1. Replicated LevelDB on JBoss Fuse
Jakub Knetl
Red Hat
2018/5/14

2. Messaging systems Mechanisms for exchanging data (messages)
Advantages:
Clients can communicate asynchronously
Wide set of (platform independent) clients
Reliability
Scalability
What is messaging system
Why to use it instead of direct data exchange

3. Basic concepts Message Header Body (content) Destination Clients
Producer
Consumer

4. Point to point comunication
Queue destination
One of consumers gets message
Load is distributed across consumers
Message is stored until some consumer receives it

5. Point to point communication
Consumers
Producer
Queue

6. Publish subscribe communication
Message is delivered to all subscribers
When no subscriber connected message is thrown away
Special case – durable subscriber

7. Publish/subscribe
Subscribers
Publisher
Topic

8. JBoss Fuse Open-source ESB Messaging system based on Apache ActiveMQ
Runs in OSGI container
Integration framework
Webservices
Easy cluster deployment
Lots of componetns
Integrated in OSGI container
WebConsole
Fabric

9. JBoss Fuse

10. High availability Messaging systems processes business critical data
Server must be accessible 24/7
Various mechanisms to ensure HA

11. Introduction to HA in ActiveMQ
Group of brokers forms logically one broker
Master broker
Communicates with clients
Slave brokers
Passive
Clients cannot connects to it
Election mechanism
Client reconnects in case of failure
Message acknowledgment after the message is stored safely
Important note: Multiple brokers forms logically one broker

12. Different topologies Shared JDBC master/slave
Shared file system master/slave
Replicated levelDB master/slave (shared nothing)

13. Shared JDBC You need shared database Locking on database
Reliable, but rather slow
Single point of failure

14. Shared JDBC
Client
Master
Master
Brokers
Database

15. Shared file system Convenient when having SAN Faster than JDBC
Needs file system with reliable locking!
Single point of failure

16. Shared filesystem
Client
Master
Master
Brokers
Shared FS

17. Replicated LevelDB Shared nothing No single point of failure!
Servers coordinates themselves by exchanging messages (replication protocol)
Needs Zookeeper server

18. Choosing master That's why ZooKeeper is important
Brokers register themselves at zookeeper
Zookeeper decides who will become master

19. Replication protocol Slave brokers connects to the master
Messages are replicated to slaves
Message acknowledgment after replicating at least to quorum of brokers (N/2 - 1).

20. Replicated LevelDB A B
Master C
Master

21. Demo