TopologyValidator (Ignite 2.17.0)

All Superinterfaces:

Serializable
```
public interface TopologyValidator
extends Serializable
```
Topology validator is used to verify that cluster topology is valid for further cache operations. The topology validator is invoked every time the cluster topology changes (either a new node joined or an existing node failed or left).
If topology validator is not configured, then the cluster topology is always considered to be valid.
Whenever the validate(Collection) method returns true, then the topology is considered valid for a certain cache and all operations on this cache will be allowed to proceed. Otherwise, all update operations on the cache are restricted with the following exceptions:
- CacheException will be thrown for all update operations (put, remove, etc) attempt.
- IgniteException will be thrown for the transaction commit attempt.
After returning false and declaring the topology not valid, the topology validator can return to normal state whenever the next topology change happens.
Example
The example below shows how a validator can be used to allow cache updates only in case if the cluster topology contains exactly 2 nodes:
```
 new TopologyValidator() {
    public boolean validate(Collection nodes) {
       return nodes.size() == 2;
    }
 }
 
```
Configuration
The topology validator can be configured either from code or XML via CacheConfiguration.setTopologyValidator(TopologyValidator) method.

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  boolean validate(Collection<ClusterNode> nodes)
  Validates topology.

- Method Detail
  - validate
```
boolean validate(Collection<ClusterNode> nodes)
```
    Validates topology.
    
    Parameters:
    
    nodes - Collection of nodes.
    
    Returns:
    
    true in case topology is valid for specific cache, otherwise false