Route 53 — Amazon Route 53

AWS docs: https://docs.aws.amazon.com/Route53/latest/APIReference/Welcome.html

Route 53 is served as a REST-XML API under the /2013-04-01/ path. Hosted zones, resource record sets, tags, and health checks are real metadata with AWS-faithful validation rules, error codes, defaults, auto-created child records, and pagination. Health check probes are still never sent — see “Known divergences” below — but DNS queries are answered: Overcast’s own internal resolver (internal/dns, OVERCAST_DNS/OVERCAST_DNS_PORT, see container-networking.md) is authoritative for any hosted zone in the store, in addition to the split-horizon emulator hostnames it already served.

DNS serving

• What’s served. For a query whose name falls under a hosted zone (the apex or any subdomain), the resolver answers from that zone’s record sets: A, AAAA, CNAME (chased across zones, up to 8 hops, with a cycle terminating the chain rather than looping), MX, TXT, NS, and SOA — including the apex NS/SOA records every zone gets on creation. One-label wildcard records (*.example.com) are matched exactly as real AWS scopes them: a wildcard replaces exactly one label, so *.example.com answers foo.example.com but not foo.bar.example.com. TTLs come from the record’s own stored TTL, not the split-horizon default. ALIAS records resolve to Overcast’s own address — the one the calling container or host can actually reach — since that is the only correct answer for an alias pointed at an emulated ELB/CloudFront/S3-website/API Gateway hostname in this environment; an AAAA-typed alias has no address to give (Overcast has no IPv6 address) and answers NODATA. A name that exists in the zone but has no record of the queried type is NODATA; a name absent from the zone entirely is NXDOMAIN; both carry the zone’s SOA in the authority section for negative caching. NAPTR/PTR/SRV/SPF/CAA/DS/TLSA/SSHFP/SVCB/HTTPS records can be stored via ChangeResourceRecordSets but are not served — a query for one of them gets NODATA/NXDOMAIN like any other type absent at that name.
• How a Route 53 zone interacts with the container-name resolver. These are two independent authorities the same resolver consults, checked in order: a name some hosted zone in the store claims is answered from that zone first and always authoritatively (never forwarded, even if it also happens to fall under one of Overcast’s own split-horizon domains); only a name no hosted zone claims falls through to the split-horizon zone/forwarding behaviour internal/dns’s package doc describes. A container-endpoint name (an RDS endpoint, an ElastiCache node) is still resolved by Docker’s embedded resolver from the container’s network aliases before either authority is reached — see container-networking.md — so it is unaffected by this feature either way.
• Private zones and VPC association. Real Route 53 only serves a private hosted zone’s records to a resolver inside one of the zone’s associated VPCs. Overcast does not model “inside a VPC” as a property of a DNS query — AssociateVPCWithHostedZone/DisassociateVPCFromHostedZone are not implemented at all (see below) — so, kept deliberately honest and simple, every container Overcast starts is answered from every private zone the store holds, with no VPC filtering. When a public and a private zone share the same name, the private zone wins. This can only make more names resolve in the emulator than would on real AWS, never fewer, for a container correctly associated with the zone’s VPC.
• Public zones and host resolution. The emulator’s DNS resolver is consulted only by the containers Overcast starts (pointed at it via Docker’s embedded resolver) and by a host that has explicitly pointed its own resolution at Overcast. Overcast never attempts to become an internet-reachable authority for a public zone’s real domain name — there is no NS delegation, no port 53 published to the internet, nothing that would let it answer for anyone but its own containers and an opted-in host.

Behavior Notes

• Route 53 is treated as a global service in this emulator.
• Hosted zone IDs are stored and returned in AWS-style path format, for example /hostedzone/Z123...; change IDs likewise (/change/C123...).
• Errors use Route 53’s ErrorResponse envelope (Type/Code/Message), not S3’s bare <Error> shape.
• CreateHostedZone requires a CallerReference and rejects a reused one with HostedZoneAlreadyExists (HTTP 409). Each new zone gets the default apex NS and SOA record sets and a four-server delegation set, derived deterministically from the zone ID. The new zone’s URL is returned in the Location header, as on real AWS.
• Domain and record names are canonicalised to lowercase with a trailing dot.
• ChangeResourceRecordSets validates the whole batch atomically before applying anything: InvalidChangeBatch for creating an existing record, deleting a missing record or one whose provided values don’t match, records outside the zone, a CNAME at the zone apex, and deleting the default apex NS/SOA records. Weighted/latency/failover/geolocation routing metadata (SetIdentifier, Weight, Region, Failover, GeoLocation, MultiValueAnswer, HealthCheckId) is stored and returned, but routing is not evaluated — including at DNS-answer time: several record sets sharing a name and type under different SetIdentifiers (weighted, multivalue, failover) are all merged into the same answer rather than one being chosen.
• ListResourceRecordSets returns records in DNS order (names compared with labels reversed) and paginates with name/type/identifier/maxitems.
• DeleteHostedZone returns HostedZoneNotEmpty while non-default records exist; a successful delete cascades the default records and the zone’s tags.
• Health checks are metadata-only: configuration is stored with AWS defaults (RequestInterval 30, FailureThreshold 3, port 80/443 by type) and versioned by UpdateHealthCheck, but no endpoint is ever probed.

Known divergences

• ChangeResourceRecordSets applies synchronously, so change status is INSYNC immediately — there is no PENDING phase.
• GetChange reports INSYNC for unknown change IDs instead of NoSuchChange, so CDK/CLI waiters always converge (even across a store reset).
• Private hosted zones may be created without a VPC (real AWS requires one); the VPC passed to CreateHostedZone is stored and returned, but AssociateVPCWithHostedZone/DisassociateVPCFromHostedZone are not implemented.
• InvalidChangeBatch/InvalidInput message texts approximate AWS’s wording; codes and HTTP statuses match.
• DNS serving has no notion of “inside a VPC”: a private zone answers for every container Overcast starts rather than only ones associated with the zone’s VPC (see “Private zones and VPC association” above).
• Empty non-terminal names — a label with no records of its own but with records below it (e.g. querying mid.example.com when only leaf.mid.example.com has data) — are answered NXDOMAIN rather than the strictly correct NODATA, since the resolver does not enumerate implicit non-terminals; this only affects a query for the exact intermediate name, which is rare in practice.
• No compression is used in DNS answers beyond the question-name pointer the split-horizon fast path already used; a Route 53 answer with many large records could in principle exceed the 512-byte UDP-without-EDNS0 limit and need the TCP retry, which is otherwise unaffected.

Summary

Category	✅ Supported	❌ Unsupported
Hosted Zones	7
Resource Records	2
Change Management	1
Tags	3
Health Checks	6	2
Traffic Policies		1
VPC Associations		3

---

Endpoints

Hosted Zones

Operation	Status	Notes	AWS Docs
CreateHostedZone	✅ Supported		docs
ListHostedZones	✅ Supported		docs
ListHostedZonesByName	✅ Supported		docs
GetHostedZone	✅ Supported		docs
GetHostedZoneCount	✅ Supported		docs
UpdateHostedZoneComment	✅ Supported		docs
DeleteHostedZone	✅ Supported		docs

Resource Records

Operation	Status	Notes	AWS Docs
ChangeResourceRecordSets	✅ Supported		docs
ListResourceRecordSets	✅ Supported		docs

Change Management

Operation	Status	Notes	AWS Docs
GetChange	✅ Supported		docs

Tags

Operation	Status	Notes	AWS Docs
ChangeTagsForResource	✅ Supported		docs
ListTagsForResource	✅ Supported		docs
ListTagsForResources	✅ Supported		docs

Health Checks

Operation	Status	Notes	AWS Docs
CreateHealthCheck	✅ Supported		docs
GetHealthCheck	✅ Supported		docs
ListHealthChecks	✅ Supported		docs
GetHealthCheckCount	✅ Supported		docs
UpdateHealthCheck	✅ Supported		docs
DeleteHealthCheck	✅ Supported		docs
GetHealthCheckStatus	❌ Unsupported		docs
GetHealthCheckLastFailureReason	❌ Unsupported		docs

Traffic Policies

Operation	Status	Notes	AWS Docs
CreateTrafficPolicy	❌ Unsupported		docs

VPC Associations

Operation	Status	Notes	AWS Docs
AssociateVPCWithHostedZone	❌ Unsupported		docs
DisassociateVPCFromHostedZone	❌ Unsupported		docs
ListHostedZonesByVPC	❌ Unsupported		docs