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While this loads — worth knowing
ElastiCache RedisnotElastiCache Memcached
Redis has data structures — sorted sets, counters, pub/sub. Memcached has plain keys and nothing else.
Loading…
While this loads — worth knowing
Redis has data structures — sorted sets, counters, pub/sub. Memcached has plain keys and nothing else.
AWS's DNS service. It registers domains, answers queries for them with a choice of routing policies, and sends traffic away from endpoints that fail their health checks.
Where Route 53 takes you6 steps, all open
Route 53 is AWS's DNS service. It does three jobs, in any combination: it registers domain names, it answers DNS queries for them, and it checks the health of the endpoints behind them.
A hosted zone holds a domain's records. A public hosted zone answers queries from the internet; a private hosted zone answers only inside the VPCs you associate with it. Each record has a routing policy, which decides how Route 53 answers when there is more than one place to send someone.
You ask the directory for a business's number. The operator can give you the nearest branch, the branch for your country, a number picked by shares the business chose, or the backup branch when the main one is not answering. You write the number down, and do not ask again until your note expires.
Hosted zoneRecordRouting policyHealth checkTTLPrivate hosted zoneA zone that can answer for the domain. A private zone answers only inside the VPCs associated with it.
The records with this name and type.
Chooses among them: by weight, by latency, by location, or primary before secondary.
A record whose health check is failing is left out of the answer.
The resolver caches it for the TTL. An alias to an AWS resource uses that resource's TTL.
Pick a case to follow the query through each check.
Both are failover alias records for example.com, one primary and one secondary, each pointing at a load balancer. An alias can sit at the zone apex, where a CNAME cannot.
With Evaluate Target Health set to Yes, each alias record takes its health from the load balancer it points at, so no separate health check is created for it. AWS recommends exactly that for any resource an alias can point at.
Failover records with health checks, TTL 60 seconds
UsersServed by Primary site
Click a node to make it fail. The timings in the log are the real ones, played 25× faster.
Where the time goes. Health checkers need three failures in a row, 30 seconds apart by default, before the primary is unhealthy: about 90 seconds. Then resolvers that cached the old answer keep handing it out until its TTL runs out, 60 seconds here. A shorter TTL fails over sooner and sends Route 53 more queries.
Faster checks cost more. A 10-second interval finds the failure sooner, at extra charge.
Checking what cannot be reached. Health checkers cannot test an address in a private range. For a private resource, base the health check on a CloudWatch alarm instead.
Private hosted zones keep internal names internal. They answer only in the VPCs associated with them. From anywhere else the query goes to the public internet, where those names do not exist.
Resolver DNS Firewall filters the DNS queries your VPCs make, with domain lists and rules you write, so an instance cannot look up a domain you have blocked.
Changing a record is an IAM permission. Whoever can edit the records decides where your users go, so grant it as narrowly as any other.
Hosted zones, by the month, with an extra charge for records beyond a standard number.
Queries. Latency, geolocation and IP-based queries cost more than standard ones. Queries for alias records that point at AWS resources, such as load balancers, CloudFront and S3 website endpoints, are free. A CNAME query is charged, and one that points to another Route 53 record is charged as two.
Health checks, with more for endpoints outside AWS and for HTTPS, string matching and the 10-second interval.
Domains, by the year, at a price that depends on the top-level domain.
Prices change, so none are printed here. Check the Route 53 pricing page on aws.amazon.com.
| Policy | Answers with | Choose it when |
|---|---|---|
| Simple | The one resource | One resource does the job |
| Weighted | Resources in the proportions you set | Trying a new version on a share of the traffic |
| Latency | The Region with the best latency for the user | Resources in several Regions, users everywhere |
| Failover | The primary, or the secondary when the primary is unhealthy | Active-passive disaster recovery |
| Geolocation | The resource for the user's continent, country or US state | Language, or rights to show content only in some places |
| Geoproximity | Resources by their location, with traffic shifted between them if you choose | Moving traffic from one location of yours to another |
| IP-based | The resource for the address range the query comes from | You know the IP ranges your users come from |
| Multivalue answer | Up to eight healthy records, at random | Simple spreading, with health checks |
| Question | Alias record | CNAME record |
|---|---|---|
| Allowed at the zone apex, example.com | Yes | No |
| Points to | Selected AWS resources, or a record in the same zone | Any DNS name |
| Queries to AWS resources | Not charged | Charged |
| TTL | The target resource's, not yours to set | Yours to set |
| Shows in dig as | A or AAAA, the type you chose | CNAME |
point example.com, the zone apex, at a load balancerAn alias record
A CNAME cannot be created at the apex. An alias can, and its queries to AWS resources are free.
send users to the Region that responds fastest for themLatency routing
It answers with the Region that gives each user the best latency.
send a small share of traffic to the new versionWeighted routing
Each record gets its weight's share of the total. A weight of 0 stops traffic to it.
show the content only in countries where the company has the rightsGeolocation routing
It answers by the user's location. Without a default record, unmatched locations get no answer.
show a static maintenance page from S3 if the site goes downFailover routing, with the S3 website as the secondary
The secondary answers only when the primary is unhealthy.
resolve names like db.example.com only inside the VPCA private hosted zone
It answers only queries from the VPCs associated with it.
return several healthy IP addresses and let the client chooseMultivalue answer routing
Up to eight healthy records, picked at random.
health check an instance that has only a private IP addressA health check on a CloudWatch alarm
Route 53 health checkers cannot reach private addresses.
the health check failed quickly, but users kept going to the old siteThe TTL
Resolvers keep a cached answer until its TTL runs out.
A company runs its website in us-east-1 behind an Application Load Balancer. A copy in eu-west-1 should serve users only if the primary Region fails. The site is at the zone apex, example.com. What should a solutions architect configure in Route 53?
The company's domain is example.com, and at the apex it must point to an Application Load Balancer whose addresses change as it scales. The company wants the domain's DNS to run on AWS. What answers the DNS queries for example.com?
30 s, unhealthy after 3 failures, healthy when over 18% agree.This whole page is free right now.The AWS library is still being written, so every page of it is open to everyone while that lasts. It becomes a paid bundle later; what you read today costs you nothing.
Every fact on this page was checked against AWS’s own documentation on 15 Sept 2026. If AWS has changed something since, its page is the one to trust.