Solr

Solr exposes Prometheus-format metrics natively at /solr/admin/metrics?wt=prometheus, so no exporter sidecar is needed. The OpenTelemetry Collector scrapes that endpoint with the prometheus receiver to collect 70+ metrics spanning request throughput and latency, searcher cache hit ratios, JVM heap and GC, indexing backlog, and index and disk capacity from Solr 7.x+. This guide configures the receiver, points it at a Solr node, and ships metrics to base14 Scout.

Prerequisites

Requirement	Minimum	Recommended
Solr	7.x	10.0
OTel Collector Contrib	0.90.0	latest
base14 Scout	Any	-

Before starting:

• Solr's HTTP port (8983) must be reachable from the host running the Collector.
• The /solr/admin/metrics endpoint is enabled by default.
• A Scout account and OTLP endpoint.
• OTel Collector installed - see Docker Compose Setup.

What You'll Monitor

Metrics are grouped into three tiers by how you use them. Scrape Core always, alert on Operational, and reach for Diagnostic during an incident or capacity review.

Core - is it up and serving

Metric	What it tells you
up	Scrape succeeded - the metrics endpoint is reachable and monitoring itself is alive.
solr_core_requests_total	Request throughput per handler and core - the headline KPI for "is Solr answering queries".

Operational - what to alert on

Group	Metrics	What it tells you
Request latency	solr_core_requests_times_milliseconds, solr_node_requests_times_milliseconds	Per-handler and node-level request latency (count / sum / quantiles).
Node throughput	solr_node_requests_total	Node-level request count alongside the per-core total.
Searcher cache	solr_core_indexsearcher_cache_lookups_total, solr_core_indexsearcher_cache_ops_total	Cache lookups and hits / inserts / evictions by op - the inputs to hit ratio.
JVM memory	jvm_memory_used_bytes, jvm_memory_limit_bytes	Heap / non-heap in use against the ceiling; the saturation signal for OOM and GC risk.
GC	jvm_gc_duration_seconds	Stop-the-world pause time; rising pauses hurt query latency.
Indexing backlog	solr_core_update_docs_pending_commit	Docs added but not yet committed - a climbing value means commits are stalled.
Capacity	solr_core_index_size_megabytes, solr_disk_space_megabytes, solr_cores_loaded	On-disk index size per core, free disk for Solr data, and the count of loaded cores.

Hit ratio is not a single metric - derive it as solr_core_indexsearcher_cache_ops_total{...hits} over solr_core_indexsearcher_cache_lookups_total.

Diagnostic - for investigation and tuning

Higher cardinality; enable on demand. In production you can drop this tier with metric_relabel_configs and keep Core + Operational.

Group	Metrics	When you reach for it
Searcher caches	solr_core_indexsearcher_cache_size, _cache_ram_used_bytes, _cache_warmup_time_milliseconds, _live_docs_cache_total, _termstats_cache, solr_core_field_cache_entries, _field_cache_size_bytes	Per-cache sizing, RAM, and warmup cost when tuning cache configuration.
Index / searcher detail	solr_core_indexsearcher_index_docs, _index_num_docs, _index_version, _index_commit_size_megabytes, _open_time_milliseconds, _open_warmup_time_milliseconds, solr_core_segments, solr_core_searcher_new_total, solr_core_indexwriter_flushes_total, solr_core_disk_space_megabytes, solr_core_ref_count	Segment counts, searcher reopens, and index internals during merge or commit investigation.
Update / transaction log	solr_core_update_auto_commits_total, _commit_ops_total, _commit_stats, _committed_ops_total, _cumulative_ops, _log_buffered_ops, _log_replay_logs_remaining, _log_size_remaining_bytes, _log_state, _submitted_ops_total	Commit cadence and tlog replay state when indexing or recovery misbehaves.
Replication	solr_core_replication_index_generation, _index_size_megabytes, _index_version, _is_enabled, _is_follower, _is_leader	Leader / follower role and replication progress (read their not-configured defaults on a standalone node).
Executors / thread pools	solr_core_executor_thread_pool_size, _executor_thread_pool_tasks, solr_node_executor_task_times_milliseconds, _executor_tasks_running, _executor_tasks_total, _executor_thread_pool_size, _executor_thread_pool_tasks	Thread-pool depth and task timing under concurrency.
JVM detail	jvm_buffer_*, jvm_class_*, jvm_cpu_*, jvm_memory_allocation_bytes, _memory_committed_bytes, _memory_init_bytes, _memory_used_after_last_gc_bytes, jvm_network_*, jvm_system_cpu_utilization_ratio, jvm_thread_count	The full JVM breakdown - buffers, class loading, CPU, allocation, and threads - for deep JVM tuning.

Full metric reference: run curl -s 'http://localhost:8983/solr/admin/metrics?wt=prometheus' against your Solr instance, or see the Solr metrics reporting documentation.

SolrCloud-only series (overseer, ZooKeeper, shard / replica state) do not appear on a standalone node, and the replication series read their not-configured defaults until replication is set up.

Key Alerts to Configure

Threshold guidance for the most useful Operational-tier series. Tune to your workload; these are starting points.

Metric	Warning	Critical	Why it matters
solr_core_requests_times_milliseconds (p95)	Rising vs baseline	Sustained regression	Query slowdown; check cache hit ratio, GC, and slow queries.
cache_ops_total{...hits} / cache_lookups_total	Hit ratio falling	Sharply low	Cache too small or churning; tune cache sizes / autowarm.
jvm_memory_used_bytes / jvm_memory_limit_bytes	> 80% of limit	Near limit	OOM and long-GC risk; raise heap or reduce cache / field load.
rate(jvm_gc_duration_seconds)	Rising	Sustained high	Stop-the-world pauses hurting latency; tune heap / GC.
solr_core_update_docs_pending_commit	Climbing without commit	Not draining	Commits stalled; check commit settings and indexing throughput.
solr_disk_space_megabytes (free)	Trending down	< 10% of volume	Plan storage before the volume fills as index_size_megabytes grows.

Access Setup

Solr serves Prometheus-format metrics natively - there is no exporter to run. The metrics live at /solr/admin/metrics and the wt=prometheus query parameter selects the Prometheus rendering.

Verify the endpoint is reachable:

Verify access

# Check Solr status
curl -s http://localhost:8983/solr/admin/info/system | head -20

# List cores
curl -s http://localhost:8983/solr/admin/cores

# Verify Prometheus metrics endpoint
curl -s 'http://localhost:8983/solr/admin/metrics?wt=prometheus' | head -20

No authentication is required by default. Clusters with Basic Authentication enabled need credentials on the scrape - see Authentication below.

The Collector's prometheus receiver must override the default /metrics path with metrics_path: /solr/admin/metrics and pass params: { wt: [prometheus] }. Both are set in the Configuration section.

Configuration

config/otel-collector.yaml

receivers:
  prometheus:
    config:
      scrape_configs:
        - job_name: solr
          scrape_interval: 30s
          metrics_path: /solr/admin/metrics   # Solr's endpoint, not the default /metrics
          params:
            wt: [prometheus]                   # Select Prometheus rendering
          static_configs:
            - targets:
                - ${env:SOLR_HOST}:8983

processors:
  resource:
    attributes:
      - key: environment
        value: ${env:ENVIRONMENT}
        action: upsert
      - key: service.name
        value: ${env:SERVICE_NAME}
        action: upsert

  batch:
    timeout: 10s
    send_batch_size: 1024

exporters:
  otlphttp/b14:
    endpoint: ${env:OTEL_EXPORTER_OTLP_ENDPOINT}
    tls:
      insecure_skip_verify: true        # Set to false with TLS in production

service:
  pipelines:
    metrics:
      receivers: [prometheus]
      processors: [resource, batch]
      exporters: [otlphttp/b14]

To control metric volume in production, drop the Diagnostic tier with a metric_relabel_configs block on the scrape config while keeping the Core and Operational series.

Environment Variables

.env

SOLR_HOST=localhost
ENVIRONMENT=your_environment
SERVICE_NAME=your_service_name
OTEL_EXPORTER_OTLP_ENDPOINT=https://<your-tenant>.base14.io

Authentication

For Solr clusters with Basic Authentication enabled, add basic_auth to the scrape config:

config/otel-collector.yaml (auth)

receivers:
  prometheus:
    config:
      scrape_configs:
        - job_name: solr
          metrics_path: /solr/admin/metrics
          params:
            wt: [prometheus]
          basic_auth:
            username: ${env:SOLR_USERNAME}
            password: ${env:SOLR_PASSWORD}
          static_configs:
            - targets:
                - ${env:SOLR_HOST}:8983

Filtering Metrics

To collect only specific metric groups, use Solr's group parameter:

config/otel-collector.yaml (filter)

receivers:
  prometheus:
    config:
      scrape_configs:
        - job_name: solr
          metrics_path: /solr/admin/metrics
          params:
            wt: [prometheus]
            group: [jvm, node, core]   # Limit to selected metric groups
          static_configs:
            - targets:
                - ${env:SOLR_HOST}:8983

Available groups: jvm, jetty, node, core, overseer.

Verify the Setup

Start the Collector and check for metrics within 60 seconds:

Verify metrics collection

# Check Collector logs for scraped Solr metrics (grep the metric prefix)
docker logs otel-collector 2>&1 | grep -i "solr_core"

# Confirm the endpoint is serving Prometheus-format metrics
curl -s 'http://localhost:8983/solr/admin/metrics?wt=prometheus' \
  | grep solr_core_requests_total

# Generate request and index traffic so the series move
curl -s 'http://localhost:8983/solr/demo/select?q=*:*' > /dev/null

Troubleshooting

Connection refused on port 8983

Cause: The Collector cannot reach Solr at the configured address.

Fix:

1. Verify Solr is running: docker ps | grep solr or systemctl status solr.
2. Confirm Solr is listening: curl http://localhost:8983/solr/.
3. Check firewall rules if the Collector runs on a separate host.

Metrics endpoint returns JSON instead of Prometheus format

Cause: The wt=prometheus parameter is missing from the scrape config, so Solr falls back to JSON, which the prometheus receiver cannot parse.

Fix:

1. Ensure params: { wt: [prometheus] } is set on the scrape job.
2. Confirm metrics_path is /solr/admin/metrics, not the default /metrics.
3. Verify with curl 'http://localhost:8983/solr/admin/metrics?wt=prometheus'.

Queries are slow or latency is climbing

Cause: A low cache hit ratio, JVM heap pressure, or GC pauses.

Look at: the searcher-cache Diagnostic series - solr_core_indexsearcher_cache_size, _cache_ram_used_bytes, and _cache_warmup_time_milliseconds - alongside jvm_memory_used_bytes against jvm_memory_limit_bytes and the jvm_gc_duration_seconds rate. A hit ratio falling while warmup time climbs points at undersized or churning caches; heap near the limit with rising GC points at memory pressure.

Fix:

1. Tune cache sizes and autowarm counts if the hit ratio is low.
2. Raise heap or reduce cache / field load if jvm_memory_used_bytes sits near jvm_memory_limit_bytes.

Indexing backlog grows and commits stall

Cause: Commits are not keeping up with indexing, or the transaction log is replaying.

Look at: the update / tlog Diagnostic series - solr_core_update_commit_ops_total, solr_core_update_auto_commits_total, and solr_core_update_log_replay_logs_remaining - against the Operational solr_core_update_docs_pending_commit. A pending count that climbs while commit ops stay flat means commits are stalled; non-zero replay logs means the node is still recovering its tlog.

Fix:

1. Review autoCommit / autoSoftCommit settings and commit cadence.
2. Throttle indexing throughput or add capacity if commits cannot keep up.

Core-level metrics missing

Cause: Core metrics (solr_core_*) only appear when at least one core is loaded.

Fix:

1. Create a core: curl 'http://localhost:8983/solr/admin/cores?action=CREATE&name=demo&configSet=_default'.
2. Verify cores exist: curl http://localhost:8983/solr/admin/cores.
3. Check solr_cores_loaded reflects the expected count.

No metrics appearing in Scout

Cause: Metrics are collected but not exported.

Fix:

1. Check Collector logs for export errors: docker logs otel-collector.
2. Verify OTEL_EXPORTER_OTLP_ENDPOINT is set correctly.
3. Confirm the pipeline includes both the receiver and the exporter.

FAQ

Does this work with Solr running in Kubernetes?

Yes. Set targets to the Solr pod or service DNS (e.g., solr-0.solr.default.svc.cluster.local:8983) and keep the metrics_path and params overrides. The Collector can run as a sidecar or a DaemonSet.

How do I monitor a SolrCloud cluster?

Add every node endpoint to the scrape config. Each node is scraped independently and identified by its instance label:

config/otel-collector.yaml (multi-node)

receivers:
  prometheus:
    config:
      scrape_configs:
        - job_name: solr
          metrics_path: /solr/admin/metrics
          params:
            wt: [prometheus]
          static_configs:
            - targets:
                - solr-1:8983
                - solr-2:8983
                - solr-3:8983

What is the difference between node and core metrics?

Node metrics (solr_node_*) cover the whole instance - aggregate request counts, latency, and executor pools. Core metrics (solr_core_*) are per-core and include request throughput, searcher caches, index size, and update-handler stats. Core metrics only appear once a core is loaded.

Why are overseer and replication metrics empty?

Overseer metrics only appear in SolrCloud mode on the elected overseer node, so a standalone instance does not emit them. The solr_core_replication_* series read their not-configured defaults (for example solr_core_replication_is_enabled) until replication is actually set up.

Why is the cache hit ratio not a single metric?

Solr exposes the inputs, not the ratio. Derive it as solr_core_indexsearcher_cache_ops_total{...hits} over solr_core_indexsearcher_cache_lookups_total and chart or alert on the quotient.

Related Guides

• OTel Collector Configuration - Advanced collector configuration.
• Docker Compose Setup - Run the Collector locally.
• Kubernetes Helm Setup - Production deployment.
• Creating Alerts - Alert on Solr metrics.
• Elasticsearch Monitoring - Another search engine you may run alongside Solr.
• Redis Monitoring - A common caching layer in front of search.

What's Next?

• Create Dashboards: Explore pre-built dashboards or build your own. See Create Your First Dashboard.
• Monitor More Components: Add monitoring for Elasticsearch, Redis, and other components.
• Fine-tune Collection: Drop the Diagnostic tier in production with metric_relabel_configs to control volume; keep it available for incident investigation.