Now we illustrate the most amazing feature of Swarm Mode--the scale command. We restore the configuration we had before trying Flocker, so we destroy the spark-worker service and re-create it with a replica factor of 3:

aws-101$ docker service create \
--constraint 'node.labels.type != sparkmaster' \
--network spark \
--name spark-worker \
--replicas 3 \
--env SPARK_MASTER_IP=10.0.0.3 \
--env SPARK\_WORKER\_CORES=1 \
--env SPARK\_WORKER\_MEMORY=1g \
fsoppelsa/spark-worker

Now, we scale up the service with 30 Spark workers using the following code:

aws-101$ docker service scale spark-worker=30

After some minutes, necessary to eventually pull the image, we check once again:

From the Spark web UI:

Scale can be used to scale up or down the size of the replicas. So far, still there are no automated mechanisms for auto-scaling or for distributing the load to newly added nodes. But they can be implemented with custom utilities, or we may even expect them to be integrated into Swarm...