In this tutorial we deploy MetalLB in a cluster and announce a load-balanced IP using ARP. We assume you have a bare metal cluster already running, for example a Raspberry Pi Kubernetes cluster.
The nice thing about ARP mode is that you don’t need any fancy network hardware at all, it should just work on any ethernet network.
Here is the outline of what we’re going to do:
For this tutorial, we’ll assume the cluster is set up on a network
192.168.1.0/24. The main router is configured to hand out DHCP
address in the
We need to allocate another chunk of this IP space for MetalLB
services. We’ll use
192.168.1.240/28 (192.168.1.240 to
192.168.1.255) for this.
If your cluster is not using the same addresses, you’ll need to substitute the appropriate address ranges in the rest of this tutorial. We’ll point out the places where you need to make edits.
MetalLB runs in two parts: a cluster-wide controller, and a per-machine protocol speaker.
Install MetalLB by applying the manifest:
kubectl apply -f https://raw.githubusercontent.com/google/metallb/v0.3.0/manifests/metallb.yaml
This manifest creates a bunch of resources. Most of them are related to access control, so that MetalLB can read and write the Kubernetes objects it needs to do its job.
Ignore those bits for now, the two pieces of interest are the
“controller” deployment, and the “speaker” DaemonSet. Wait for these
to start by monitoring
kubectl get pods -n metallb-system.
Eventually, you should see some running pods.
controller-74d6b85f86-xw5mx 1/1 Running 0 32m speaker-kr2ks 1/1 Running 0 31m speaker-skfrp 1/1 Running 0 31m speaker-zmtb4 1/1 Running 0 32m
You should see one controller pod, and one speaker pod for each node in your cluster.
Your pods will have a slightly different names, because the suffix is randomly generated.
Nothing has been announced yet, because we didn’t supply a ConfigMap, nor a service with a load-balanced address.
We have a sample MetalLB configuration in
Let’s take a look at it before applying it:
apiVersion: v1 kind: ConfigMap metadata: namespace: metallb-system name: config data: config: | address-pools: - name: my-ip-space protocol: arp cidr: - 192.168.1.240/28
If you used different IP addresses in your cluster, change the IP range in this configuration before applying it.
MetalLB’s configuration is a standard Kubernetes ConfigMap,
metallb-system namespace. It contains two pieces of
information: what IP addresses it’s allowed to hand out and which
protocol to do that with.
In this configuration we tell MetalLB to hand out address from the
192.168.1.240/28 range, using ARP (
protocol: arp). Apply this
kubectl apply -f https://raw.githubusercontent.com/google/metallb/v0.3.0/manifests/example-arp-config.yaml
The configuration should take effect within a few seconds. By
following the logs we can see what’s going on:
kubectl logs -l
app=speaker -n metallb-system:
I1217 10:18:05.212018 1 leaderelection.go:174] attempting to acquire leader lease... I1217 10:18:07.312902 1 bgp_controller.go:176] Start config update I1217 10:18:07.403537 1 bgp_controller.go:243] End config update I1217 10:18:07.403748 1 arp_controller.go:128] Start config update I1217 10:18:07.403883 1 arp_controller.go:143] End config update
The speaker has loaded the configuration, but hasn’t done anything else yet, because there are no LoadBalancer services in the cluster.
a trivial service: an nginx pod, and a load-balancer service pointing
at nginx. Deploy it to the cluster:
kubectl apply -f https://raw.githubusercontent.com/google/metallb/v0.3.0/manifests/tutorial-2.yaml
Wait for nginx to start by monitoring
kubectl get pods, until you
see a running nginx pod. It should look something like this:
NAME READY STATUS RESTARTS AGE nginx-558d677d68-j9x9x 1/1 Running 0 47s
Once it’s running, take a look at the
nginx service with
get service nginx:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE nginx LoadBalancer 10.102.30.250 192.168.1.240 80:31517/TCP 1d
We have an external IP! Looking through the logs of
speaker we see it happening:
I1217 10:18:07.409788 1 arp_controller.go:53] default/nginx: start update I1217 10:18:07.409867 1 arp_controller.go:96] default/nginx: announcable, making advertisement I1217 10:18:07.409977 1 arp_controller.go:107] default/nginx: end update ... I1217 10:19:01.905426 1 leader.go:61] Sending unsolicited ARPs for 1 addresses I1217 10:19:05.005671 1 arp.go:96] Request: who-has 192.168.1.240? tell 192.168.1.1 (b4:75:0e:63:b2:20). reply: 192.168.1.240 is-at b8:27:eb:86:e2:85 I1217 10:19:05.105780 1 arp.go:96] Request: who-has 192.168.1.240? tell 192.168.1.1 (b4:75:0e:63:b2:20). reply: 192.168.1.240 is-at b8:27:eb:86:e2:85 I1217 10:19:05.235623 1 arp.go:96] Request: who-has 192.168.1.240? tell 192.168.1.1 (b4:75:0e:63:b2:20). reply: 192.168.1.240 is-at b8:27:eb:86:e2:85
MetalLB is sending out unsolicited ARP responses and replies to ARP requests with the MAC address of the node that has won the master election. It is using the first address of the assigned range (192.168.1.240).
curl http://192.168.1.240 you should see the default nginx
page: “Welcome to nginx!”