Package org.apache.solr.handler

Class PingRequestHandler

java.lang.Object
org.apache.solr.handler.RequestHandlerBase
org.apache.solr.handler.PingRequestHandler
All Implemented Interfaces:
AutoCloseable, ApiSupport, SolrInfoBean, NestedRequestHandler, SolrMetricProducer, SolrRequestHandler, PermissionNameProvider, SolrCoreAware
public class PingRequestHandler extends RequestHandlerBase implements SolrCoreAware
Ping Request Handler for reporting SolrCore health to a Load Balancer.

This handler is designed to be used as the endpoint for an HTTP Load-Balancer to use when checking the "health" or "up status" of a Solr server.

In its simplest form, the PingRequestHandler should be configured with some defaults indicating a request that should be executed. If the request succeeds, then the PingRequestHandler will respond back with a simple "OK" status. If the request fails, then the PingRequestHandler will respond back with the corresponding HTTP Error code. Clients (such as load balancers) can be configured to poll the PingRequestHandler monitoring for these types of responses (or for a simple connection failure) to know if there is a problem with the Solr server.

Note in case isShard=true, PingRequestHandler respond back with what the delegated handler returns (by default it's /select handler). 

 <requestHandler name="/admin/ping" class="solr.PingRequestHandler">
   <lst name="invariants">
     <str name="qt">/search</str><!-- handler to delegate to -->
     <str name="q">some test query</str>
   </lst>
 </requestHandler>

A more advanced option available, is to configure the handler with a "healthcheckFile" which can be used to enable/disable the PingRequestHandler. 

 <requestHandler name="/admin/ping" class="solr.PingRequestHandler">
   <!-- relative paths are resolved against the data dir -->
   <str name="healthcheckFile">server-enabled.txt</str>
   <lst name="invariants">
     <str name="qt">/search</str><!-- handler to delegate to -->
     <str name="q">some test query</str>
   </lst>
 </requestHandler>
  • If the health check file exists, the handler will execute the delegated query and return status as described above.
  • If the health check file does not exist, the handler will return an HTTP error even if the server is working fine and the delegated query would have succeeded

This health check file feature can be used as a way to indicate to some Load Balancers that the server should be "removed from rotation" for maintenance, or upgrades, or whatever reason you may wish.

The health check file may be created/deleted by any external system, or the PingRequestHandler itself can be used to create/delete the file by specifying an "action" param in a request:

  • http://.../ping?action=enable - creates the health check file if it does not already exist
  • http://.../ping?action=disable - deletes the health check file if it exists
  • http://.../ping?action=status - returns a status code indicating if the healthcheck file exists ("enabled") or not ("disabled")
Since:
solr 1.3