MetalLB on Kubernetes, via Helm

MetalLB offers a network load balancer implementation which workes on "bare metal" (as opposed to a cloud provider).

MetalLB does two jobs:

1. Provides address allocation to services out of a pool of addresses which you define
2. Announces these addresses to devices outside the cluster, either using ARP/NDP (L2) or BGP (L3)

L3 vs L2

MetalLB can be configured to operate in either Layer 2 or Layer 3 mode (below). See my highly accurate and technically appropriate diagrams below to understand the difference:

Layer 3 (recommended)

When configuring MetalLB for Layer 3, you define a dedicated subnet to be advertised from your MetalLB pods to your BGP-speaking router/firewall. This subnet shouldn't be configured on any nodes, or any of your network equipment. We are taking advantage of a protocol first designed in 1989 to allow MetalLB to tell your router where to send traffic to this new subnet (it should send it to the Kubernetes nodes, of course, which are on the same network as the router already is).

If you need to access your services externally, then perform NAT on your firewall to the external IP assigned to your LoadBalancerIP Kubernetes service by MetalLB.

Use BGP if possible - it's far easier to debug / monitor than Layer 2 (below)

Layer 2

Now we are taking advantage of a protocol first designed in 1982 to "lie to" other devices on your subnet, telling them that the MAC address for a given IP belongs whichever MetalLB pod has the "leader" role for this virtual IP.

As above, if you need to access your services externally, then perform NAT on your firewall to the external IP assigned to your LoadBalancerIP Kubernetes service by MetalLB.

Use Layer 2 if your firewall / router can't support BGP.

MetalLB Requirements

Allocations

You'll need to make some decisions re IP allocations.

• What is the range of addresses you want to use for your LoadBalancer service pool? If you're using BGP, this can be a dedicated subnet (i.e. a /24), and if you're not, this should be a range of IPs in your existing network space for your cluster nodes (i.e., 192.168.1.100-200)
• If you're using BGP, pick two private AS numbers between 64512 and 65534 inclusively.

Namespace

We need a namespace to deploy our HelmRelease and associated ConfigMaps into. Per the flux design, I create this example yaml in my flux repo:

apiVersion: v1
kind: Namespace
metadata:
  name: metallb-system

HelmRepository

Next, we need to define a HelmRepository (a repository of helm charts), to which we'll refer when we create the HelmRelease. We only need to do this once per-repository. In this case, we're using the (prolific) metallb chart repository, so per the flux design, I create this example yaml in my flux repo:

apiVersion: source.toolkit.fluxcd.io/v1beta2
kind: HelmRepository
metadata:
  name: metallb
  namespace: flux-system
spec:
  interval: 15m
  url: https://metallb.github.io/metallb

Kustomization

Now that the "global" elements of this deployment (Namespace and HelmRepository) have been defined, we do some "flux-ception", and go one layer deeper, adding another Kustomization, telling flux to deploy any YAMLs found in the repo at /metallb-system. I create this example Kustomization in my flux repo:

apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: metallb--metallb-system
  namespace: flux-system
spec:
  interval: 15m
  path: ./metallb-system
  prune: true # remove any elements later removed from the above path
  timeout: 2m # if not set, this defaults to interval duration, which is 1h
  sourceRef:
    kind: GitRepository
    name: flux-system
  healthChecks:
    - apiVersion: apps/v1
      kind: Deployment
      name: metallb-controller
      namespace: metallb-system

ConfigMap (for HelmRelease)

Now we're into the metallb-specific YAMLs. First, we create a ConfigMap, containing the entire contents of the helm chart's values.yaml. Paste the values into a values.yaml key as illustrated below, indented 4 spaces (since they're "encapsulated" within the ConfigMap YAML). I create this example yaml in my flux repo at ``:

apiVersion: v1
kind: ConfigMap
metadata:
  name: metallb-helm-chart-value-overrides
  namespace: metallb-system
data:
  values.yaml: |-  # (1)!
    # <upstream values go here>

1. Paste in the contents of the upstream values.yaml here, intended 4 spaces, and then change the values you need as illustrated below.

Then work your way through the values you pasted, and change any which are specific to your configuration.

Kustomization for CRs (Config)

Older versions of MetalLB were configured by a simple ConfigMap, which could be deployed into Kubernetes alongside the helmrelease, since a ConfigMap is a standard Kubernetes primitive.

Since v0.13 though, MetalLB is configured exclusively using CRDs (this allows for syntax validation, among other advantages). This means that the custom resources (CRs) have to be applied after MetalLB's helm chart has been deployed, since it's the chart which creates the CRD definitions. So we can't deploy the config CRs in the same kustomization as we deploy the helmrelease (because the CRDs won't exist yet!)

The simplest way to solve this chicken-and-egg problem is to create a second Kustomization for the MetalLB CRs, and make it depend on the first Kustomization (MetalLB itself).

I create this example Kustomization in my flux repo:

apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: config--metallb-system
  namespace: flux-system
spec:
  interval: 15m
  dependsOn: # (1)!
  - name: metallb--metallb-system  
  path: ./metallb-config
  prune: true # remove any elements later removed from the above path
  timeout: 2m # if not set, this defaults to interval duration, which is 1h
  sourceRef:
    kind: GitRepository
    name: flux-system
  healthChecks:
    - apiVersion: apps/v1
      kind: Deployment
      name: metallb-controller
      namespace: metallb-system

1. The dependsOn key will prevent Flux from trying to reconcile this Kustomization until the kustomizations it depends on, have successfully reconcilled.

Custom Resources

Finally, it's time to actually configure MetalLB! In my setup, I'm using BGP against a pair of pfsense¹ firewalls, so per the official docs, I use the following configurations, saved in my flux repo:

IPAddressPool

apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
  name: metallb-pool
  namespace: metallb-system
spec:
  addresses:
  - 192.168.32.0/24

BGPAdvertisment

apiVersion: metallb.io/v1beta1
kind: BGPAdvertisement
metadata:
  name: metallb-advertisment
  namespace: metallb-system
spec:
  ipAddressPools:
  - metallb-pool # (1)!
  aggregationLength: 32
  localPref: 100
  communities:
  - 65535:65282

1. This must be the same as the name of the IPAddressPool defined above

BGPPeer(s)

You need separate BGPPeer resource for every BGP peer, from MetalLB's perspective. Because I use dual pfsense firewalls, I maintain two files, each identifying its peer in its filename, like this:

apiVersion: metallb.io/v1beta2
kind: BGPPeer
metadata:
  name: bgppeer-192.168.33.2
  namespace: metallb-system
spec:
  myASN: 64500
  peerASN: 64501
  peerAddress: 192.168.33.2

Summary

In the config referenced above, I define one pool of addresses (192.168.32.0/24) which MetalLB is responsible for allocating to my services. MetalLB will then "advertise" these addresses to my firewalls (192.168.33.2 and 192.168.33.4), in an eBGP relationship where the firewalls' ASN is 64501 and MetalLB's ASN is 64500.

Provided I'm using my firewalls as my default gateway (a VIP), when I try to access one of the 192.168.32.x IPs from any subnet connected to my firewalls, the traffic will be routed from the firewall to one of the cluster nodes running the pods selected by that service.

apiVersion: metallb.io/v1beta1
kind: L2Advertisement
metadata:
  name: my-l2-advertisment
  namespace: metallb-system
spec:
  ipAddressPools:
  - metallb-pool # (1)!

HelmRelease

Lastly, having set the scene above, we define the HelmRelease which will actually deploy MetalLB into the cluster, with the config and extra ConfigMap we defined above. I save this in my flux repo:

apiVersion: helm.toolkit.fluxcd.io/v2beta1
kind: HelmRelease
metadata:
  name: metallb
  namespace: metallb-system
spec:
  chart:
    spec:
      chart: metallb
      version: 0.13.7
      sourceRef:
        kind: HelmRepository
        name: metallb
        namespace: flux-system
  interval: 15m
  timeout: 5m
  releaseName: metallb
  valuesFrom:
  - kind: ConfigMap
    name: metallb-helm-chart-value-overrides
    valuesKey: values.yaml # This is the default, but best to be explicit for clarity

Deploy MetalLB

Having committed the above to your flux repository, you should shortly see a metallb kustomization, and in the metallb-system namespace, a controller and a speaker pod for every node:

root@cn1:~# kubectl get pods -n metallb-system -o wide
NAME                                  READY   STATUS    RESTARTS   AGE   IP              NODE   NOMINATED NODE   READINESS GATES
metallb-controller-779d8686f6-mgb4s   1/1     Running   0          21d   10.0.6.19       wn3    <none>           <none>
metallb-speaker-2qh2d                 1/1     Running   0          21d   192.168.33.24   wn4    <none>           <none>
metallb-speaker-7rz24                 1/1     Running   0          21d   192.168.33.22   wn2    <none>           <none>
metallb-speaker-gbm5r                 1/1     Running   0          21d   192.168.33.23   wn3    <none>           <none>
metallb-speaker-gzgd2                 1/1     Running   0          21d   192.168.33.21   wn1    <none>           <none>
metallb-speaker-nz6kd                 1/1     Running   0          21d   192.168.33.25   wn5    <none>           <none>
root@cn1:~#

- key: "node-role.kubernetes.io/master"
  effect: "NoSchedule"

How do I know it's working?

If you used my template repository to start off your flux deployment strategy, then the podinfo helm chart has already been deployed. By default, the podinfo service is in ClusterIP mode, so it's only reachable within the cluster.

Edit your podinfo helmrelease configmap (/podinfo/configmap-podinfo-helm-chart-value-overrides.yaml), and change this:

    <snip>
    # Kubernetes Service settings
    service:
      enabled: true
      annotations: {}
      type: ClusterIP
    <snip>

To:

    <snip>
    # Kubernetes Service settings
    service:
      enabled: true
      annotations: {}
      type: LoadBalancer
    <snip>

Commit your changes, wait for a reconciliation, and run kubectl get services -n podinfo. All going well, you should see that the service now has an IP assigned from the pool you chose for MetalLB!

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