Cluster Sharding(2.4, Java/Groovy)-how to avoid a rebalance during a rolling release?

[Michael Kohout]

Hi All-

I'm prototyping a system that will use cluster sharding at a shop where Operations generally does rolling deployments-so it deploys an application one host(of a cluster) at a time.

Is there any way to have Akka avoid rebalancing during these events?  Something that will give us a 20 minute window to do a single machine deployment?

thanks for any suggestions

Michael Kohout

[Martynas Mickevičius]

Hi,

you can provide a custom shard allocation strategy that during rolling release returns empty set of shards that need to be rebalanced.

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[Siva Kommuri]

Interesting. Could you kindly elaborate?

Best wishes,

Siva on 6+

[Patrik Nordwall]

Custom shard allocation strategy can be defined in an optional parameter to ClusterSharding.start. See the API documentation of ShardAllocationStrategy for details of how to implement a custom shard allocation strategy.

http://doc.akka.io/docs/akka/2.4.7/scala/cluster-sharding.html#Configuration

The allocation strategy returns a Future, so you can delegate the call to an Actor, using ask. The actor could be controlled by the operator, e.g. via HTTP or JMX API.

/Patrik

Patrik Nordwall
Akka Tech Lead
Lightbend -  Reactive apps on the JVM
Twitter: @patriknw