dbpulse 0.8.1

command line tool to monitor that database is available for read & write
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dbpulse 🩺

A lightweight database health monitoring tool that continuously tests database availability for read and write operations. It exposes Prometheus-compatible metrics for monitoring database health, performance, and operational metrics.

Overview

Like a paramedic checking for a pulse, dbpulse performs quick vital sign checks on your database. It goes beyond simple connection tests by performing real database operations (INSERT, SELECT, UPDATE, DELETE, transaction rollback) at regular intervals to verify that your database is truly alive and accepting writes, not just accepting connections.

Quick Pulse Check: Is the database responsive and healthy? ✅ Vital Signs: Latency, errors, read-only status, replication lag 📊 Emergency Indicators: Blocking queries, locked tables, connectivity issues 🚨

This is particularly useful for:

  • Galera Clusters - Detecting HALT/LOCK cases where DDL statements stall the cluster or flow-control prevents COMMITS/WRITES
  • Read-Only Detection - Identifying when databases enter read-only mode (replicas, maintenance, failover scenarios)
  • Replication Monitoring - Tracking replication lag on replica databases
  • Lock Detection - Identifying blocking queries that prevent other operations
  • Performance Monitoring - Measuring query latency, connection times, and operation throughput

The tool protects itself from hanging on locked tables using configurable timeouts (5s statement timeout, 2s lock timeout), ensuring the health probe remains responsive.

Quick Start

# PostgreSQL
dbpulse --dsn "postgres://user:password@tcp(localhost:5432)/mydb"

# MySQL/MariaDB
dbpulse --dsn "mysql://user:password@tcp(localhost:3306)/mydb"

# With custom interval and range
dbpulse --dsn "postgres://user:pass@tcp(db.example.com:5432)/prod" \
  --interval 60 \
  --range 1000 \
  --port 9300

Access metrics at http://localhost:9300/metrics

Usage

Command-Line Options

dbpulse [OPTIONS] --dsn <DSN>

Required Options

Option Environment Variable Description
-d, --dsn <DSN> DBPULSE_DSN Database connection string (see DSN Format below)

Optional Settings

Option Environment Variable Default Description
-i, --interval <SECONDS> DBPULSE_INTERVAL 30 Seconds between health checks
-p, --port <PORT> DBPULSE_PORT 9300 HTTP port for /metrics endpoint
-l, --listen <IP> DBPULSE_LISTEN [::] IP address to bind to (supports IPv4 and IPv6)
-r, --range <RANGE> DBPULSE_RANGE 100 Upper limit for random ID generation (prevents conflicts in multi-instance setups)
N/A DBPULSE_TLS_CERT_CACHE_TTL 3600 TLS certificate cache TTL in seconds (0 to disable caching)

DSN Format

The Data Source Name (DSN) follows this format:

<driver>://<user>:<password>@tcp(<host>:<port>)/<database>[?param1=value1&param2=value2]

Supported drivers: postgres, mysql

Basic Examples

# PostgreSQL
postgres://dbuser:secret@tcp(localhost:5432)/production

# MySQL/MariaDB
mysql://root:password@tcp(db.example.com:3306)/myapp

# With custom port
postgres://admin:pass@tcp(10.0.1.50:5433)/metrics_db

# Unix socket (PostgreSQL)
postgres://user:pass@unix(/var/run/postgresql)/mydb

TLS/SSL Parameters

Configure TLS directly in the DSN query string:

Parameter Values Description
sslmode disable, require, verify-ca, verify-full TLS mode (default: disable)
sslrootcert or sslca /path/to/ca.crt CA certificate for server verification
sslcert /path/to/client.crt Client certificate (mutual TLS)
sslkey /path/to/client.key Client private key (mutual TLS)

TLS Mode Details:

  • disable - No encryption (plaintext)
  • require - Encrypted connection, no certificate verification
  • verify-ca - Verify server certificate against CA
  • verify-full - Verify certificate and hostname match

TLS Examples

# PostgreSQL with TLS required
dbpulse --dsn "postgres://user:pass@tcp(db.example.com:5432)/prod?sslmode=require"

# PostgreSQL with full certificate verification
dbpulse --dsn "postgres://user:pass@tcp(db.example.com:5432)/prod?sslmode=verify-full&sslrootcert=/etc/ssl/certs/ca.crt"

# MySQL with CA verification
dbpulse --dsn "mysql://user:pass@tcp(db.example.com:3306)/prod?sslmode=verify-ca&sslca=/etc/ssl/ca.crt"

# Mutual TLS (client certificates)
dbpulse --dsn "postgres://user:pass@tcp(db.example.com:5432)/prod?sslmode=verify-full&sslrootcert=/etc/ssl/ca.crt&sslcert=/etc/ssl/client.crt&sslkey=/etc/ssl/client.key"

Environment Variables

All options can be set via environment variables:

export DBPULSE_DSN="postgres://user:pass@tcp(localhost:5432)/mydb"
export DBPULSE_INTERVAL=60
export DBPULSE_PORT=9300
export DBPULSE_RANGE=1000
export DBPULSE_TLS_CERT_CACHE_TTL=3600  # Cache TLS certificate for 1 hour (default)

dbpulse  # Uses environment variables

TLS Certificate Caching Examples:

# Production: Check certificate every 30 minutes
export DBPULSE_TLS_CERT_CACHE_TTL=1800

# Stable environments: Check once per day
export DBPULSE_TLS_CERT_CACHE_TTL=86400

# Testing: Disable cache (probe every health check)
export DBPULSE_TLS_CERT_CACHE_TTL=0

# Default: Check once per hour (if not set)
# No need to set, 3600 is automatic

Complete Examples

Production PostgreSQL with TLS:

dbpulse \
  --dsn "postgres://monitor:secret@tcp(prod-db.example.com:5432)/app?sslmode=verify-full&sslrootcert=/etc/ssl/certs/ca-bundle.crt" \
  --interval 30 \
  --port 9300 \
  --range 1000

MySQL Cluster Monitoring:

dbpulse \
  --dsn "mysql://healthcheck:pass@tcp(galera-lb.internal:3306)/monitoring" \
  --interval 15 \
  --listen "0.0.0.0" \
  --port 8080

Development Setup:

dbpulse --dsn "postgres://postgres:postgres@tcp(localhost:5432)/test" -i 10 -r 50

How It Works

dbpulse performs database health checks in a simple, repeating cycle:

1. Configuration from DSN

All TLS/SSL settings come from the DSN query parameters (no separate flags):

# TLS configuration is in the DSN string
--dsn "postgres://user:pass@host:5432/db?sslmode=verify-full&sslrootcert=/etc/ssl/ca.crt"

The DSN parser extracts sslmode, sslrootcert, sslcert, and sslkey parameters into a TlsConfig struct used for both database and certificate connections.

2. Health Check Cycle

Every interval (default: 30 seconds), dbpulse performs health checks:

Connection #1 - Database Operations (SQLx):

  • Connects with proper TLS verification based on sslmode
  • Executes write test (INSERT/UPDATE with unique UUID)
  • Verifies read operation (SELECT to confirm data)
  • Collects metrics (table size, replication lag, blocking queries)
  • Queries TLS info from database (pg_stat_ssl or SHOW STATUS LIKE 'Ssl%')

Connection #2 - Certificate Inspection (Probe) - CACHED:

  • Opens separate TLS connection to database server
  • Performs STARTTLS negotiation (protocol-specific)
  • Extracts certificate metadata (subject, issuer, expiry date)
  • Closes immediately (no database queries)
  • Cached by default: Probe runs once per hour (configurable via DBPULSE_TLS_CERT_CACHE_TTL)
  • Cache key: host:port combination
  • Reduces from 120 probes/hour to 1 probe/hour with default settings

Both connections use the same TLS configuration from the DSN. The probe connection uses a NoVerifier to inspect certificates without validation (actual security happens in Connection #1).

Why two connections? SQLx doesn't expose peer certificates from its internal TLS stream, so certificate metadata must be extracted separately.

3. Certificate Caching

Default behavior (1 hour cache):

  • First health check: Both Connection #1 and #2 execute (~100-150ms)
  • Subsequent checks (for 1 hour): Only Connection #1 executes (~50-80ms)
  • After 1 hour: Cache expires, Connection #2 runs again

Customizing cache TTL:

# Check certificate every 30 minutes
export DBPULSE_TLS_CERT_CACHE_TTL=1800

# Check certificate once per day
export DBPULSE_TLS_CERT_CACHE_TTL=86400

# Disable caching (probe every iteration - not recommended)
export DBPULSE_TLS_CERT_CACHE_TTL=0

Performance impact:

  • Default (30s interval, 1h cache): 95% reduction in TLS probe connections
  • Memory overhead: ~200 bytes per cached certificate
  • Thread-safe: Uses Arc<RwLock<HashMap>> for concurrent access

4. Metrics Export

Results are merged and exposed as Prometheus metrics on /metrics:

  • Health status, latency, error rates
  • TLS version, cipher suite (from Connection #1)
  • Certificate subject, issuer, expiry days (from Connection #2, cached)

What It Monitors

Health Check Operations (The Pulse Check 🩺)

Every interval, dbpulse performs a quick vital signs check:

  1. Connection Test ⚡ - Establishes database connection with timeouts
  2. Version Check 🔍 - Retrieves database version
  3. Read-Only Detection 🔒 - Checks if database accepts writes
  4. Write Operation ✍️ - INSERT or UPDATE with unique ID and UUID
  5. Read Verification ✅ - SELECT to verify written data matches
  6. Transaction Test 🔄 - Tests rollback capability
  7. Cleanup 🧹 - Deletes old records (keeps table size bounded)

Timeout Protection:

  • PostgreSQL: 5s statement timeout, 2s lock timeout
  • MySQL/MariaDB: 5s max execution time, 2s lock wait timeout

These timeouts prevent the health probe from hanging on locked tables.

Operational Metrics (Best-effort)

In addition to health checks, dbpulse collects:

  • Replication Lag - For replica databases only (PostgreSQL: pg_last_xact_replay_timestamp(), MySQL: SHOW REPLICA STATUS)
  • Blocking Queries - Count of queries currently blocking others
  • Database Size - Total database size in bytes
  • Table Size - Monitoring table size and row count
  • Connection Duration - How long connections are held open
  • TLS Handshake Time - When TLS is enabled

All operational metrics use if let Ok(...) pattern - they never fail the health check.

Metrics

dbpulse exposes comprehensive Prometheus-compatible metrics on the /metrics endpoint.

Core Health Metrics

Metric Type Description
dbpulse_pulse Gauge Binary health status (1=healthy, 0=unhealthy)
dbpulse_runtime Histogram Total health check duration (seconds)
dbpulse_iterations_total Counter Total checks by status (success/error)
dbpulse_last_success_timestamp_seconds Gauge Unix timestamp of last successful check
dbpulse_database_readonly Gauge Read-only mode indicator (1=read-only, 0=read-write)

Performance Metrics

Metric Type Description
dbpulse_operation_duration_seconds Histogram Duration by operation (connect, insert, select, etc.)
dbpulse_connection_duration_seconds Histogram How long connections are held open
dbpulse_connections_active Gauge Currently active database connections

Database Operations

Metric Type Description
dbpulse_rows_affected_total Counter Total rows affected by operation type (insert, delete)
dbpulse_table_size_bytes Gauge Monitoring table size in bytes
dbpulse_table_rows Gauge Approximate row count in monitoring table
dbpulse_database_size_bytes Gauge Total database size in bytes

Replication & Blocking

Metric Type Description
dbpulse_replication_lag_seconds Histogram Replication lag for replica databases
dbpulse_blocking_queries Gauge Number of queries currently blocking others

Error Tracking

Metric Type Description
dbpulse_errors_total Counter Total errors by type (authentication, timeout, connection, transaction, query)
dbpulse_panics_recovered_total Counter Total panics recovered from

TLS/SSL Metrics

Metric Type Description
dbpulse_tls_handshake_duration_seconds Histogram TLS handshake duration
dbpulse_tls_connection_errors_total Counter TLS-specific connection errors
dbpulse_tls_info Gauge TLS version and cipher suite (labels: version, cipher)
dbpulse_tls_cert_expiry_days Gauge Days until TLS certificate expiration (negative if expired)

For complete documentation, PromQL examples, and alert rules, see grafana/README.md.

Key Metrics Examples

# Database health
dbpulse_pulse

# Success rate
rate(dbpulse_iterations_total{status="success"}[5m]) /
  rate(dbpulse_iterations_total[5m]) * 100

# P99 latency
histogram_quantile(0.99, rate(dbpulse_runtime_bucket[5m]))

# Error rate by type
rate(dbpulse_errors_total[5m])

# Connection time
rate(dbpulse_operation_duration_seconds_sum{operation="connect"}[5m]) /
  rate(dbpulse_operation_duration_seconds_count{operation="connect"}[5m])

# TLS certificate expiry (days remaining)
dbpulse_tls_cert_expiry_days

# Certificates expiring within 30 days
dbpulse_tls_cert_expiry_days < 30 and dbpulse_tls_cert_expiry_days > 0

Example Alerts

- alert: DatabaseDown
  expr: dbpulse_pulse == 0
  for: 2m
  labels:
    severity: critical

- alert: HighErrorRate
  expr: rate(dbpulse_errors_total[5m]) > 0.1
  for: 5m
  labels:
    severity: warning

- alert: NoRecentSuccess
  expr: time() - dbpulse_last_success_timestamp_seconds > 300
  for: 1m
  labels:
    severity: critical

- alert: TLSCertificateExpiringSoon
  expr: dbpulse_tls_cert_expiry_days < 30 and dbpulse_tls_cert_expiry_days > 0
  for: 1h
  labels:
    severity: warning
  annotations:
    summary: "TLS certificate expires in {{ $value }} days"
    description: "Database {{ $labels.database }} TLS certificate will expire soon"

- alert: TLSCertificateExpired
  expr: dbpulse_tls_cert_expiry_days < 0
  for: 5m
  labels:
    severity: critical
  annotations:
    summary: "TLS certificate has expired"
    description: "Database {{ $labels.database }} TLS certificate expired {{ $value | abs }} days ago"

Database Permissions

The monitoring user needs these permissions:

PostgreSQL:

-- Create monitoring user
CREATE USER dbpulse_monitor WITH PASSWORD 'secret';

-- Grant database access
GRANT CONNECT ON DATABASE mydb TO dbpulse_monitor;
GRANT CREATE ON DATABASE mydb TO dbpulse_monitor;  -- Optional: allows auto-creation

-- Grant schema access
GRANT USAGE ON SCHEMA public TO dbpulse_monitor;
GRANT CREATE ON SCHEMA public TO dbpulse_monitor;

-- Allow table creation and operations
GRANT CREATE ON SCHEMA public TO dbpulse_monitor;
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT ALL ON TABLES TO dbpulse_monitor;

MySQL/MariaDB:

-- Create monitoring user
CREATE USER 'dbpulse_monitor'@'%' IDENTIFIED BY 'secret';

-- Grant necessary permissions
GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP ON mydb.* TO 'dbpulse_monitor'@'%';
GRANT REPLICATION CLIENT ON *.* TO 'dbpulse_monitor'@'%';  -- For replication lag monitoring
GRANT PROCESS ON *.* TO 'dbpulse_monitor'@'%';  -- For blocking query detection

FLUSH PRIVILEGES;

Minimal Permissions (read-only monitoring): If the dbpulse_rw table already exists, only these are needed:

-- PostgreSQL
GRANT SELECT, INSERT, UPDATE, DELETE ON TABLE dbpulse_rw TO dbpulse_monitor;

-- MySQL
GRANT SELECT, INSERT, UPDATE, DELETE ON mydb.dbpulse_rw TO 'dbpulse_monitor'@'%';

Note: dbpulse will attempt to create the database if it doesn't exist (requires appropriate permissions).

Monitoring Table

dbpulse creates and manages a table named dbpulse_rw (or custom name if using multiple instances) with this schema:

PostgreSQL:

CREATE TABLE IF NOT EXISTS dbpulse_rw (
    id INT NOT NULL,
    t1 BIGINT NOT NULL,
    t2 TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    uuid UUID,
    PRIMARY KEY(id)
);
CREATE UNIQUE INDEX IF NOT EXISTS idx_uuid ON dbpulse_rw(uuid);
CREATE INDEX IF NOT EXISTS idx_t2 ON dbpulse_rw(t2);

MySQL/MariaDB:

CREATE TABLE IF NOT EXISTS dbpulse_rw (
    id INT NOT NULL,
    t1 BIGINT NOT NULL,
    t2 TIMESTAMP(6) NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    uuid CHAR(36) CHARACTER SET ascii,
    PRIMARY KEY(id),
    UNIQUE KEY(uuid),
    INDEX idx_t2 (t2)
) ENGINE=InnoDB;

Table Cleanup

The table is automatically maintained:

  • Hourly cleanup: Records older than 1 hour are deleted (LIMIT 10000 per check)
  • Periodic drop: Table is completely dropped and recreated every hour (when row count < 100k and at minute 0)
  • Bounded growth: Table size remains small even with frequent checks

Custom Table Names

Use different table names for multiple monitoring instances:

# Instance 1
dbpulse --dsn "postgres://user:pass@tcp(db:5432)/prod" --range 1000

# Instance 2 (different range = different table name)
dbpulse --dsn "postgres://user:pass@tcp(db:5432)/prod" --range 2000

Deployment

Container Image

Container images are automatically published to GitHub Container Registry on each release.

Pull the image:

podman pull ghcr.io/nbari/dbpulse:latest

Run with Docker/Podman:

# PostgreSQL
podman run -d \
  --name dbpulse \
  -p 9300:9300 \
  -e DBPULSE_DSN="postgres://user:password@host.docker.internal:5432/mydb" \
  ghcr.io/nbari/dbpulse:latest

# MySQL/MariaDB with TLS
docker run -d \
  --name dbpulse \
  -p 9300:9300 \
  -v /etc/ssl/certs:/etc/ssl/certs:ro \
  -e DBPULSE_DSN="mysql://user:pass@tcp(db.example.com:3306)/prod?sslmode=verify-ca&sslca=/etc/ssl/certs/ca.crt" \
  -e DBPULSE_INTERVAL=60 \
  ghcr.io/nbari/dbpulse:latest

Multi-architecture support:

  • linux/amd64 - x86_64 architecture
  • linux/arm64 - ARM64 architecture (AWS Graviton, Apple Silicon, Raspberry Pi)

Systemd Service

[Unit]
Description=Database Pulse Monitor
After=network.target

[Service]
Type=simple
User=dbpulse
Group=dbpulse
Environment="DBPULSE_DSN=postgres://monitor:secret@tcp(localhost:5432)/prod?sslmode=verify-full&sslrootcert=/etc/ssl/certs/ca.crt"
Environment="DBPULSE_INTERVAL=30"
Environment="DBPULSE_PORT=9300"
ExecStart=/usr/local/bin/dbpulse
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

Save to /etc/systemd/system/dbpulse.service, then:

sudo systemctl daemon-reload
sudo systemctl enable dbpulse
sudo systemctl start dbpulse
sudo systemctl status dbpulse

Development

Testing

Run all tests (unit, integration, TLS):

just test

Run individual test suites:

just unit-test         # Unit tests only
just test-integration  # Integration tests (non-TLS)
just test-tls          # TLS integration tests

For detailed documentation, see: