= Monitoring Solr with Prometheus and Grafana
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You can monitor Solr using solr-exporter that exposes Solr's metrics to https://prometheus.io[Prometheus], and visualize metrics using https://grafana.com[Grafana].

It allows users to monitor not only Solr metrics which come from <<metrics-reporting.adoc#metrics-api,Metrics API>> but also facet counts which come from <<searching.adoc#searching,Searching>>.

.solr-exporter Diagram
image::images/monitoring-solr-with-prometheus-and-grafana/solr-exporter-diagram.png[image,width=600]

This feature is experimental status.

== Running solr-exporter

You can start solr-exporter by running `./bin/solr-exporter` from the solr-exporter directory.

[source,plain]
----
$ cd ./contrib/prometheus-exporter
$ ./bin/solr-exporter -p 9983 -b http://localhost:8983/solr -f ./conf/solr-exporter-config.xml -n 8
----

If you are on Windows platform, you can start solr-exporter by running `.\bin\solr-exporter.cmd` instead.

[source,plain]
----
> cd .\contrib\prometheus
> .\bin\solr-exporter.cmd -p 9983 -b http://localhost:8983/solr -f .\conf\solr-exporter-config.xml -n 8
----

You can also connect to Solr in SolrCloud mode like this.

[source,plain]
----
$ cd ./contrib/prometheus
$ ./bin/solr-exporter -p 9983 -z localhost:2181/solr -f ./conf/solr-exporter-config.xml -n 16
----

See command help:

[source,plain]
----
$ ./bin/solr-exporter -h
usage: SolrCollector [-h] [-v] [-p PORT] [-b BASE_URL] [-z ZK_HOST] [-f CONFIG]
                     [-n NUM_THREADS]

Prometheus exporter for Apache Solr.

optional arguments:
  -h, --help             show this help message and exit
  -p PORT, --port PORT   solr-exporter listen port
  -b BASE_URL, --baseurl BASE_URL
                         specify Solr base URL when connecting  to Solr in standalone mode (for
                         example 'http://localhost:8983/solr')
  -z ZK_HOST, --zkhost ZK_HOST
                         specify  ZooKeeper  connection  string  when  connecting  to  Solr  in
                         SolrCloud mode (for example 'localhost:2181/solr')
  -f CONFIG, --config-file CONFIG
                         specify configuration file
  -n NUM_THREADS, --num-thread NUM_THREADS
                         specify number of threads
----

The Solr's metrics exposed by solr-exporter can see at the following URL.

http://localhost:9983/metrics[http://localhost:9983/metrics]


== solr-exporter Configuration

The configuration is in `./config/solr-exporter-config.xml`. An example with all possible options:

[source,xml]
----
<config>

  <rules>

    <ping>
      <lst name="request">
        <lst name="query">
          <str name="path">/admin/ping</str>
        </lst>
        <arr name="jsonQueries">
          <str>
            . as $object | $object |
            (if $object.status == "OK" then 1.0 else 0.0 end) as $value |
            {
              name         : "solr_ping",
              type         : "GAUGE",
              help         : "See following URL: https://lucene.apache.org/solr/guide/ping.html",
              label_names  : [],
              label_values : [],
              value        : $value
            }
          </str>
        </arr>
      </lst>
    </ping>

    <metrics>
      <lst name="request">
        <lst name="query">
          <str name="path">/admin/metrics</str>
          <lst name="params">
            <str name="group">all</str>
            <str name="type">all</str>
            <str name="prefix"></str>
            <str name="property"></str>
          </lst>
        </lst>
        <arr name="jsonQueries">
          <!--
            jetty metrics
          -->
          <str>
            .metrics["solr.jetty"] | to_entries | .[] | select(.key | startswith("org.eclipse.jetty.server.handler.DefaultHandler")) | select(.key | endswith("xx-responses")) as $object |
            $object.key | split(".") | last | split("-") | first as $status |
            $object.value.count as $value |
            {
            name         : "solr_metrics_jetty_response_total",
            type         : "COUNTER",
            help         : "See following URL: https://lucene.apache.org/solr/guide/metrics-reporting.html",
            label_names  : ["status"],
            label_values : [$status],
            value        : $value
            }
          </str>

...

        </arr>
      </lst>
    </metrics>

    <collections>
      <lst name="request">
        <lst name="query">
          <str name="path">/admin/collections</str>
          <lst name="params">
            <str name="action">CLUSTERSTATUS</str>
          </lst>
        </lst>
        <arr name="jsonQueries">
          <str>
            .cluster.live_nodes | length as $value|
            {
              name         : "solr_collections_live_nodes",
              type         : "GAUGE",
              help         : "See following URL: https://lucene.apache.org/solr/guide/collections-api.html#clusterstatus",
              label_names  : [],
              label_values : [],
              value        : $value
            }
          </str>

...

        </arr>
      </lst>
    </collections>

    <search>
      <lst name="request">
        <lst name="query">
          <str name="collection">collection1</str>
          <str name="path">/select</str>
          <lst name="params">
            <str name="q">*:*</str>
            <str name="start">0</str>
            <str name="rows">0</str>
            <str name="json.facet">
              {
                category: {
                  type: terms,
                  field: cat
                }
              }
            </str>
          </lst>
        </lst>
        <arr name="jsonQueries">
          <str>
            .facets.category.buckets[] as $object |
            $object.val as $term |
            $object.count as $value |
            {
              name         : "solr_facets_category",
              type         : "GAUGE",
              help         : "Category facets",
              label_names  : ["term"],
              label_values : [$term],
              value        : $value
            }
          </str>
        </arr>
      </lst>
    </search>

  </rules>

</config>
----

|===
|Name|Description

|ping|Scrape <<ping.adoc#ping,Ping>> response.
|metrics|Scrape <<metrics-reporting.adoc#metrics-api,Metrics API>> response.
|collections|Scrape <<collections-api.adoc#collections-api,Collections API>> response.
|search|Scrape <<searching.adoc#searching,Search API>> response.
|*.query|Query parameter for each features. You can specify `collection`, `core`, `path`, and `params`.
|*.jsonQueries|JSON Query that is jq syntax. For more details, see https://stedolan.github.io/jq/manual/[https://stedolan.github.io/jq/manual/].
|===

jq query has to output JSON in the following format.

[source,json]
----
{
  name         : "solr_ping",
  type         : "GAUGE",
  help         : "See following URL: https://lucene.apache.org/solr/guide/ping.html",
  label_names  : ["base_url","core"],
  label_values : ["http://localhost:8983/solr","collection1"],
  value        : 1.0
}
----

It will be converted to the following exposition format.

[source,plain]
----
# TYPE solr_ping gauge
# HELP solr_ping See following URL: https://lucene.apache.org/solr/guide/ping.html
solr_ping{base_url="http://localhost:8983/solr",core="collection1"} 1.0
----

|===
|Name|Description

|name|The metric name to set. For more details, see https://prometheus.io/docs/practices/naming/[https://prometheus.io/docs/practices/naming/].
|type|The type of the metric, can be `COUNTER`, `GAUGE`, `SUMMARY`, `HISTOGRAM` or `UNTYPED`. For more detauils, see https://prometheus.io/docs/concepts/metric_types/[https://prometheus.io/docs/concepts/metric_types/].
|help|Help text for the metric.
|label_names|Label names for the metric. For more details, see https://prometheus.io/docs/practices/naming/[https://prometheus.io/docs/practices/naming/].
|label_values|Label values for the metric. For more details, see https://prometheus.io/docs/practices/naming/[https://prometheus.io/docs/practices/naming/].
|value|Value for the metric. Value must be set to Double type.
|===


== Prometheus Configuration

You need to specify the solr-exporter listen address into `scrape_configs` in `prometheus.yml`. See following example:

[source,plain]
----
scrape_configs:
  - job_name: 'solr'
    static_configs:
      - targets: ['localhost:9983']
----

When you apply the above settings to prometheus, it will start to pull Solr's metrics from solr-exporter.


== Grafana Dashboard

A Grafana sample dashboard is provided at the following JSON file.

`./contrib/prometheus-exporter/conf/grafana-solr-dashboard.json`

.Grafana Dashboard
image::images/monitoring-solr-with-prometheus-and-grafana/grafana-solr-dashboard.png[image,width=800]