Failover when clusterA is down

Failover when `clusterA` is down

You can simulate this by shutting down either of the clusters. Let’s shut down cluster A in this tutorial.
Start Logstash with the same configuration file. (This step is not required in real use cases where Logstash ingests continuously.)
```
### On Logstash server ###
bin/logstash -f multiple_hosts.conf
```
Observe all Logstash traffic will be redirected to cluster B automatically.

You should also redirect all search traffic to the clusterB cluster during this time.
The two data streams on cluster B now contain a different number of documents.
- data streams on cluster A (down)
  - 50 documents in logs-generic-default-replicated_from_clusterb
  - 50 documents in logs-generic-default
- data streams On cluster B (up)
  - 50 documents in logs-generic-default-replicated_from_clustera
  - 150 documents in logs-generic-default