Starting / Processing a Job I
Apache Sling Job Handling
23
public interface JobConsumer {
String PROPERTY_TOPICS = "job.topics";
enum JobResult {
OK,
FAILED,
CANCEL,
ASYNC
}
JobResult process(Job job);
}
public interface JobManager {
Job addJob(String topic, String optionalName, Map<String, Object> properties);
…
}
Star3ng
a
job
Processing
a
job
Note:
Star3ng/processing
of
jobs
through
Event
Admin
is
deprecated
but
s3ll
supported

24. Starting / Processing a Job II
Apache Sling Job Handling
24
@Component
@Service(value={JobConsumer.class})
@Property(name=JobConsumer.PROPERTY_TOPICS, value="org/apache/sling/jobs/backup")
public class BackupJobConsumer
implements JobConsumer {
@Override
public JobResult process(final Job job) {
// do backup
return JobResult.OK;
}
}

25. Job Handling I
Apache Sling Job Handling
25
• New jobs are immediately persisted
• Jobs are “pushed” to the processing
instance
• Processing instances use different
queues
• Associated with job topic(s)
• Main queue
• 0..n custom queues

26. Job Queue I
Apache Sling Job Handling
26
• Queue is configurable
• Queue is started on demand in own
thread
• And stopped if unused for some time

27. Job Queue II
Apache Sling Job Handling
27
• Queue Types
• Ordered queue
• Parallel queues: Plain and Topic Round
Robin

28. Job Queue III
Apache Sling Job Handling
28
• Limit for parallel threads per queue
• Number of retries (-1 = endless)
• Retry delay
• Thread priority

29. Additional Configurations
Apache Sling Job Handling
29
• Job Manager Configuration = Main
Queue Configuration
• Maximum parallel jobs (15)
• Retries (10)
• Retry Delay
• Eventing Thread Pool Configuration
• Used by all queues
• Pool size (35) = Maximum parallel jobs for
a single instance

30. Monitoring – Web Console
Apache Sling Job Handling
30

31. Monitoring – Web Console
Apache Sling Job Handling
31

32. Job Distribution I
Apache Sling Job Distribution
32
• Each instance determines enabled job
topics
• Derived from Job Consumers (new API
required)
• Can be whitelisted/blacklisted (in Job
Consumer Manager)
• Announced through Topology

33. Job Distribution II
Apache Sling Job Distribution
33
• Job Distribution depends on enabled
job topics and queue type
• Potential set of instances derived from
topology (enabled job topics)
• Ordered: processing on leader only, one job
after the other
• Parallel: Round robin distribution on all
potential instances
§ Local
cluster
instances
have
preference

34. Job Distribution III
Apache Sling Job Distribution
34
• Failover
• Instance crash: leader redistributes jobs to
available instances
§ Leader
change
taken
into
account
• On enabled job topics changes:
potential redistribution

35. Sling Job Distribution
35
Topology
Instance
Sling
ID:
1
Job
Manager
Instance
Sling
ID:
2
Job
Manager
Instance
Sling
ID:
3
Job
Manager
Instance
Sling
ID:
4
Job
Manager
Job
Consumer
Topic:
A
Job
Consumer
Topic:
B
Job
Consumer
Topic:
C

36. Sling Job Distribution
36
Instance
Sling
ID:
1
Job
Manager
Instance
Sling
ID:
2
Job
Manager
Instance
Sling
ID:
3
Job
Manager
Instance
Sling
ID:
4
Job
Manager
A
Job
Consumer
Topic:
A
Job
Consumer
Topic:
B
A:2
Job
Consumer
Topic:
C
Job
Topology

37. Sling Job Distribution
37
Instance
Sling
ID:
1
Job
Manager
Instance
Sling
ID:
2
Job
Manager
Instance
Sling
ID:
3
Job
Manager
Instance
Sling
ID:
4
Job
Manager
B
Job
Consumer
Topic:
A
Job
Consumer
Topic:
B
B:3
Job
Consumer
Topic:
C
Job
Topology

38. Sling Job Distribution
38
Instance
Sling
ID:
1
Job
Manager
Instance
Sling
ID:
2
Job
Manager
Instance
Sling
ID:
3
Job
Manager
Instance
Sling
ID:
4
Job
Manager
C
Job
Consumer
Topic:
A
Job
Consumer
Topic:
B
C:4
Job
Consumer
Topic:
C
Job
?
Topology

39. Discovery and Eventing
39
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing

40. Discovery and Eventing – What’s Next?
40
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing
New
OSGi
Specifica-on
• Distributed
Even3ng
• Cloud
Compu3ng

41. Discovery and Eventing – What’s Next?
41
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing
Job
Distribu-on
• Improved
load
balancing
• Pull
based
distribu3on

42. One More Thing…
42
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing

43. Job Progress Tracking
Apache Sling Job Processing
43
§ Jobs can inform about
§ Progress (percentage)
§ ETA
§ Additional informational messages
§ All information is persisted
NEW

44. Improved Failure Handling I
Apache Sling Job Processing
44
§ Currently, no history of jobs
§ Immediately removed once
§ Job succeeds
§ Job is cancelled
§ What happened?
§ What did go wrong?

45. Improved Failure Handling II
Apache Sling Job Processing
45
§ Cancelled jobs are kept
§ With a reason and log
§ Can be retried
§ Successful jobs can be kept
§ With a message and log
NEW

46. Discovery and Eventing
46
Discovery
Sling
Job
Distribu3on
Felix
OSGi
Event
Admin
From
Even3ng
to
Job
Processing