Secondary DNS Instances

Secondary DNS instances receive zone data from primary servers via zone transfers (AXFR/IXFR). They provide redundancy and load distribution for DNS queries.

Creating a Secondary Instance

apiVersion: bindy.firestoned.io/v1alpha1
kind: Bind9Instance
metadata:
  name: secondary-dns
  namespace: dns-system
  labels:
    dns-role: secondary
    environment: production
spec:
  replicas: 1
  version: "9.18"
  config:
    recursion: false
    allowQuery:
      - "0.0.0.0/0"

Apply with:

kubectl apply -f secondary-instance.yaml

Key Differences from Primary

No Zone Transfers Allowed

Secondary servers typically don’t allow zone transfers:

spec:
  config:
    allowTransfer: []  # Empty or omitted - no transfers from secondary

Read-Only Zones

Secondaries receive zone data from primaries and cannot be updated directly. All zone modifications must be made on the primary server.

Label for Selection

Use the role: secondary label to enable automatic zone transfer configuration:

metadata:
  labels:
    role: secondary      # Required for automatic discovery
    cluster: production  # Required - must match cluster name

Important: The role: secondary label is required for Bindy to automatically discover secondary instances and configure zone transfers on primary zones.

Configuring Secondary Zones

When creating a DNSZone resource for secondary zones, use the secondary type and specify primary servers:

apiVersion: bindy.firestoned.io/v1alpha1
kind: DNSZone
metadata:
  name: example-com-secondary
  namespace: dns-system
spec:
  zoneName: example.com
  type: secondary
  instanceSelector:
    matchLabels:
      dns-role: secondary
  secondaryConfig:
    primaryServers:
      - "10.0.1.10"  # IP of primary DNS server
      - "10.0.1.11"  # Additional primary for redundancy

Automatic Zone Transfer Configuration

New in v0.1.0: Bindy automatically configures zone transfers from primaries to secondaries!

When you create primary DNSZone resources, Bindy automatically:

1. Discovers secondary instances using the role=secondary label
2. Configures zone transfers on primary zones with also-notify and allow-transfer
3. Tracks secondary IPs in DNSZone.status.secondaryIps
4. Detects IP changes when secondary pods restart or are rescheduled
5. Auto-updates zones when secondary IPs change (within 5-10 minutes)

Example:

# Create secondary instance with proper labels
cat <<EOF | kubectl apply -f -
apiVersion: bindy.firestoned.io/v1alpha1
kind: Bind9Instance
metadata:
  name: secondary-dns
  namespace: dns-system
  labels:
    role: secondary          # Required for discovery
    cluster: production      # Must match cluster name
spec:
  replicas: 2
  version: "9.18"
  config:
    recursion: false
EOF

# Create primary zone - zone transfers auto-configured!
cat <<EOF | kubectl apply -f -
apiVersion: bindy.firestoned.io/v1alpha1
kind: DNSZone
metadata:
  name: example-com
  namespace: dns-system
spec:
  zoneName: example.com
  clusterRef: production  # Matches cluster label
  # ... other config ...
EOF

# Verify automatic configuration
kubectl get dnszone example-com -n dns-system -o jsonpath='{.status.secondaryIps}'
# Output: ["10.244.1.5","10.244.2.8"]

Self-Healing: When secondary pods restart and get new IPs:

• Bindy detects the change within one reconciliation cycle (~5-10 minutes)
• Primary zones are automatically updated with new secondary IPs
• Zone transfers resume automatically with no manual intervention

Verifying Zone Transfers

Check that zones are being transferred:

# Check zone files on secondary
kubectl exec -n dns-system deployment/secondary-dns -- ls -la /var/lib/bind/zones/

# Check BIND9 logs for transfer messages
kubectl logs -n dns-system -l instance=secondary-dns | grep "transfer of"

# Verify secondary IPs are configured on primary zones
kubectl get dnszone -n dns-system -o yaml | yq '.items[].status.secondaryIps'

Best Practices

Use Multiple Secondaries

Deploy secondary instances in different locations:

# Secondary in different AZ/region
metadata:
  labels:
    dns-role: secondary
    region: us-west-1

Configure NOTIFY

Primary servers send NOTIFY messages to secondaries when zones change. Ensure network connectivity allows these notifications.

Monitor Transfer Status

Watch for failed transfers in logs:

kubectl logs -n dns-system -l instance=secondary-dns --tail=100 | grep -i transfer

Network Requirements

Secondaries must be able to:

1. Receive zone transfers from primaries (TCP port 53)
2. Receive NOTIFY messages from primaries (UDP port 53)
3. Respond to DNS queries from clients (UDP/TCP port 53)

Ensure Kubernetes network policies and firewall rules allow this traffic.

Next Steps

• Configure Multi-Region Setup with geographically distributed secondaries
• Create Secondary Zones that transfer from primaries
• Monitor DNS Infrastructure