MongoDB

Collect operation throughput, connection pool, replication lag, WiredTiger cache, and lock metrics from MongoDB using mongodb_exporter.

Pattern: mongodb_exporter → Prometheus scrape → xScaler remote_write

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Dashboard

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Prerequisites

• MongoDB 4.4 or later (replica set or standalone)
• A dedicated monitoring user
• Prometheus or Grafana Alloy
• xScaler tenant credentials

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Step 1 — Create a monitoring user

Connect to your MongoDB instance and run:

use admin
db.createUser({
  user: "xscaler_monitor",
  pwd: "strongpassword",
  roles: [
    { role: "clusterMonitor", db: "admin" },
    { role: "read", db: "local" }
  ]
})

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Step 2 — Run mongodb_exporter

docker run --rm -d \
  --name mongodb-exporter \
  -p 9216:9216 \
  percona/mongodb_exporter:0.40 \
  --mongodb.uri="mongodb://xscaler_monitor:strongpassword@localhost:27017" \
  --collect-all

Verify:

curl -s http://localhost:9216/metrics | grep mongodb_up
# mongodb_up 1

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Step 3 — Scrape and forward to xScaler

Prometheus

scrape_configs:
  - job_name: mongodb
    static_configs:
      - targets: ['localhost:9216']
        labels:
          instance: mongo-primary

remote_write:
  - url: https://euw1-01.m.xscalerlabs.com/api/v1/push
    authorization:
      credentials: <token>
    headers:
      X-Scope-OrgID: <tenant-id>

Grafana Alloy

prometheus.scrape "mongodb" {
  targets    = [{"__address__" = "localhost:9216"}]
  forward_to = [prometheus.remote_write.xscaler.receiver]
}

prometheus.remote_write "xscaler" {
  endpoint {
    url = "https://euw1-01.m.xscalerlabs.com/api/v1/push"
    authorization {
      type        = "Bearer"
      credentials = "<token>"
    }
    headers = { "X-Scope-OrgID" = "<tenant-id>" }
  }
}

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OpenTelemetry Collector

receivers:
  mongodb:
    hosts:
      - endpoint: localhost:27017
    username: xscaler_monitor
    password: strongpassword
    collection_interval: 15s
    tls:
      insecure: true

processors:
  memory_limiter:
    check_interval: 1s
    limit_mib: 256
  batch:
    timeout: 10s

exporters:
  otlphttp/xscaler:
    endpoint: https://euw1-01.m.xscalerlabs.com
    headers:
      Authorization: "Bearer <token>"
      X-Scope-OrgID: "<tenant-id>"

service:
  pipelines:
    metrics:
      receivers:  [mongodb]
      processors: [memory_limiter, batch]
      exporters:  [otlphttp/xscaler]

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Logs

Collect mongod log including queries, connections, and replica set events. Add the following to your Alloy config:

local.file_match "mongodb_logs" {
  path_targets = [{
    __address__ = "localhost",
    __path__    = "/var/log/mongodb/mongod.log",
    instance    = constants.hostname,
    job         = "integrations/mongodb",
  }]
}

loki.source.file "mongodb_logs" {
  targets    = local.file_match.mongodb_logs.targets
  forward_to = [loki.write.xscaler.receiver]
}

loki.write "xscaler" {
  endpoint {
    url = "https://euw1-01.l.xscalerlabs.com/api/v1/logs/push"

    http_client_config {
      authorization {
        type        = "Bearer"
        credentials = env("XSCALER_TOKEN")
      }
    }

    headers = { "X-Scope-OrgID" = env("XSCALER_TENANT_ID") }
  }
}

Key metrics

Metric	Description
mongodb_up	Exporter reachability (1 = up)
mongodb_connections_current	Current open connections
mongodb_connections_available	Remaining available connections
mongodb_op_counters_total	Operations by type (insert, query, update, delete)
mongodb_wiredtiger_cache_bytes_currently_in_cache	WiredTiger cache used
mongodb_wiredtiger_cache_max_bytes_configured	WiredTiger cache max size
mongodb_wiredtiger_cache_pages_evicted_from_cache_total	Cache page evictions
mongodb_repl_lag	Replication lag (seconds)
mongodb_mongod_global_lock_wait_time	Global lock wait time (µs)
mongodb_mongod_locks_time_locked_global_microseconds_total	Time spent holding global lock

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Useful PromQL queries

# Operation rate by type (inserts, queries, updates, deletes)
rate(mongodb_op_counters_total[5m])

# Connection usage %
mongodb_connections_current
/ (mongodb_connections_current + mongodb_connections_available) * 100

# WiredTiger cache usage %
mongodb_wiredtiger_cache_bytes_currently_in_cache
/ mongodb_wiredtiger_cache_max_bytes_configured * 100

# Replication lag (seconds)
mongodb_repl_lag

# Cache eviction rate (memory pressure indicator)
rate(mongodb_wiredtiger_cache_pages_evicted_from_cache_total[5m])

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Troubleshooting

mongodb_up 0

• Verify --mongodb.uri is reachable from the exporter container
• Ensure the monitoring user has clusterMonitor role: db.getUser("xscaler_monitor") in mongosh

No replication metrics

• mongodb_repl_lag is only present on replica set members, not standalone instances
• Confirm rs.status() returns a valid replica set state

Missing WiredTiger metrics

• WiredTiger is the default storage engine since MongoDB 3.2; if you're using MMAPv1, these metrics won't appear