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Operations

Scope

Production deployment patterns, operational procedures, performance tuning, and troubleshooting for Flannel.

Deployment

Installation

# Apply Flannel manifest
kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml

Backend Selection

Backend Overhead Performance Encryption Use Case
VXLAN Medium Good No Default, most clusters
host-gw None Best No L2-adjacent nodes only
WireGuard Low Good Yes Cross-DC with encryption 
// net-conf.json
{
  "Network": "10.244.0.0/16",
  "Backend": {
    "Type": "vxlan",
    "VNI": 1,
    "DirectRouting": true
  }
}

Operations

# Check Flannel pods
kubectl get pods -n kube-flannel

# Check subnet allocation
cat /run/flannel/subnet.env

# Check VXLAN interface
ip -d link show flannel.1

Troubleshooting

Issue Diagnosis Fix
Pod network unreachable ip route show Check flannel.1 interface, VXLAN
Subnet conflict /run/flannel/subnet.env Delete flannel.1, restart pod
flanneld crash kubectl logs -n kube-flannel Check etcd connectivity
MTU issues ip link show flannel.1 Set MTU to 1450 (VXLAN overhead)

Commands & Recipes

Installation

# Install Flannel on K8s (standard)
kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml

# Install with custom CIDR
kubectl apply -f - <<EOF
kind: ConfigMap
apiVersion: v1
metadata:
  name: kube-flannel-cfg
  namespace: kube-flannel
data:
  net-conf.json: |
    {
      "Network": "10.244.0.0/16",
      "EnableIPv6": false,
      "Backend": {
        "Type": "vxlan"
      }
    }
EOF

Backend Configuration

// VXLAN (default)
{ "Type": "vxlan" }

// host-gw (best performance, requires same L2)
{ "Type": "host-gw" }

// WireGuard (encrypted)
{ "Type": "wireguard" }

Diagnostics

# Check flannel pods
kubectl get pods -n kube-flannel

# View subnet allocation
kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.podCIDR}{"\n"}{end}'

# Flannel logs
kubectl logs -n kube-flannel -l app=flannel -f

# Check VXLAN interface
ip -d link show flannel.1

# Check routes
ip route show | grep flannel

Sources