Shared storage master slave broker topologies depend on successful storage locking. Meaning that only a single broker (the master) is active and use the message database. So far locking was tied to a specific message store, so KahaDB was using shared file locking while JDBC store was using a specialized database table to keep slaves from starting. This work fine for the most use cases, but sometimes folks need to use a custom locker (like when the standard file locking doesn’t work on their NFS) or tune existing solutions.

For the upcoming 5.7.0 release we introduced pluggable storage lockers, which means that message storage locking is totally separated from the store itself. That means that you can now use any locking strategy with any store. An example configuration is shown below:

<persistenceAdapter>
    <kahaDB directory = "target/activemq-data">
        <locker>
            <shared-file-locker lockAcquireSleepInterval="5000"/>
        </locker>
    </kahaDB>
</persistenceAdapter>

You can find more details on this new feature here. It will also allow us to implement new locking strategies, based on ZooKeeper for example, which will make high-availability setups even easier. So stay tuned.