Apache Solr Reference Guide Covering Apache Solr 6.0

Collection creation
Shard creation
Replica creation
Shard splitting
Common Use Cases
There are several situations where this functionality may be used. A few of the rules that could be implemented
are listed below:
Don’t assign more than 1 replica of this collection to a host.
Assign all replicas to nodes with more than 100GB of free disk space or, assign replicas where there is
more disk space.
Do not assign any replica on a given host because I want to run an overseer there.
Assign only one replica of a shard in a rack.
Assign replica in nodes hosting less than 5 cores.
Assign replicas in nodes hosting the least number of cores.
Rule Conditions
A rule is a set of conditions that a node must satisfy before a replica core can be created there.
Rule Conditions
There are three possible conditions.
shard: this is the name of a shard or a wild card (* means for all shards). If shard is not specified, then the
rule applies to the entire collection.
replica: this can be a number or a wild-card (* means any number zero to infinity).
tag: this is an attribute of a node in the cluster that can be used in a rule, e.g. “freedisk”, “cores”, “rack”,
“dc”, etc. The tag name can be a custom string. If creating a custom tag, a snitch is responsible for
providing tags and values. The section Snitches below describes how to add a custom tag, and defines
six pre-defined tags (cores, freedisk, host, port, node, and sysprop).
Rule Operators
A condition can have one of the following operators to set the parameters for the rule.
equals (no operator required): tag:x means tag value must be equal to ‘x’
greater than (>): tag:>x means tag value greater than ‘x’. x must be a number
less than (