Apache Solr is an open source enterprise search service from the Lucene project. Solr is written in Java and runs as a standalone full-text search server within a servlet container such as Tomcat.

Like any service or component in your architecture, you’ll want to monitor it to ensure that it’s available and gather performance data to help with tuning.

In this post, we’ll look at how we can monitor Solr, what performance metrics we might want to gather and how we can easily achieve this with Opsview.


A check list for service checks

Solr is built on Lucene so follows the same layout, an index contains documents that are comprised of fields. As part of the search service value add over Lucene, Solr provides a number of useful ways of obtaining health status / monitoring metrics:
  • Health-check status using the /admin/ping handler
  • The admin statistics page /admin/stats.jsp (XML styled with XSL)
  • JMX MBeans
The list of applicable checks could be defined by whether it is a health check or a data gathering check - but this would lead to a lot of overlap.

Instead the list is divided into the checks that can be performed remotely (without an installed agent on the server) and those that are best performed locally to the Solr server.

Remote (agent-less) checks

What should we look for over the network?

Firstly we can have a host-level check which may perform a network level ping. Next we can check TCP connectivity to the servlet container port and then make an HTTP GET request to the Solr ‘front page’ and check for a known string (e.g. Welcome to Solr).

Now we’ve made it up to the application layer so can start to perform Solr specific checks. Items to monitor may include (delete as applicable):
  • Ping status
  • Number of docs
  • Number of queries / queries per second
  • Average response time
  • Number of updates
  • Cache hit ratios
  • Replication status
  • Synthetic queries

Agent-based checks

Installing an Opsview agent on the Solr server means we can run additional checks over NRPE (Nagios Remote Plugin Executor). This could be operating system level checks such as memory/disk utilisation or CPU load, or the following:
  • Java servlet container process is running
  • JMX checks e.g. heap memory or custom MBeans
  • File age
  • Log parsing for exceptions
The Solr wiki describes how to configure JMX support:

Opsview configuration

For the rest of this article you'll need to have Opsview installed (or the Opsview VMWare appliance) and have completed the Quick Start.

Solr-specific Plugin

Install the Solr plugin at into /usr/local/nagios/libexec/

The check_solr plugin was developed using Perl, so that it could be contributed back to Opsview. It requires the CPAN XML::XPath module (sudo cpan -i XML::XPath).

The plugin includes usage instructions, check_solr -h which can also be viewed in Opsview by selecting the ‘Show Plugin Help‘ link beneath the Plugin drop down (see Figure 1). The -u option can be used to specify the URL path for multi-core set-ups.

Service check setup

Figure 1 gives an example of a service check configuration.
Opsview service check configuration.

Figure 2 shows the agentless service check group with plugins and their arguments.

solr agentless monitoring

Host configuration

Figure 3 shows a simplistic host setup with a ping check.

set up host

Figure 4 is an extract from the Monitors tab, where we select the checks we want performed for  for the current host.


Viewing output

The check results shown in Figure 5 are visible by navigating through the host group hierarchy.

If you click on the graph icon of Solr Cache Hit Ratios this will drill down onto the graph shown in Figure 6. Clicking on the graph icon for Solr Avg Response Time - standard will take you to the graphs in Figure 7.

cache hit ratios average request time

If you shutdown Solr, then the check results will start to turn critical and show in red as per Figure 8.

post shoutdown alert


There are a few other plugins available for monitoring Solr from Opsview, depending on your needs:

Also, chapter 8 of the recently published Apache Solr 3 Enterprise Search Server book includes a section on Monitoring Solr Performance.


Using check_solr in conjunction with Opsview allows you to ensure that your Solr server is available and provides you with metrics that can help you tune your Solr configuration. This can be complemented with additional agent-based operating system and JMX checks to give you a full picture view.

About the Author

Robin Bramley is a hands-on Technical Manager / Lead Architect at an Open Source software & services company who has spent the majority of the last decade working with Java, mobile & Open Source across sectors including Financial Services & High Growth / start-ups.

Legal Disclaimer

This blog post is contributed by a member of the Opsview community. The Opsview project and Opsera Ltd accept no responsibility for the accuracy of its content and are not liable for any direct or indirect damages caused by its use.