tutorial

How to Monitor KeyDB with Vigilmon (HTTP + TCP + Alerts)

KeyDB is a high-performance, multithreaded fork of Redis that delivers significantly higher throughput on multi-core hardware while remaining compatible with...

KeyDB is a high-performance, multithreaded fork of Redis that delivers significantly higher throughput on multi-core hardware while remaining compatible with the Redis protocol and client ecosystem. Teams choose KeyDB when they've hit Redis's single-threaded throughput ceiling — but running KeyDB in production means you need the same operational discipline as Redis, including robust external monitoring.

In this tutorial you'll set up comprehensive uptime monitoring for KeyDB using Vigilmon — free tier, no credit card required.

Why KeyDB needs external monitoring

KeyDB's multithreaded architecture changes some failure modes compared to Redis:

  • Thread contention crashes — under extreme load, KeyDB can hit thread synchronization bugs that cause silent crashes or partial availability; the process exits cleanly but your cache becomes unavailable
  • Active replication conflicts — KeyDB's active-active replication can produce split-brain conditions where both nodes accept writes but diverge; redis-cli ping returns PONG on both but your data is inconsistent
  • Port binding failures on restart — a crashed KeyDB process leaves a socket in TIME_WAIT; the restart succeeds internally but the port isn't reachable
  • Maxmemory eviction loops — KeyDB evicts keys faster than your app writes them, causing thundering herd patterns where cache misses hammer your database; the KeyDB process is healthy but latency spikes to seconds
  • TLS termination failures — if you run KeyDB with TLS, a certificate rotation can break the TLS handshake while the underlying TCP port remains open

None of these are visible from redis-cli ping alone. External HTTP and TCP monitoring from outside the machine gives you an independent view of what clients actually experience.

What you'll need

  • A running KeyDB server (single instance, replica, or active-active cluster)
  • Network access to KeyDB from outside the host (TCP port, typically 6379)
  • A free Vigilmon account (sign up takes 30 seconds)

Step 1: Install and configure KeyDB

If you're starting fresh, install KeyDB on Ubuntu/Debian:

# Add the KeyDB repository
curl -fsSL https://download.keydb.dev/pkg/open_source/gpg | \
  sudo gpg --dearmor -o /usr/share/keyrings/keydb.gpg

echo "deb [signed-by=/usr/share/keyrings/keydb.gpg] \
  https://download.keydb.dev/pkg/open_source/deb $(lsb_release -cs) main" | \
  sudo tee /etc/apt/sources.list.d/keydb.list

sudo apt update && sudo apt install -y keydb

Or via Docker:

docker run -d \
  --name keydb \
  -p 6379:6379 \
  -v keydb-data:/data \
  eqalpha/keydb:latest \
  keydb-server \
    --server-threads 4 \
    --active-replication yes \
    --bind 0.0.0.0 \
    --protected-mode no \
    --maxmemory 2gb \
    --maxmemory-policy allkeys-lru \
    --save 900 1 \
    --save 300 10 \
    --appendonly yes

Verify it's running:

redis-cli -p 6379 ping
# PONG

redis-cli -p 6379 info server | grep -E "keydb_version|tcp_port"
# keydb_version:6.3.4
# tcp_port:6379

Step 2: Deploy an HTTP health endpoint

KeyDB speaks the Redis protocol over TCP — not HTTP. To enable Vigilmon's HTTP monitoring, deploy a lightweight health proxy alongside KeyDB. This proxy runs a liveness check against KeyDB and exposes the result as an HTTP endpoint.

Here's a minimal Node.js health server:

// keydb-health.js
const http = require('http');
const { createClient } = require('redis');

const client = createClient({
  socket: {
    host: process.env.KEYDB_HOST || '127.0.0.1',
    port: parseInt(process.env.KEYDB_PORT || '6379'),
    connectTimeout: 3000,
  },
  password: process.env.KEYDB_PASSWORD,
});

client.on('error', (err) => console.error('KeyDB error:', err));
client.connect().catch(console.error);

const server = http.createServer(async (req, res) => {
  if (req.url !== '/health') {
    res.writeHead(404);
    res.end();
    return;
  }

  try {
    const start = Date.now();
    await client.ping();
    const latencyMs = Date.now() - start;

    const info = await client.info('server');
    const versionMatch = info.match(/keydb_version:(.+)/);
    const version = versionMatch ? versionMatch[1].trim() : 'unknown';

    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({
      status: 'ok',
      latency_ms: latencyMs,
      keydb_version: version,
    }));
  } catch (err) {
    res.writeHead(503, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({
      status: 'error',
      message: err.message,
    }));
  }
});

server.listen(8080, () => console.log('Health server on :8080'));

Run it alongside KeyDB:

npm install redis
KEYDB_HOST=127.0.0.1 KEYDB_PORT=6379 node keydb-health.js

Or as a systemd service:

# /etc/systemd/system/keydb-health.service
[Unit]
Description=KeyDB health check proxy
After=keydb.service
Requires=keydb.service

[Service]
Type=simple
User=keydb-health
EnvironmentFile=/etc/keydb-health/env
ExecStart=/usr/bin/node /opt/keydb-health/keydb-health.js
Restart=always
RestartSec=5

[Install]
WantedBy=multi-user.target

sudo systemctl enable --now keydb-health
curl http://localhost:8080/health
# {"status":"ok","latency_ms":1,"keydb_version":"6.3.4"}

Expose port 8080 (or proxy it via nginx) so Vigilmon can reach it from outside the host.

Step 3: Set up HTTP monitoring in Vigilmon

  1. Log in to vigilmon.online and go to Monitors → New Monitor
  2. Choose HTTP / HTTPS as the monitor type
  3. Set the URL to your health endpoint: https://keydb.example.com/health
  4. Set the check interval to 1 minute
  5. Under Expected response, configure:
    • Status code: 200
    • Response body contains: "status":"ok"
  6. Save the monitor

Multi-region consensus for cache services

Vigilmon's multi-region probing is particularly useful for cache services. A cache miss caused by network issues between your application region and your KeyDB host looks identical to application-layer cache misses. By verifying connectivity from multiple geographic regions, Vigilmon can distinguish a genuine KeyDB outage (all regions fail) from a regional network blip (one region fails, others succeed).

Step 4: Set up TCP port monitoring

TCP monitoring directly probes KeyDB's port, independent of the health proxy. This catches port binding failures and firewall rule changes that the HTTP monitor might not see if the health proxy is on a different host:

  1. In Vigilmon, go to Monitors → New Monitor
  2. Choose TCP Port
  3. Enter your KeyDB host and port: keydb.example.com / 6379
  4. Save the monitor

For active-active KeyDB setups, add a TCP monitor for each node:

keydb-node-1.example.com:6379
keydb-node-2.example.com:6379

If one node's TCP monitor fires while the other stays green, you have a node-level failure rather than a network-level failure — a critical distinction for active-active debugging.

Step 5: Monitor replication health

For KeyDB replica setups (passive or active-active), extend your health proxy to check replication state:

// Extended health check with replication status
async function replicationHealth(client) {
  const info = await client.info('replication');
  const role = (info.match(/role:(.+)/) || [])[1]?.trim();
  const connectedSlaves = parseInt(
    (info.match(/connected_slaves:(\d+)/) || [])[1] || '0'
  );
  const masterLinkStatus = (info.match(/master_link_status:(.+)/) || [])[1]?.trim();

  if (role === 'master' && connectedSlaves === 0) {
    return { status: 'degraded', reason: 'no replicas connected' };
  }
  if (role === 'slave' && masterLinkStatus !== 'up') {
    return { status: 'degraded', reason: `master link: ${masterLinkStatus}` };
  }
  return { status: 'ok', role, connectedSlaves };
}

Expose this at /health/replication and add a second Vigilmon monitor with:

  • Expected status: 200
  • Alert on 503 (degraded replication)

Step 6: Set up a heartbeat for scheduled cache warming

If you run a periodic cache warming job (pre-populating KeyDB after restarts), monitor it with a heartbeat:

#!/bin/bash
# cache-warm.sh

redis-cli -h keydb.example.com -p 6379 FLUSHDB

# Load hot keys from your data source
while IFS= read -r key; do
  redis-cli -h keydb.example.com -p 6379 SET "$key" "$(fetch_value $key)" EX 3600
done < /var/cache/hot-keys.txt

# Report success
curl -fsS "https://vigilmon.online/api/v1/heartbeat/YOUR_HEARTBEAT_ID"

In Vigilmon, create a Heartbeat monitor with an interval matching your cache warming schedule. If the job fails or stalls, an alert fires before stale or empty caches impact your application.

Step 7: Configure alert channels

KeyDB outages cascade quickly — a cache miss storm can bring down a database. Configure alerts to fire immediately:

Email

  1. In Vigilmon, go to Alert Channels → Add Channel → Email
  2. Enter your on-call engineer's email
  3. Assign to all KeyDB monitors

Webhook (Slack or PagerDuty)

  1. Go to Alert Channels → Add Channel → Webhook
  2. Enter your Slack webhook or PagerDuty endpoint
  3. Assign to all monitors

Example Vigilmon webhook payload:

{
  "monitor_name": "KeyDB TCP :6379",
  "status": "down",
  "host": "keydb.example.com",
  "port": 6379,
  "started_at": "2024-01-15T10:23:00Z",
  "duration_seconds": 45
}

Use this to auto-trigger a KeyDB restart if the outage persists:

# Webhook handler
if [ "$STATUS" = "down" ] && [ "$DURATION_SECONDS" -gt 60 ]; then
  sudo systemctl restart keydb
fi

Step 8: Create a cache infrastructure status page

  1. In Vigilmon, go to Status Pages → New Status Page
  2. Name it "Cache Infrastructure"
  3. Add all KeyDB monitors (HTTP health, TCP nodes, replication, heartbeat)
  4. Publish and share with your backend team

Monitoring reference

| Monitor | Type | What it catches | |---------|------|-----------------| | https://keydb.example.com/health | HTTP | KeyDB crash, connection refused, app-layer failures | | keydb.example.com:6379 | TCP | Port binding failures, firewall changes | | keydb-node-2.example.com:6379 | TCP | Active-active node failures | | /health/replication | HTTP | Disconnected replicas, master link failures | | Cache warming CronJob | Heartbeat | Stalled or failed cache warming jobs |

Useful KeyDB debugging commands when alerts fire:

# Check KeyDB process
sudo systemctl status keydb
ps aux | grep keydb

# Ping and latency test
redis-cli -h keydb.example.com ping
redis-cli -h keydb.example.com --latency-history -i 5

# Memory usage
redis-cli -h keydb.example.com info memory | grep -E "used_memory_human|maxmemory_human"

# Replication state
redis-cli -h keydb.example.com info replication

# Connected clients
redis-cli -h keydb.example.com info clients

# Slow query log
redis-cli -h keydb.example.com slowlog get 10

# Active threads (KeyDB-specific)
redis-cli -h keydb.example.com info server | grep thread

What's next

  • SSL certificate monitoring — if KeyDB runs with TLS (tls-port), Vigilmon monitors certificate expiry and alerts before renewal is needed
  • Multi-node coverage — for active-active clusters, add a monitor per node and group them under a single status page to see at a glance which nodes are healthy
  • Database-level protection — pair KeyDB monitoring with your primary database monitoring so you can distinguish "cache is down" from "everything is down" during incidents

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