Mastering Domain Control with Azure DNS
The internet operates on a complex infrastructure where the domain name system (DNS) plays a pivotal role. If you’ve ever wondered how domain names translate to IP addresses or how cloud providers like Azure manage this crucial piece, this article dives deep into hosting your DNS zones and handling DNS records with Azure’s platform. DNS management, often underestimated, is the backbone of seamless connectivity and robust network performance.
When you host your DNS zone on Azure, you gain the ability to oversee and configure your DNS records meticulously. A DNS zone is essentially a container for DNS records that share a common domain namespace. Azure allows the creation and management of both private and public DNS zones, giving you comprehensive control over your network’s address resolution — whether it’s exposed to the public internet or confined within private virtual networks.
The Fundamentals of DNS Zones and Records
At its core, a DNS zone acts like a directory where different types of DNS records are stored. These records map domain names to IP addresses or other domains, guiding user requests to the right destinations. Azure DNS facilitates various record types, but a foundational understanding of alias recordsets is paramount.
Azure supports alias recordsets that streamline the way you link domain names to IP addresses or other domain names:
- The A record links a host to an IPv4 address, the classic 32-bit format used by the vast majority of the internet.
- The AAAA record corresponds to IPv6 addresses, which are 128-bit and designed to alleviate IPv4 exhaustion.
- The CNAME record allows you to alias one domain name to another, effectively redirecting traffic without changing the destination IP directly.
However, there’s a cap: you can create up to 20 alias record sets per resource, a limitation that enforces prudent DNS architecture and avoids excessive record proliferation.
Anycast Networking for Optimal Routing
Azure DNS leverages Anycast networking technology, an ingenious system where multiple geographically dispersed servers share the same IP address. This enables DNS queries to be routed to the closest or best-performing name server based on network topology and latency, rather than a single fixed server.
This proximity-based routing minimizes query response times and enhances fault tolerance. If one server faces downtime, Anycast reroutes requests to the next nearest server, keeping DNS resolution resilient and uninterrupted.
Monitoring Your DNS Zones With Azure Monitor
Efficient DNS management isn’t only about setting up records; it also involves continuous monitoring. Azure Monitor integrates seamlessly with DNS zones, providing valuable metrics to track the health and performance of your DNS setup.
Some key metrics include:
- QueryVolume: This metric records the total number of DNS queries your zone receives, offering insights into traffic patterns and potential spikes.
- RecordSetCount: This counts the number of record sets present in your DNS zone, helping you manage the scale and complexity of your DNS infrastructure.
- RecordSetCapacityUtilization: This percentage indicates how much of your allocated record capacity is being utilized, alerting you to potential resource constraints or inefficiencies.
Leveraging these metrics allows network administrators to make informed decisions about scaling, optimizing, or troubleshooting their DNS infrastructure proactively.
Private and Public DNS Zones: Defining the Scope
Public DNS zones are accessible globally, serving public-facing domains such as your company website or application endpoint. Private DNS zones, on the other hand, operate within a closed virtual network (VNet) environment. This allows enterprises to manage internal domain name resolution without exposing sensitive records to the outside world.
Using Azure Private DNS, organizations can maintain custom domain names exclusively within their private networks. This segregation of namespace is critical for internal services, microservices architectures, or hybrid cloud environments where security and privacy are paramount.
Navigating Private DNS in Azure: Internal Name Resolution and Advanced Configurations
In a cloud-native world where applications are fragmented across multiple services, networks, and environments, internal communication becomes just as critical as public exposure. Enter Azure Private DNS — a feature tailored to modern architectures that need secure, efficient name resolution strictly within private networks. If you’re tired of jumping through hoops to resolve hostnames inside your VNets, this solution might just be your new best friend.
What Is Private DNS, and Why Does It Matter?
At its core, private DNS enables name resolution within virtual networks without sending DNS queries over the public internet. This isn’t just about convenience — it’s a major boost in security and efficiency.
Let’s say your application is split across several services inside Azure — a database, a few APIs, and a couple of microservices. You want those services to communicate using easy-to-read domain names, not cryptic IP addresses. Private DNS gives you this capability without needing to expose anything to the outside world. This is mission-critical for organizations that prioritize internal security, regulatory compliance, or just want to avoid unnecessary public exposure.
With Azure Private DNS, you gain fine-grained control over how internal domains resolve and what networks can use those records.
Custom Domain Names in Your Private VNet
Traditionally, without private DNS, you’d have to manually edit host files or use custom DNS servers. That’s not only painful to scale, but it’s also prone to misconfiguration. Azure Private DNS removes that friction by allowing you to define custom domain names and resolve them automatically within your VNet.
Instead of dealing with domains generated by Azure, you can now use internal-friendly domains which are far easier to manage, recognize, and audit. You define the records once, and they propagate across linked networks — no hacks, no third-party DNS servers, and no ugly workarounds.
Linking Virtual Networks to a Private Zone
One of the most useful — and sometimes misunderstood — aspects of Azure Private DNS is how it links to virtual networks.
Each private DNS zone can be connected to multiple virtual networks, enabling shared domain resolution across them. For example, if you have a production VNet, a staging VNet, and a dev VNet, all of them can resolve the same internal domains if they’re linked to the same zone.
However, there’s a catch: each virtual network can only be linked to one private zone for any given namespace. This means you can’t have two different private zones connected to the same VNet without creating a conflict. Planning your zone structure carefully upfront avoids headaches down the line.
This linking structure is what powers cross-VNet name resolution — a game-changer in large, distributed environments. It lets teams work in parallel VNets without reinventing DNS wheels for each environment.
Split-Horizon DNS: Same Name, Different Responses
One of the more sophisticated features of Azure DNS is split-horizon DNS (also known as “split-brain DNS”). This allows you to have both a private and public DNS zone with the same name, but different records.
Split-horizon DNS makes this possible. The Azure DNS service detects whether the client making the request is inside the virtual network or coming from the internet and serves the appropriate record. This technique is particularly powerful in hybrid networks or when building secure access gateways. You can ensure internal clients get optimal, private routing while external users access the public endpoints.
Supported DNS Record Types
Azure Private DNS supports every major DNS record type you might need, including some often overlooked ones:
- A and AAAA: IPv4 and IPv6 address mappings.
- CNAME: Canonical name (alias) records for redirecting names.
- MX: Mail exchange records for email routing.
- PTR: Pointer records for reverse lookups, used in validating the sender of an email or for compliance.
- SOA: Start of authority, which defines the zone’s settings and default parameters.
- SRV: Service locator records, crucial in systems like Microsoft Active Directory or VoIP setups.
- TXT: Text records, often used for security purposes like SPF, DKIM, and domain verification.
The breadth of supported record types makes Azure Private DNS not just a basic resolver but a comprehensive internal DNS platform capable of supporting enterprise-level complexity.
Alias Records for Traffic Manager and CDN Endpoints
Azure’s support for alias records extends to private zones too. These let you point your naked domain (apex) to Azure resources such as Traffic Manager profiles or CDN endpoints without needing to resolve to an IP address first.
This is especially helpful when you’re building dynamic or distributed applications that use Azure’s load balancing or content delivery services. Instead of hardcoding IPs or manually updating records every time your backend changes, alias records dynamically resolve the current target. It brings both resilience and automation into your internal DNS architecture — a major win for scaling apps without DNS becoming a bottleneck.
Reverse DNS for Private IP Spaces
In many security-sensitive environments, reverse DNS (rDNS) is just as important as forward DNS. It allows you to resolve IP addresses back to domain names, which is useful for:
- Security audits
- Email validation
- Log readability
- Access control
Azure Private DNS supports reverse DNS lookups inside the linked virtual network, which is a massive improvement over manual PTR record management. This functionality allows seamless integration with logging systems, authentication mechanisms, and observability tools that rely on reverse lookups to add context to IP addresses.
Operational Simplicity with Azure Integration
One of the underrated benefits of Private DNS is how well it integrates with the rest of Azure’s services. You don’t need to deploy custom DNS servers or build fragile chains of infrastructure just to handle name resolution.
For example, when deploying a Kubernetes cluster inside Azure Kubernetes Service (AKS), you can hook it up to a private DNS zone to let pods resolve internal services with familiar domain names. Or, when connecting on-prem networks through ExpressRoute or VPN Gateway, you can link those networks to the same zone for seamless hybrid name resolution.
The native integration minimizes complexity, reduces points of failure, and helps teams focus on delivering services — not babysitting DNS infrastructure.
Azure Private DNS isn’t just an accessory — it’s a foundational building block for private, secure, scalable networks in the cloud. With features like zone linking, split-horizon configurations, alias records, and reverse DNS support, it gives organizations the tooling they need to manage internal domains like a pro.
If you’re working in multi-VNet architectures, securing internal apps, or building hybrid solutions, Private DNS can eliminate a ton of overhead and boost operational clarity. Its elegant integration with Azure’s ecosystem makes it both powerful and painless to maintain — which is exactly what modern infrastructure should aim for.
Locking Down Azure DNS: Security, Role Control, and Firewalls
DNS is one of the most heavily targeted and overlooked parts of any system. It’s a soft underbelly attackers often exploit for reconnaissance, redirection, and data exfiltration. If you’re managing DNS in Azure, ignoring security is like leaving your front door wide open in a sketchy neighborhood and expecting nothing to happen. That’s why Azure DNS comes loaded with features that help you harden your zone configurations, restrict access, and block malicious queries — assuming you actually use them.
The Problem with Default Permissions
By default, Azure’s role-based access control (RBAC) gives users way more power than they often need. If someone has Contributor access to a DNS zone resource group, they can not only update records but also delete entire DNS zones. That’s not just overkill — it’s dangerous.
Zone deletions can cripple entire applications. Imagine accidentally wiping out the DNS records for your production website. No DNS, no traffic. And unless you’ve got backups, you’re manually piecing things back together in a panic.
Preventing Zone Deletion with Resource Locks
Azure gives you a blunt but effective tool to stop accidental or unauthorized deletions: resource locks. Specifically, the CanNotDelete lock.
This lock attaches to your DNS zone and ensures no one can delete it, even if they have permission to delete other resources. Any attempt to remove the zone throws an error — until someone explicitly removes the lock first. It’s not glamorous, but it works. And it works better than relying on everyone to follow best practices all the time.
You can apply the CanNotDelete lock via the Azure Portal, PowerShell, Azure CLI, or an ARM template. Once applied, it adds an extra layer of intention — someone has to knowingly remove the lock before doing something destructive.
It doesn’t stop modifications (that’s a separate lock type, ReadOnly, which is usually too restrictive for DNS), but it gives you just enough protection to avoid nuking your own zone by mistake.
Custom Roles: Granular Access Control That Actually Works
RBAC in Azure is powerful, but only if you use it correctly. Most teams lazily assign built-in roles like Contributor or Owner, which are basically handing people full control. That might be fine in dev environments, but in production, it’s reckless.
Creating a custom role specifically for DNS management lets you strip out dangerous permissions — like zone deletion — while still allowing necessary actions like record creation or updates.
You define a JSON role definition with only the required actions you actually need. For example, allow read, write, list, but exclude delete. Assign this custom role only to users or services that actually manage DNS — not everyone on the team.
This method is more work up front, but it avoids giving away keys to the kingdom for convenience. It also plays nice with auditing, since you know exactly who has access to what.
DNS Firewall: Your First Line of Defense Against Malicious Queries
If you think DNS isn’t a major attack vector, think again. DNS tunneling, cache poisoning, DDoS attacks, and exfiltration over DNS are all common exploits. Unfortunately, traditional firewalls and endpoint protection rarely catch these because DNS looks benign — until it’s not.
Azure provides a DNS firewall solution that lets you filter DNS queries before they ever reach your DNS zones. It acts as a gatekeeper, inspecting requests and enforcing rules to allow or block traffic based on source IPs, domain names, query types, or even response codes.
This is particularly important if you’re:
- Running internal-only applications
- Worried about data leaking through DNS channels
- Facing DNS floods or suspicious traffic patterns
You can configure rules to allowlist trusted domains, deny wildcard patterns, or even redirect blocked queries to a sinkhole for logging. This adds a layer of visibility and control that just doesn’t exist with unmanaged public resolvers.
It’s also scalable. You can apply policies across multiple zones or resource groups without micromanaging settings individually. Think of it like DNS ACLs with brains.
DNS Logging and Threat Detection
You can’t protect what you don’t see. Azure Monitor and DNS Analytics via Log Analytics let you capture detailed DNS query logs, which are crucial for tracking what’s really happening under the hood.
These logs help you spot:
- Query spikes that might indicate a DNS flood
- Unusual patterns, like clients querying weird or unknown domains
- Lookups that hint at DNS tunneling or malware trying to reach command-and-control servers
You can set up alerts for anomalies — like more than 1,000 TXT record queries in a minute (a red flag for DNS exfiltration) — or use Kusto queries to drill down into logs for incident response.
DNS logs might seem boring, but they’re forensic gold when something goes wrong.
Securing Private DNS Zones
Private DNS zones need just as much — if not more — protection than public ones. Just because they’re hidden from the internet doesn’t mean they’re safe. Internal threats, misconfigurations, and compromised VMs can wreak havoc without proper controls.
First, apply the same deletion locks and custom roles as you would with public zones. Then go further:
- Use NSG rules to limit which VMs can resolve private DNS.
- Audit zone links — don’t just connect every VNet “just in case.”
- Avoid wildcard records unless absolutely necessary — they make lateral movement easier if compromised.
You can also integrate private DNS with Azure Policy, enforcing rules like “Only approved VNets can link to a private zone” or “Zones must be locked.”
Internal security is often overlooked, but once a threat actor is inside, they’re counting on you to be lazy. DNS misconfigurations often provide the path forward.
Conditional Forwarding and DNS Proxying
For more advanced setups, Azure allows conditional forwarding using custom DNS servers. This is useful when you want DNS queries for certain domains to go to specific name servers — like on-premises Active Directory DNS.
Instead of forwarding everything to Azure DNS, you can forward only certain domains while resolving others in Azure. It’s DNS routing logic without needing BGP or any heavy lifting.
Some teams deploy DNS proxy VMs (using tools like BIND, Unbound, or dnsmasq) in tightly controlled subnets to handle forwarders with extra logic or logging.
If you’re in a hybrid cloud setup, this allows tight control over DNS flows, minimizes query leakage to public resolvers, and centralizes logs for auditing.
Don’t Forget About DNS TTL and Caching Behavior
Security isn’t just about firewalls and access controls. It’s also about how fast DNS changes propagate and how cacheable your records are.
If your TTLs (Time To Live) are too high, a bad record can linger in downstream caches for hours or even days. If they’re too low, you’ll hammer your DNS servers and potentially expose yourself to timing attacks or query floods.
Find a balance. For static records like MX or SOA, longer TTLs (3600–86400 seconds) are fine. For records you might change during failover or disaster recovery, keep them shorter (60–300 seconds). This way, you don’t have to wait forever for stale entries to expire.
Also, pay attention to negative caching — failed lookups can be cached too, which can make debugging a nightmare if not understood.
Understanding Azure DNS Pricing: Billing, Queries, and Strategic Cost Control
For a service as invisible-yet-crucial as DNS, cost often gets ignored — until your monthly bill shows up with a surprise. Unlike compute or storage, DNS charges can seem minimal upfront but become unexpectedly bloated once you scale or misconfigure something. So if you’re running infrastructure on Azure and using its DNS services, you should understand not only how pricing works but how to strategically optimize it.
This isn’t just about cutting costs. It’s about ensuring you don’t bleed money through background processes, recursive queries, or careless record sprawl.
How Azure DNS Pricing Actually Works
Azure DNS doesn’t charge by uptime or by how many people look at your zone file. Instead, it bills you based on two main factors:
- Number of DNS zones hosted
- Number of DNS queries received
It’s a classic pay-for-what-you-use model — which is great for flexibility, but also means any mistake can get expensive quickly.
Hosted Zones: Flat Monthly Cost Per Zone
A DNS zone is the container for your domain and all its records. Each one incurs a flat monthly fee.
- You’re billed per public DNS zone and per private DNS zone, separately.
- There’s no discount for empty zones. Even if your zone has only one record and barely any traffic, you still get billed the same.
This can creep up on you if you create zones automatically through scripts or infrastructure-as-code pipelines and forget to clean them up. Especially during dev and testing cycles, it’s easy to end up with dozens of unused zones just sitting there, burning dollars.
DNS Queries: Volume-Based, Not Bandwidth-Based
Every time someone queries your domain — whether for an A record, MX record, or even an NXDOMAIN response (record doesn’t exist) — you get charged. This includes:
- Public users resolving your website
- Internal services looking up private DNS names
- Misconfigured bots hammering non-existent subdomains
- Monitoring systems checking endpoints every few seconds
Query charges are per million requests, and the rates differ slightly between public and private zones. Azure doesn’t care if the query succeeded or failed — a query is a query.
There’s no cap or rate throttling. So if your domain suddenly becomes a target of a DNS-based denial-of-service attempt, your bill will reflect that unless you have mitigation measures in place.
Digging Into DNS Metrics: QueryVolume and RecordSetCount
To help you make sense of your usage and costs, Azure DNS exposes several built-in metrics:
QueryVolume
This tells you how many DNS queries your zones are processing. It’s the most direct contributor to your monthly cost. You should monitor this for:
- Unexpected spikes (could indicate abuse or bot traffic)
- Chronic high volumes from internal systems
- Recurring background traffic that serves no real purpose
Sometimes it’s just your CI/CD system going wild. Other times it’s a misconfigured container pinging a nonexistent domain 100 times a second. Either way, this metric keeps you honest.
RecordSetCount
This shows how many DNS records you have in each zone. While this doesn’t directly affect pricing, it does impact manageability and potentially latency in DNS responses. Overloading your zones with thousands of unused or test records can slow things down and confuse teams trying to troubleshoot.
It’s especially common in dynamically managed zones where services register themselves and forget to unregister on shutdown. If your automation doesn’t clean up old entries, your zone turns into digital clutter.
RecordSetCapacityUtilization
Each zone has a soft limit on how many records it can contain — and this metric shows what percentage of that limit you’ve used. This is important in large-scale environments because:
- Hitting 100% blocks new record creation.
- High utilization can introduce management delays or sync issues.
- You may need to request a limit increase or break your zone into multiple sub-zones.
This isn’t about cost, per se — it’s about avoiding operational bottlenecks. But ignoring it can still lead to service outages that cost you in downtime, missed SLAs, or frantic midnight Slack alerts.
Cost Optimization Tips: Stop Burning Cash with Every Query
If you’re not watching DNS usage, it’s easy to pay way more than you should. Here’s how to avoid that.
1. Avoid Noisy Query Patterns
Monitoring systems, load balancers, and service discovery tools can hit DNS records constantly. If they’re set with super-low TTLs, you’re paying for every lookup.
Fix: Set higher TTLs (Time To Live) where appropriate. For stable records (like your public site’s A record or mail server), a TTL of 3600 seconds or more reduces repeated lookups.
This reduces not only query volume but also latency for users, since they can cache the results longer.
2. Audit Unused Zones Regularly
It’s not uncommon to have 20–30 zones created over time for dev/test, client demos, or sandbox projects that never get deleted.
Fix: Set up a regular audit. If a zone has no recent query activity and hasn’t been updated in weeks, mark it for cleanup. Use tags to label environments (prod, test, sandbox) and automate retirement policies based on those.
3. Use Alias Records Wisely
Alias records are powerful — they allow root domains to point directly to Azure resources like Traffic Manager or CDN endpoints. But they can also introduce dynamic lookups that bypass caching, especially if the underlying target IPs change frequently.
Fix: Where possible, avoid alias records in high-query, high-availability zones unless you really need them. Use CNAMEs or static A records if your infrastructure is relatively stable.
4. Don’t Over-Split Zones Without a Plan
Every new zone is a flat-rate cost. Breaking every service into its own subdomain and zone might sound like good separation of concerns — until you’re paying for dozens of low-traffic zones with no benefit.
Fix: Consolidate zones where it makes sense. You can still use subdomains under a single zone to keep costs low and management centralized.
5. Watch for Recursive Query Chains
Some misconfigurations lead to recursive DNS lookups that spiral into thousands of requests. This happens when a record points to a CNAME, which points to another CNAME, which eventually resolves… but the TTLs are low, and each service calls it repeatedly.
Fix: Flatten your records where possible. Reduce reliance on chained CNAMEs unless the service needs that flexibility.
Real-World Scenarios: Where Things Go Sideways
Scenario 1: A CDN Misconfiguration
A company configured an alias record at the root domain pointing to a CDN endpoint. But every user hit the page, and the TTL was set to 30 seconds. Result: tens of millions of queries per day. The CDN was fine, but the DNS bill tripled unexpectedly.
Scenario 2: Zombie Containers
A containerized service was configured to do health checks by repeatedly resolving an internal hostname. When thousands of these containers launched across a fleet, they created massive internal query storms — all billed under private DNS. No alerts were in place. The dev team noticed only after the Azure invoice arrived.
Scenario 3: Forgotten Test Zones
A developer created 15 test zones for a PoC, forgot about them, and left the company. The org paid for those zones for eight straight months before someone realized they weren’t used.
Azure DNS isn’t expensive — until you make it expensive. If you’re thoughtful about your configuration, you’ll spend pennies on a service that silently holds your infrastructure together. But if you ignore it, your DNS setup can become a quiet, invisible sinkhole for budget and reliability.
Monitor the metrics. Tag and audit your zones. Reduce query volume where it adds no value. And don’t assume “set it and forget it” applies here. DNS isn’t flashy — but in the cloud, it’s foundational. Treat it with the respect (and optimization) it deserves.
Conclusion
Azure DNS is far more than just a background utility — it’s a critical foundation for modern cloud infrastructure. Across these four deep dives, we’ve broken down how to effectively host and manage DNS zones, optimize for both public and private environments, implement airtight security, and avoid hidden costs that quietly drain budgets. From alias records and Anycast routing to granular RBAC controls and DNS firewall protection, Azure offers powerful tools — but only if you’re intentional about how you use them. Missteps like excessive zone sprawl, unchecked query traffic, and lax permissions can spiral into outages or inflated bills. DNS may be invisible when it’s working, but it’s the first thing to break everything when it doesn’t. The key takeaway? Treat DNS with the same care you give your computer or networking layers. Audit it, secure it, and streamline it. Because in the cloud, smart DNS management isn’t optional — it’s survival.
