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This guide shows how to design the endpoints, publish records, configure health checks and fallback behavior, choose a TTL, remove a failed server, and test failover without promising instant recovery. The examples apply to authoritative DNS platforms generally, with specific differences called out for Route 53, Cloudflare Load Balancing, and Azure Traffic Manager.
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What DNS round robin actually does
For one service name, such as www.example.com, you publish several address records. A resolver may return all of them, often in an order that changes between queries. Clients then try one address, or use their own connection-selection logic. The result is distribution of connection attempts rather than a measured distribution of workload.
www.example.com. 300 IN A 203.0.113.10
www.example.com. 300 IN A 203.0.113.11
www.example.com. 300 IN A 203.0.113.12IPv6 uses the same pattern with AAAA records. Cloudflare’s documented basic example is to create multiple A or AAAA records for the same hostname to randomly distribute traffic across servers.
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Why this is not automatic failover
Authoritative DNS does not normally open a TCP connection, request your application, or understand whether a database dependency is broken. If one address is down, it can continue to be published until an operator changes the zone. Some clients retry another address; others show an error after the first failed attempt. Long-lived connections remain on their original endpoint.
Round robin also does not account for current CPU use, connection duration, bandwidth, session state, or unequal server capacity. It is therefore suitable only when each endpoint can independently serve the same requests and occasional selection of an unavailable address is acceptable, or when a separate health-aware system controls which records are returned.
Plan the high-availability design first
Use independent failure domains
Choose at least two application endpoints. Place them in separate availability zones, regions, facilities, or network paths so that one infrastructure failure does not remove every endpoint. Give all endpoints the same public service hostname; do not make users choose a server-specific name.
- Each endpoint must serve the same application behavior and compatible API version.
- Each endpoint must present a certificate valid for the shared hostname, including any required subject-alternative names.
- Deploy the same authentication, authorization, and security policy on every endpoint.
- Replicate or externalize state that a request may need. DNS cannot synchronize sessions, uploads, queues, or databases.
- Document which endpoint is primary, which is secondary, and what happens if both are unhealthy.
Choose the health signal
Create a small health path such as GET /health. A useful check should confirm the dependencies required to serve real traffic, not merely that a web process can return a static 200 response. Decide whether the endpoint should be considered unhealthy when its database, cache, queue, identity service, or storage dependency is unavailable.
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Keep the health response quick and deterministic. Do not expose secrets or detailed internal diagnostics in a public response. If a dependency is optional, do not make it a reason to remove an otherwise usable endpoint. Record the exact protocol, port, path, expected status, timeout, check interval, and consecutive-failure and recovery thresholds.
Publish basic DNS round robin
- Inventory the authoritative zone. Confirm which DNS service is authoritative for the domain and identify the exact hostname users will call, such as
app.example.com. Make sure no conflicting CNAME, wildcard, proxied, or delegated record already controls that name. - Verify every endpoint directly. From a test network, connect to each address while sending the shared Host header and using the shared TLS name. Confirm the expected status code, redirects, authentication behavior, and application data.
- Create one record per address. Add an A record for each IPv4 address, or an AAAA record for each IPv6 address. Use the same name and TTL. If clients need both address families, publish both families deliberately and test how your clients select between them.
- Keep record settings consistent. Do not accidentally put one address behind a proxy and leave another as a direct DNS answer unless you understand the provider’s behavior. Proxied and unproxied records can follow different paths, and mixing them may produce unexpected results.
- Wait for authoritative publication. Query the authoritative nameservers and verify that all intended addresses are present. Then query at least two public recursive resolvers. A resolver may reorder or cache the answer, so a single query does not prove that every user sees the same order.
- Observe before declaring success. Check access logs, TLS handshakes, error rates, and latency on every endpoint. Confirm that traffic is reaching the intended servers and that no endpoint is serving a stale application build.
At this stage you have distribution, not health-aware availability. If a server fails, the address remains in DNS until its record is removed and caches expire.
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For high availability, use a DNS service or managed load-balancing feature that probes endpoints and suppresses unhealthy answers. The exact controls differ, but the design has the same elements: monitored resources, a routing policy, failure thresholds, and a defined response when all primary resources fail.
Route 53 health checks and routing
Route 53 can check resource health and answer DNS queries using only healthy resources. A simple health-checked configuration is appropriate when several equivalent web resources should receive traffic. More complex configurations can combine health checks with policies such as weighted, latency-based, geographic, or priority routing.
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- Create a health check for each endpoint, selecting the correct protocol, port, path, interval, timeout, and success criteria.
- Associate each DNS resource record with its corresponding health check. Verify that the check is evaluating the public path clients use, not an internal address that bypasses a failing component.
- Select the routing policy. Use simple or weighted behavior for equivalent endpoints; use priority or failover behavior when one endpoint should be preferred and another should be standby.
- Define the all-unhealthy result. Decide whether to return a designated secondary resource, a maintenance endpoint, or the last known set, and document the consequence for users.
- Query the authoritative response while deliberately failing one endpoint. Confirm that the failed address disappears according to the configured thresholds and that healthy addresses remain.
Cloudflare Load Balancing pools and monitors
Cloudflare separates basic DNS round robin from its Load Balancing feature. Load Balancing uses pools, monitors, health checks, and (where configured) a fallback pool. A pool groups origins that can serve the same traffic. The monitor can test responsiveness, timeout behavior, an expected HTTP status, and response content.
- Create an origin for each independent application endpoint and group equivalent origins in a primary pool.
- Create a monitor for the real health path. Set protocol, port, request method, interval, timeout, expected status, and any required response-content match.
- Attach the monitor to the pool and select the routing method offered for your plan, such as random, weighted, latency, geographic, or priority behavior.
- Configure a fallback pool if available. It is the last-resort destination when the primary pool has no healthy origin; choose a deliberately limited maintenance or recovery service rather than an untested endpoint.
- Check whether each DNS record is proxied or unproxied and keep the arrangement intentional. A proxied hostname and a direct DNS answer do not have identical failure and visibility characteristics.
Azure Traffic Manager probes and DNS routing
Azure Traffic Manager provides DNS routing with health probes. Its policies can direct users by priority, weighted distribution, performance, geographic location, or another supported method. The service returns DNS answers based on endpoint health, while the user’s resolver and client still cache and use those answers.
- Add each public application endpoint to the Traffic Manager profile.
- Configure the probe protocol, port, path, interval, timeout, and tolerated failures. The probe path should represent the minimum capability required for useful traffic.
- Choose a routing method that matches the objective: priority for active/standby, weighted for proportional distribution, performance for latency-oriented selection, or geographic rules for location-specific destinations.
- Set the DNS TTL on the profile and record. Azure documents 300 seconds in one high-availability example and recommends less than 60 seconds as an optimization for faster Traffic Manager updates; these are provider recommendations, not universal guarantees.
- Test both endpoint removal and restoration. Confirm the profile’s health state, the authoritative answer, and what a recursive resolver returns after its cached TTL expires.
Set a TTL that matches the recovery objective
TTL is the maximum caching period a resolver should use for an answer. A shorter TTL lets recursive resolvers request a new answer sooner after a record or health decision changes, but it increases DNS query volume and does not control every client. Some software caches beyond the nominal TTL, and an already-open connection is unaffected.
| Operational goal | TTL approach | Trade-off |
|---|---|---|
| Routine service with infrequent changes | Several minutes or more, subject to provider guidance | Fewer DNS queries, slower visibility of changes |
| Planned maintenance | Lower the TTL well before the change, then restore it afterward | Requires advance planning; old caches may still exist |
| Fast health-based failover | Use a short value supported by the provider; Azure guidance cites under 60 seconds as an optimization | More resolver traffic and still no instant, universal propagation |
| Documented Azure high-availability pattern | 300 seconds in Microsoft’s example | A provider example, not a guarantee for every topology |
Do not promise a five-minute or one-minute outage budget solely from the TTL. The observed delay also includes probe interval, failure thresholds, provider processing, recursive caching, client caching, and connection retry behavior. Measure the complete path in your own environment.
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How to remove a failed server safely
When using plain records
- Confirm the failure from more than one network and distinguish an application failure from a local monitoring problem.
- Delete the failed A or AAAA record, or set it inactive using your DNS provider’s change mechanism.
- Query the authoritative nameservers to verify the new set of records.
- Leave the record removed until the endpoint passes application and TLS checks again. Re-adding it before recovery can send users back to a broken server.
- After the incident, restore the intended record set and TTL only after verifying that caches and monitoring show normal behavior.
When using health-aware routing
Prefer changing the endpoint’s service state or fixing the health check rather than manually editing every DNS record. The provider should stop returning the resource after the configured consecutive-failure threshold. If the endpoint is undergoing planned maintenance, mark it disabled or drain it first so that new DNS answers avoid it while existing connections finish.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Failure-testing runbook
Run these tests before production and after material changes to probes, routing, certificates, or application dependencies.
- Baseline. Record the normal health state, authoritative answers, recursive answers, request distribution, and application error rate.
- Single-endpoint outage. Stop one web process or block its health path without changing the others. Confirm that the monitor detects the failure after the expected interval and threshold.
- Client behavior. Resolve the hostname through multiple recursive resolvers and test new connections from more than one network. Record how long cached answers continue to include the failed address.
- Dependency outage. Make a required database or identity dependency unavailable while leaving the web process running. Verify that the health path changes state; a static 200 response would conceal this failure.
- Probe failure modes. Test timeout, connection refusal, invalid certificate, unexpected status, and incorrect response content. Ensure each is classified as intended.
- All-primary failure. Fail every primary endpoint and verify the documented fallback pool, secondary region, or maintenance response. Confirm that the response is preferable to sending users to dead addresses.
- Recovery and failback. Restore one endpoint, wait for the recovery threshold, and verify that it re-enters routing only after it is genuinely ready. Repeat with the preferred endpoint if you use priority routing.
- Record evidence. Capture probe timestamps, authoritative DNS responses, recursive resolver results, client errors, and recovery times. Use these observations to set a realistic recovery objective.
Troubleshooting common symptoms
Users still reach the failed address
The answer may be cached until its TTL expires, or the client may have cached it independently. Check the timestamp and TTL returned by the recursive resolver, then test the authoritative nameserver to separate provider state from cache state. Existing keep-alive or WebSocket connections also remain on the old endpoint.
One server receives nearly all traffic
DNS round robin is not a packet scheduler. Resolver reuse, client connection pooling, unequal caching, and different network populations can make the distribution uneven. If proportional traffic matters, use weighted routing or an application-layer load balancer and measure at the origin rather than inferring distribution from DNS answers.
The monitor says healthy but users see errors
Your health path may check only the web process. Extend it to the dependencies required for real requests, or create separate readiness and liveness checks. Also verify the probe’s Host header, TLS name, redirect handling, authentication requirements, and expected status/content.
Failover happens too quickly or too slowly
Review probe interval, timeout, consecutive-failure threshold, recovery threshold, provider processing time, TTL, and client retry behavior as one chain. Lowering only the TTL cannot compensate for a long probe interval, and an aggressive threshold can remove a healthy endpoint during a transient network event.
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IPv4 and IPv6 behave differently
Check A and AAAA records separately. Some clients prefer IPv6 and may never use the IPv4 pool; others race both families. Give both families equivalent health coverage or remove an address family that cannot provide the same application and TLS behavior.
When DNS round robin is the wrong tool
Use an application-layer or managed load balancer when you need connection draining, rapid per-request health decisions, sticky sessions, protocol-aware routing, WebSocket control, rate limiting, circuit breaking, or balancing based on live capacity. DNS cannot see an individual request after it has returned an address.
Use a shared session store, stateless tokens, or deliberate session replication when users can move between endpoints. Otherwise a user may authenticate on one server and then lose state when the next connection reaches another.
Keep DNS routing simple when all endpoints are equivalent and the main requirement is regional or infrastructure redundancy. Choose health-aware routing when an unhealthy endpoint must be suppressed automatically. Choose priority or active/standby routing when only one site should receive traffic normally. Choose weighted, latency, or geographic policies only when you can operate and test the additional rules.
Operational checklist
- At least two endpoints exist in independent failure domains.
- Every endpoint serves the same hostname, certificate, application contract, and security policy.
- A health path checks the dependencies required for useful traffic.
- Probe protocol, port, timeout, interval, status, content, and thresholds are documented.
- Routing policy and all-unhealthy fallback behavior are explicit.
- TTL is selected against a measured recovery objective, not treated as a propagation guarantee.
- Authoritative and recursive DNS responses are monitored separately.
- Planned maintenance uses draining or endpoint disablement rather than abrupt deletion where possible.
- Failure, dependency outage, timeout, all-primary failure, recovery, and failback tests have been completed.
- Provider plan limits, health-check scope, geographic coverage, session-affinity options, observability, and current pricing have been verified in the provider’s current documentation.
Bottom line: the reliable configuration
Publish one A or AAAA record per equivalent endpoint only when every endpoint can serve the shared hostname. For genuine high availability, put those endpoints behind health-aware DNS routing—such as Route 53 health checks, Cloudflare Load Balancing pools and monitors, or Azure Traffic Manager probes—then define a tested fallback for the case where every primary is unhealthy. Choose a TTL that balances resolver load with your recovery objective, and validate the full chain from probe detection through recursive caching and client reconnection. DNS can direct new connections away from a failed endpoint; it cannot make cached answers, existing sessions, or stateful applications fail over instantly.
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