Ping queries are used in Solr to monitor the health of the Solr server. Let us first see how the ping query works on the Solr Admin web interface:

Let us check the version of PHP installed. We need Version 5.3.2 and above. To check the version, run php –v on the Windows or Linux command line as follows:

c:\>php -v
PHP 5.4.16 (cli) (built: Jun  5 2013 21:01:46)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2013 Zend Technologies

To get ping working from our PHP code, we will need a utility called cURL. For Linux environments, we need to install the curl, libcurl, and php5-curl packages. On Ubuntu distribution of Linux it can be installed using the following command:

sudo apt-get install curl php5-curl

For enabling cURL on windows, we need to edit the php.ini file in our PHP installation. Search for the extensions directory setting and change it to where php_curl.dll is located. Also, uncomment the line which loads php_curl.dll:

extension=php_curl.dll
extension_dir = "C:\php\ext"

The following URL is the URL that is being called for executing the ping query. On going to this URL, we can see the response that contains the response header and the status, which is OK.

http://localhost:8080/solr/collection1/admin/ping

We can see that the response is in XML. To convert the response to JSON, simply add wt=json to the earlier URL:

http://localhost:8080/solr/collection1/admin/ping/?wt=json

Linux users can check the response of a curl call using the following command:

curl http://localhost:8080/solr/collection1/admin/ping/?wt=json
{"responseHeader":{"status":0,"QTime":7,"params":{"df":"text","echoParams":"all","rows":"10","echoParams":"all","wt":"json","q":"solrpingquery","distrib":"false"}},"status":"OK"}

A direct call to Solr via PHP requires us to call the ping with a JSON response URL via cURL and decode the JSON response to show the result. Here is a piece of code to do the same. This code can be executed using the PHP command line:

$curl = curl_init("http://localhost:8080/solr/collection1/admin/ping/?wt=json");
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($curl);
$data = json_decode($output, true);
echo "Ping Status : ".$data["status"]."\n";

On executing the preceding code via command line, we will get the output as follows:

Ping Status : OK