configuring flannel to use a non default interface in kubernetes

Question

Is there a way to define in which interface Flannel should be listening? According to his documentation adding FLANNEL_OPTIONS="--iface=enp0s8" in /etc/sysconfig/flanneld should work, but it isn't.

My master node configuration is running in a xenial(ubuntu 16.04) vagrant:

$ sudo kubeadm init --pod-network-cidr 10.244.0.0/16 --apiserver-advertise-address 10.0.0.10 

$ kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
clusterrole "flannel" created                                                                    
clusterrolebinding "flannel" created                                                                   
serviceaccount "flannel" created                                                                 
configmap "kube-flannel-cfg" created                                                                                                                                                       
daemonset "kube-flannel-ds" created   


ubuntu@master:~$ kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/k8s-manifests/kube-flannel-rbac.yml
clusterrole "flannel" configured                                                          
clusterrolebinding "flannel" configured         

Host ip addresses:

$ ip addr                      
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1     
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00                                    
    inet 127.0.0.1/8 scope host lo            
       valid_lft forever preferred_lft forever                                               
    inet6 ::1/128 scope host                  
       valid_lft forever preferred_lft forever                                               
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000                                                                                    
    link/ether 02:63:8e:2c:ef:cd brd ff:ff:ff:ff:ff:ff                                       
    inet 10.0.2.15/24 brd 10.0.2.255 scope global enp0s3                                     
       valid_lft forever preferred_lft forever                                               
    inet6 fe80::63:8eff:fe2c:efcd/64 scope link                                              
       valid_lft forever preferred_lft forever                                               
3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000                                                                                    
    link/ether 08:00:27:fb:ad:bb brd ff:ff:ff:ff:ff:ff                                       
    inet 10.0.0.10/24 brd 10.0.0.255 scope global enp0s8                                     
       valid_lft forever preferred_lft forever                                               
4: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default                                                                                            
    link/ether 02:42:da:aa:6e:13 brd ff:ff:ff:ff:ff:ff                                       
    inet 172.17.0.1/16 scope global docker0   
       valid_lft forever preferred_lft forever                                               
5: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default                                                                                         
    link/ether 5e:07:a1:7f:97:53 brd ff:ff:ff:ff:ff:ff                                       
    inet 10.244.0.0/32 scope global flannel.1 
       valid_lft forever preferred_lft forever                                               
    inet6 fe80::5c07:a1ff:fe7f:9753/64 scope link                                            
       valid_lft forever preferred_lft forever                                               
6: cni0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000                                                                                     
    link/ether 0a:58:0a:f4:00:01 brd ff:ff:ff:ff:ff:ff                                       
    inet 10.244.0.1/24 scope global cni0      
       valid_lft forever preferred_lft forever                                               
    inet6 fe80::7037:fcff:fe41:b1fb/64 scope link                                            
       valid_lft forever preferred_lft forever                  

Pods names:

$ kubectl get pods --all-namespaces                                                                                                                                         
NAMESPACE     NAME                             READY     STATUS              RESTARTS   AGE  
kube-system   etcd-master                      1/1       Running             0          2m   
kube-system   kube-apiserver-master            1/1       Running             0          2m   
kube-system   kube-controller-manager-master   1/1       Running             0          2m   
kube-system   kube-dns-545bc4bfd4-gjjth        0/3       ContainerCreating   0          3m   
kube-system   kube-flannel-ds-gdz8f            1/1       Running             0          1m   
kube-system   kube-flannel-ds-h4fd2            1/1       Running             0          33s  
kube-system   kube-flannel-ds-rnlsz            1/1       Running             1          33s  
kube-system   kube-proxy-d4wv9                 1/1       Running             0          33s  
kube-system   kube-proxy-fdkqn                 1/1       Running             0          3m   
kube-system   kube-proxy-kj7tn                 1/1       Running             0          33s  
kube-system   kube-scheduler-master            1/1       Running             0          2m   

Flannel Logs:

$ kubectl logs -n kube-system kube-flannel-ds-gdz8f -c kube-flannel
I1216 12:00:35.817207       1 main.go:474] Determining IP address of default interface
I1216 12:00:35.822082       1 main.go:487] Using interface with name enp0s3 and address 10.0.2.15
I1216 12:00:35.822335       1 main.go:504] Defaulting external address to interface address (10.0.2.15)
I1216 12:00:35.909906       1 kube.go:130] Waiting 10m0s for node controller to sync
I1216 12:00:35.909950       1 kube.go:283] Starting kube subnet manager
I1216 12:00:36.987719       1 kube.go:137] Node controller sync successful
I1216 12:00:37.087300       1 main.go:234] Created subnet manager: Kubernetes Subnet Manager - master
I1216 12:00:37.087433       1 main.go:237] Installing signal handlers
I1216 12:00:37.088836       1 main.go:352] Found network config - Backend type: vxlan
I1216 12:00:37.089018       1 vxlan.go:119] VXLAN config: VNI=1 Port=0 GBP=false DirectRouting=false
I1216 12:00:37.295988       1 main.go:299] Wrote subnet file to /run/flannel/subnet.env
I1216 12:00:37.296025       1 main.go:303] Running backend.
I1216 12:00:37.296048       1 main.go:321] Waiting for all goroutines to exit
I1216 12:00:37.296084       1 vxlan_network.go:56] watching for new subnet leases

How do I do to configure flannel in kubernetes to listen in enp0s8 instead of enp0s3?

Answer 1

I've the same problem, trying to use k8s and Vagrant. I've found this note in the documentation of flannel:

Vagrant typically assigns two interfaces to all VMs. The first, for which all hosts are assigned the IP address 10.0.2.15, is for external traffic that gets NATed.

This may lead to problems with flannel. By default, flannel selects the first interface on a host. This leads to all hosts thinking they have the same public IP address. To prevent this issue, pass the --iface eth1 flag to flannel so that the second interface is chosen.

So I look for it in the flannel's pod configuration. If you download the kube-flannel.yml file, you should look at DaemonSet spec, specifically at the "kube-flannel" container. There, you should add the required "--iface=enp0s8" argument (Don't forget the "="). Part of the code I've used.

  containers:
  - name: kube-flannel
    image: quay.io/coreos/flannel:v0.10.0-amd64
    command:
    - /opt/bin/flanneld
    args:
    - --ip-masq
    - --kube-subnet-mgr
    - --iface=enp0s8

Then run kubectl apply -f kube-flannel.yml

Hope helps.