Your servers are running. Your code is flawless. Your CDN is configured perfectly.
But your website is completely unreachable.
The culprit? DNS failure — and you had no idea until customers started complaining.
DNS (Domain Name System) is the invisible foundation of the internet. It translates human-readable domain names like yoursite.com into IP addresses that computers use to connect. Without working DNS, nothing else matters. Your site simply doesn't exist.
Yet most monitoring setups completely ignore DNS. They check if the server responds — but by the time that check runs, DNS has already done its job. If DNS fails, the check never even reaches your server.
In this guide, we'll cover why DNS monitoring is critical, what can go wrong, and how to catch DNS issues before they take down your entire online presence.
Why DNS Is the Most Critical (and Ignored) Layer
Think of DNS as the phone book of the internet.
When a user types yoursite.com, their browser asks DNS servers: "What's the IP address for this domain?" Only after getting an answer can the browser connect to your server.
Here's why this matters:
DNS failure = total failure
If your web server goes down, users see an error page. Frustrating, but they know something's wrong.
If DNS fails? Users see "This site can't be reached" or "DNS_PROBE_FINISHED_NXDOMAIN." Many assume they have a connection problem. Or worse — they think your business shut down.
DNS issues are invisible to standard monitoring
Most uptime monitors work like this:
- Resolve the domain name to an IP address
- Connect to that IP address
- Check the response
If step 1 fails, many monitors simply report "connection failed" — giving you no insight that DNS was the actual problem.
DNS propagates slowly
When DNS breaks or when you make changes, it doesn't fail everywhere at once. Some users might reach your site fine while others can't connect at all. This makes DNS issues incredibly difficult to diagnose without proper monitoring.
Real-World DNS Disasters
DNS failures have taken down some of the biggest names on the internet:
The Dyn Attack (2016)
A massive DDoS attack against DNS provider Dyn took down Twitter, Netflix, Reddit, Spotify, and dozens of other major sites for hours. These companies' servers were fine — but nobody could reach them because DNS was unreachable.
Lesson: Your DNS provider is a single point of failure. If they go down, you go down.
Cloudflare Outage (2020)
A router misconfiguration at Cloudflare caused widespread DNS resolution failures. Millions of websites became unreachable for 27 minutes. For e-commerce sites, those 27 minutes cost real money.
Lesson: Even the most reliable providers have outages. You need to know immediately when it happens.
Microsoft Azure DNS (2021)
A DNS configuration error at Microsoft caused Azure services to become unreachable for customers worldwide. The issue cascaded through dependent services, affecting everything from Teams to Xbox Live.
Lesson: DNS failures cascade. A single misconfiguration can bring down entire ecosystems.
Facebook's 6-Hour Outage (2021)
A BGP routing change accidentally withdrew the routes to Facebook's DNS servers. The result? Facebook, Instagram, and WhatsApp were completely unreachable for over 6 hours — one of the longest outages in their history.
Lesson: DNS infrastructure is complex, and human error can cause catastrophic failures.
What Can Go Wrong With DNS
DNS seems simple, but there are many failure modes:
1. DNS provider outages
Your DNS provider (Cloudflare, Route 53, Google Cloud DNS, etc.) experiences downtime. If you rely on a single provider, you inherit their availability.
2. Expired domains
It sounds ridiculous, but major companies have let their domains expire. When a domain expires, DNS records become invalid, and your site vanishes from the internet.
3. Misconfigured records
A typo in a DNS record, an accidentally deleted A record, or a wrong IP address. These mistakes are easy to make and can take your site down instantly.
4. TTL (Time To Live) problems
TTL determines how long DNS resolvers cache your records. Set it too high, and DNS changes take forever to propagate. Set it too low, and you're dependent on your DNS provider being fast and available for every request.
5. DNSSEC failures
If you use DNSSEC for security, misconfigurations can cause validation failures — making your domain unreachable for security-conscious resolvers.
6. Propagation delays
After making DNS changes, it can take hours (or even days) for those changes to reach all DNS resolvers worldwide. During this time, some users can reach your site and others can't.
7. Nameserver delegation issues
If your domain registrar and DNS provider are different, nameserver delegation must be correctly configured. Mistakes here are common and devastating.
The Cascading Impact of DNS Failures
When DNS fails, everything fails:
| What Breaks | Why |
|---|---|
| Main website | Users can't resolve your domain |
| API endpoints | Third-party integrations fail |
| Email delivery | MX records become unreachable |
| CDN | Edge servers can't be located |
| Subdomains | app.yoursite.com, api.yoursite.com all fail |
| SSL certificate validation | Some validation methods require DNS |
| Webhooks | Services can't reach your callback URLs |
A DNS failure isn't just a website outage. It's a complete business outage.
Your customers can't reach you. Your partners' integrations break. Your emails bounce. Your entire digital presence disappears.
What DNS Monitoring Should Check
Effective DNS monitoring goes beyond "can I resolve this domain?" Here's what to monitor:
1. Resolution success
Can the domain be resolved at all? This is the most basic check, but it catches complete DNS failures.
2. Resolution time
How long does DNS resolution take? Slow DNS adds latency to every single request. If resolution time spikes, it's an early warning of problems.
3. Correct IP address
Does the domain resolve to the expected IP address? Catching when records return wrong IPs helps identify hijacking attempts or configuration errors.
4. All record types
Don't just check A records. Monitor:
- A/AAAA records — IPv4 and IPv6 addresses
- MX records — Email routing
- CNAME records — Aliases
- TXT records — SPF, DKIM, and verification records
- NS records — Nameserver delegation
5. Multiple DNS resolvers
Your DNS might work from one location but fail from another. Check from multiple global locations and different DNS resolvers (Google 8.8.8.8, Cloudflare 1.1.1.1, etc.).
6. Nameserver health
Monitor your authoritative nameservers directly. Are they responding? Are they returning consistent answers?
7. DNSSEC validation
If you use DNSSEC, verify that signatures are valid and chains are complete.
DNS Monitoring Best Practices
Use multiple DNS providers
Don't put all your eggs in one basket. Consider using two DNS providers (e.g., Cloudflare + Route 53) with automatic failover. This adds complexity but dramatically improves resilience.
Monitor from outside your infrastructure
If your DNS monitoring runs on the same infrastructure as your DNS, you'll miss failures that affect both. Use external monitoring that's completely independent.
Set appropriate alert thresholds
- Resolution failure: Alert immediately
- Resolution time > 100ms: Warning
- Resolution time > 500ms: Critical
- Wrong IP returned: Alert immediately
Monitor more than just your apex domain
Check all critical subdomains:
www.yoursite.comapi.yoursite.comapp.yoursite.commail.yoursite.com
Track DNS propagation after changes
When you make DNS changes, monitor propagation across global resolvers. Don't assume the change worked until you verify it everywhere.
Keep TTLs reasonable
- Normal operation: 300-3600 seconds (5 minutes to 1 hour)
- Before planned changes: Lower to 60-300 seconds
- During incidents: Be aware that high TTLs mean cached bad records persist longer
Document your DNS configuration
Know exactly what records you have, why they exist, and what depends on them. When something breaks at 3 AM, you'll be grateful for documentation.
How DNS Monitoring Fits Into Your Stack
DNS monitoring complements your existing uptime monitoring:
| Monitoring Type | What It Catches |
|---|---|
| Uptime monitoring | Server down, application errors, network issues |
| SSL monitoring | Certificate expiration, chain problems |
| Response time monitoring | Performance degradation, slow backends |
| DNS monitoring | Resolution failures, wrong records, propagation issues |
Together, these give you complete visibility into your availability. A gap in any layer leaves you blind to specific failure modes.
How Webalert Helps With DNS Reliability
Every Webalert monitor automatically tracks DNS as part of the check:
DNS resolution timing
See exactly how long DNS resolution takes for each check. Catch slowdowns before they impact users.
Resolution from multiple regions
Checks from global locations ensure you catch region-specific DNS issues — not just problems visible from one location.
Complete connection breakdown
When something fails, you'll see exactly where: DNS resolution, TCP connection, TLS handshake, or server response.
Instant alerts
Get notified via email or SMS the moment DNS issues are detected. Don't wait for customer complaints to learn about problems.
Historical tracking
Review DNS performance over time. Spot trends and catch degradation before it becomes critical.
DNS Health Check Questions
Ask yourself:
- Do you know who your DNS provider is and their uptime SLA?
- When was the last time you verified your DNS records are correct?
- Do you have monitoring that would catch a DNS failure specifically?
- What's your plan if your DNS provider has an outage?
- Do you monitor DNS from multiple geographic locations?
- When did your domain registration last renew? When does it expire next?
If you hesitated on any of these, your DNS is a potential blind spot.
Final Thoughts
DNS is the foundation everything else depends on.
Your servers can have perfect uptime. Your code can be flawless. Your infrastructure can be world-class. But if DNS fails, none of it matters. Your site is gone.
The irony? DNS failures are among the easiest to prevent with proper monitoring. You know exactly what to check. The infrastructure is external and stable. The failure modes are well-understood.
Yet most teams don't monitor DNS at all. They wait for the support tickets to roll in, then scramble to figure out why "the site is down" when their server dashboards show everything green.
Don't be that team.
Add DNS to your monitoring stack. Check resolution from multiple locations. Alert on failures immediately. Know your DNS provider's status before your customers tell you.
The foundation of your website deserves more than hope.
Ready to monitor the foundation?
Start monitoring your DNS free with Webalert →
Complete visibility. Instant alerts. No more DNS surprises.