Shawn Heisey elyograg at
Wed Jul 10 18:19:14 EEST 2019

On 7/10/2019 2:49 AM, Maciej Milaszewski IQ PL via dovecot wrote:
> On the other hand solr replication is quite complicated process and
> rollback or master-slave switch in this case is non-trivial task, that
> may have result in whole dataset inconsistency.
> Do you have any experience in such cases ? Maby load-balance in HAProxy
> colud do the thing ? Something like:
> .........
> server search1 check port 8983 inter 20s fastinter 2
> server search2 backup
> .........

If you are using master-slave replication, you do not want to do this. 
Say the master went down, and it took you a while to get it back up. 
Unless you change the replication config, any data indexed on the slave 
would be gone as soon as the master was started back up, because the 
index would be replicated from the master.  You are quite correct that 
switching replication roles is non-trivial.

Using a load balancer in this manner is a great option if Solr is 
running in SolrCloud mode.  SolrCloud is a true cluster -- no masters, 
no slaves.  You can send indexing or queries to any system in the cloud 
and everything works.  The only real downside is that ZooKeeper (which 
is what turns Solr into SolrCloud) requires three servers for high 
availability, not two.  The third server could have much lower specs 
than the other two, as ZooKeeper's system requirements are typically 
quite modest.


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