Configuring the Solr heartbeat mechanism

Setting up the heartbeat mechanism in Solr is very easy. One just needs to add the following section to the solrconfig.xml file:

<requestHandler name="/admin/ping" class="solr.PingRequestHandler">
 <lst name="invariants">
  <str name="q">solrpingquery</str>
 </lst>
</requestHandler>

This is all. Of course, if we need all our cores and collections to respond to the health requests, we should include the previous section in the solrconfig.xml files for all of them. After this, run a query to the admin/ping handler of our Solr instance, for example:

curl 'localhost:8983/solr/heartbeat_core/admin/ping'

Solr will respond with a status response, for example:

<?xml version="1.0" encoding="UTF-8"?>
<response>
<lst name="responseHeader"><int name="status">0</int><int name="QTime">6</int><lst name="params"/></lst><str name="status">OK</str>
</response>

The configuration is really simple; we defined a new request handler that will be available under the /admin/ping address (of course, we have to prefix it with the host address and core name). The class implementing the handle is the one dedicated to handle the heartbeat mechanism request, solr.PingRequestHandler. We also defined that the q parameter for all the ping requests will be solrpingquery and the request won't be able to overwrite this parameter (because we included it in the invariants section). The ping query should be as simple as it can get so that it runs blazingly fast; what's more, it is usually good for it not to return any search results.

As you can see, the response contains the status section, which in our case has the value of OK. In the case of an error, the status section will contain the error code.

The solr.PingRequestHandler handler allows us to enable and disable the heartbeat mechanism without shutting down the whole Solr instance.

<requestHandler name="/admin/ping" class="solr.PingRequestHandler">
 <lst name="invariants">
  <str name="q">solrpingquery</str>
 </lst>
 <str name="healthcheckFile">server-enabled.txt</str>
</requestHandler>

curl 'localhost:8983/solr/heartbeat_core/admin/ping?action=enable'

curl 'localhost:8983/
solr/heartbeat_core/admin/ping?action=disable'

curl 'localhost:8983/solr/heartbeat_core/admin/ping?action=status'