[SOLR-15074] ClassCastException when repeating the same query param twice in Prometheus exporter config file

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 8.6.2
• Component/s: contrib - prometheus-exporter
• Assignee: Unassigned
• Reporter: Mathieu Marie
• Created: 07/Jan/21 14:50
• Updated: 13/Feb/21 00:07

Description

I am using the prometheus-exporter to monitor my service, and I wish to scale down the amount of data exchanged between solr and prometheus.
I can do that by updating the queries in the solr-exporter.xml file.
I wanted to use a query that look like :

http://localhost:8983/solr/admin/metrics?group=solr.node&regex=.*metrics.*requestTimes&property=p95_ms&property=count
{
  "responseHeader":{
    "status":0,
    "QTime":1},
  "metrics":{
    "solr.node":{
      "ADMIN./admin/metrics.distrib.requestTimes":{
        "count":0,
        "p95_ms":0.0},
      "ADMIN./admin/metrics.local.requestTimes":{
        "count":238,
        "p95_ms":1.984835},
      "ADMIN./admin/metrics.requestTimes":{
        "count":238,
        "p95_ms":1.995053},
      "QUERY./admin/metrics/collector.distrib.requestTimes":{
        "count":0,
        "p95_ms":0.0},
      "QUERY./admin/metrics/collector.local.requestTimes":{
        "count":0,
        "p95_ms":0.0},
      "QUERY./admin/metrics/collector.requestTimes":{
        "count":0,
        "p95_ms":0.0},
      "QUERY./admin/metrics/history.distrib.requestTimes":{
        "count":0,
        "p95_ms":0.0},
      "QUERY./admin/metrics/history.local.requestTimes":{
        "count":0,
        "p95_ms":0.0},
      "QUERY./admin/metrics/history.requestTimes":{
        "count":0,
        "p95_ms":0.0}}}}

In that query I repeated the param property to provide two values:
property=p95_ms&property=count

My config file look like that :

 

      <lst name="request">
        <lst name="query">
          <str name="path">/admin/metrics</str>
          <lst name="params">
            <str name="group">solr.core</str>
            <str name="regex">.*metrics.*requestTimes</str>
            <str name="property">count</str>
            <str name="property">p95_ms</str>
          </lst>
        </lst>
     ...
   </lst>

 

Then when the prometheus-exporter starts, it produces a ClassCastException.

Exception in thread "main" java.lang.RuntimeException: java.lang.ClassCastException: class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
 at org.apache.solr.prometheus.exporter.SolrExporter.loadMetricsConfiguration(SolrExporter.java:231)
 at org.apache.solr.prometheus.exporter.SolrExporter.main(SolrExporter.java:213)
Caused by: java.lang.ClassCastException: class java.util.ArrayList cannot be cast to class java.lang.String (java.util.ArrayList and java.lang.String are in module java.base of loader 'bootstrap')
 at org.apache.solr.prometheus.exporter.MetricsQuery.from(MetricsQuery.java:109)
 at org.apache.solr.prometheus.exporter.MetricsConfiguration.toMetricQueries(MetricsConfiguration.java:91)
 at org.apache.solr.prometheus.exporter.MetricsConfiguration.from(MetricsConfiguration.java:80)
 at org.apache.solr.prometheus.exporter.SolrExporter.loadMetricsConfiguration(SolrExporter.java:228)
 ... 1 more

 

This comes from a bad casting (obviously) in that code:

      NamedList query = (NamedList) request.get("query");
      NamedList queryParameters = (NamedList) query.get("params");
      String path = (String) query.get("path");
      String core = (String) query.get("core");
      String collection = (String) query.get("collection");
      List<String> jsonQueries = (ArrayList<String>) request.get("jsonQueries");

      ModifiableSolrParams params = new ModifiableSolrParams();
      if (queryParameters != null) {
        for (Map.Entry<String, String> entrySet : (Set<Map.Entry<String, String>>) queryParameters.asShallowMap().entrySet()) {
          params.add(entrySet.getKey(), entrySet.getValue());
        }
      }