DNS resolver

The embedded DNS resolver provides authoritative bridge DNS for workloads when using the edgelet container engine. It maintains an in-memory workload registry, serves *.svc.bridge.local, optional docker/podman compatibility aliases, and forwards non-local queries upstream.

Code: internal/dnsresolver/

Operator guide: DNS

Purpose

• Register A/AAAA answers for microservice FQDNs on the bridge network
• Dual scope listeners: managed (edgelet) vs local deploy (iofog-local)
• Reconcile DNS records from runtime container snapshots
• Rate limiting, forwarding health, metrics snapshot for status/metrics endpoints
• Reserved names: agent, router, NATS, ControlPlane FQDNs

Dependencies

Depends on	Reason
network	Bridge gateway IP per scope
config	Feature flags, intervals, upstreams

Used by	Reason
pkg/engine/edgelet	Primary upsert/remove on container lifecycle
processmanager	ControlPlane workload DNS upsert
pkg/docker	ExtraHosts / network aliases for docker engine
edgeletapi/handlers	Status DNS health, Prometheus metrics

Architecture

Singleton: dnsresolver.GetInstance() → *Resolver.

Default zone: svc.bridge.local.

Scopes

Scope	Constant	Typical workloads
Managed	ScopeManaged (edgelet)	Controller-managed MS
Local	ScopeLocal (iofog-local)	CLI deploy, ControlPlane

Agent DNS: edgelet.default.svc.bridge.local.

Lifecycle

Resolver starts when edgelet engine initializes (Engine.Init wires GetInstance()). Background workers:

• Reconcile loop. Sync registry from runtime snapshot (default 60s)
• Snapshot/stats. Counters for queries, NXDOMAIN, rate limits
• Bind retry. Retry listener bind every 5s on failure

Not a Supervisor module with its own Start(). Owned by engine lifecycle.

Record updates

UpsertWorkload(WorkloadRecord) / RemoveWorkload(uuid):

• Called from edgelet engine on container start/stop
• ControlPlane: processmanager/controlplane_dns.go
• Records include application, name, IP, flags (IsRouter, IsNats, IsController)

Helper: WorkloadBridgeNetworkAliases() for docker ExtraHosts parity.

Configuration

Resolver reads config for reconcile interval, rate limits, max request sizes, compat alias enablement, upstream forwarders. See DNS for operator-facing keys.

External APIs

Surface	Role
DNS UDP/TCP on bridge gateway	Workload queries
GET /v1/system/status	DNS health derived from snapshot
GET /metrics	DNS counters exported

Observability

• Log module: "EmbeddedDNS"
• StatsSnapshot: query totals, reconcile counts, forwarding degradation flags
• deriveDNSHealth() in status handler maps snapshot → health string

Failure modes

Symptom	Typical cause
NXDOMAIN for valid MS	Reconcile lag; container not registered
Forwarding degraded	Upstream DNS unreachable
CP names missing	controlplane_dns upsert not run

Code map

File	Role
resolver.go	Core server, registry, listeners
reconcile.go	Periodic snapshot reconcile
snapshot.go	Stats snapshot for status/metrics
forwarding.go	Upstream DNS forward
controlplane.go	ControlPlane FQDN helpers
ratelimit.go	Query rate limiting

Related: Engines, Process manager, DNS.

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