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Configuring Route Reflectors in Calico

Calico is a popular CNI plugin for Kubernetes. It leverages Border Gateway Protocol (BGP) for communicating routes available on nodes. This method fosters a highly scalable networking model between our workloads.

Click here to watch the video version of this content.

The Case for Route Reflection

Calico requires no additional routers or infrastructure to run. Like many CNI plugins, you can apply it using kubectl.

kubectl apply -f https://docs.projectcalico.org/v3.3/getting-started/kubernetes/installation/hosted/rbac-kdd.yaml
kubectl apply -f https://docs.projectcalico.org/v3.3/getting-started/kubernetes/installation/hosted/kubernetes-datastore/calico-networking/1.7/calico.yaml

Once started, Calico runs a node-to-node mesh. This means every node peers to every other node to broadcast routes. This is done from the calico/node pod that runs on every node (via a daemonset). Let's assume a 5 node cluster, with an IP range of 10.30.0.13-10.30.0.17.

Every colored line represents a peering connection we'd expect in this cluster. These connections can be surfaced by downloading calicoctl and running sudo calicoctl node status on a node. The example below shows the output from 10.30.0.15 in our example.

sudo calicoctl node status

Calico process is running.

IPv4 BGP status
+--------------+-------------------+-------+----------+--------------------------------+
| PEER ADDRESS |     PEER TYPE     | STATE |  SINCE   |              INFO              |
+--------------+-------------------+-------+----------+--------------------------------+
| 10.30.0.17   | node-to-node mesh | up    | 01:17:08 | Established                    |
| 10.30.0.16   | node-to-node mesh | up    | 01:17:07 | Established                    |
| 10.30.0.14   | node-to-node mesh | up    | 01:29:06 | Established                    |
| 10.30.0.13   | node-to-node mesh | up    | 01:29:06 | Established                    |
+--------------+-------------------+-------+----------+--------------------------------+

This default behavior prevents us from worrying about upstream routers and BGP-configuration complexity. However, once our cluster grows to hundreds of nodes, we may find this node-to-node mesh to be no longer scalable. Route reflectors provide a solution to this. Since Calico 3, calico/node can act as a reflector. Introducing 2 calico/node pods or containers as route reflectors would change the peering relationship to the following.

Calico makes achieving the above easy. We have 3 options to choose from.

  1. Dedicate Kubernetes node(s) to be route reflectors.

  2. Run calico/node as a container on non-Kubernetes host(s).

  3. Run a different reflector, such as a dedicated BIRD binary, and setup Calico to peer with it.

Trade-offs must be weighed between the options. Since configuration of option 1 & 2 are nearly identical and option 1 doesn't require additional hosts, we'll choose option 1 for demonstrating how reflection is configured. To do this we'll perform the following steps.

  1. Select and configure Node resources to act as reflectors.

  2. Setup BGPPeering configurations to talk to reflectors.

  3. Disable node-to-node mesh.

Configuring Nodes

First, we need to select the Nodes in our cluster to act as route reflectors. You may choose to taint these nodes to ensure other workloads don't run on them.

List nodes in the cluster.

kubectl get no -o wide

NAME    STATUS   ROLES    AGE     VERSION   INTERNAL-IP
qtwtv   Ready    <none>   4h49m   v1.13.0   10.30.0.17  
rxgks   Ready    <none>   4h49m   v1.13.0   10.30.0.16  
uqwst   Ready    <none>   4h49m   v1.13.0   10.30.0.14  
volwl   Ready    <none>   4h49m   v1.13.0   10.30.0.15  
zyisy   Ready    master   4h50m   v1.13.0   10.30.0.13

Let's choose zyisy and rxgks as our reflector nodes.

Download calicoctl on the host.

wget https://github.com/projectcalico/calicoctl/releases/download/v3.4.0/calicoctl-linux-amd64
chmod +x calicoctl-linux-amd64
sudo mv calicoctl-linux-amd64 /usr/local/bin/calicoctl

Export the Node resource of our chosen nodes to the local file system.

calicoctl get node zyisy --export -o yaml > zyisy.yaml
calicoctl get node rxgks --export -o yaml > rxgks.yaml

Edit each node to include a spec.bgp.routeReflectorClusterID: 1.0.0.1 and a metadata.labels.router-reflector: true An updated version of node zyisy is below.

apiVersion: projectcalico.org/v3
kind: Node
metadata:
  name: zyisy
  labels:
    route-reflector: true
spec:
  bgp:
    ipv4Address: 10.30.0.13/22
    ipv4IPIPTunnelAddr: 192.168.0.1
    routeReflectorClusterID: 1.0.0.1

The routeReflectorClusterID represents the BGP router's cluster id, this is not synonymous with a Kubernetes cluster identifier. Determining whether reflectors should share cluster ids may depend on your topology. You should read about reflector peering and the implications of shared / unique cluster ids to make an informed decision.

Replace the existing Node resources with the updated ones.

calicoctl replace -f zyisy.yaml
Successfully replaced 1 'Node' resource(s)

calicoctl replace -f rxgks.yaml
Successfully replaced 1 'Node' resource(s)

Configure BGP Peering

The BGPPeer resource defines what nodes peer. This is also commonly used when peering Calico's network with your data center fabric by configuring peering to Top of Rack (ToR) routers.

We can make use of the added label route-reflector: true to easily setup a dynamic detection of reflector nodes should peer with.

Add the following node peering connection to ensure calico/node instance peer with the reflector instances.

kind: BGPPeer
apiVersion: projectcalico.org/v3
metadata:
  name: node-peer-to-rr
spec:
  nodeSelector: !has(route-reflector)
  peerSelector: has(route-reflector)

Add peering between the RouteReflectors themselves.

kind: BGPPeer
apiVersion: projectcalico.org/v3
metadata:
  name: rr-to-rr-peer
spec:
  nodeSelector: has(route-reflector)
  peerSelector: has(route-reflector)

Disable node-to-node Mesh

Lastly, we must turn off node-to-node mesh ensuring nodes are only peering with the reflectors they're configured to. This requires altering or adding a default BGPConfiguration.

Check for an existing config, if one exists, modify/replace the existing, otherwise follow steps to create a new one.

calicoctl get bgpconfig default

Create a BGPConfiguration with nodeToNodeMeshEnabled: false and an Autonomous System number (asNumber) of 63400.

apiVersion: projectcalico.org/v3
kind: BGPConfiguration
metadata:
  name: default
spec:
  logSeverityScreen: Info
  nodeToNodeMeshEnabled: false
  asNumber: 63400

Your asNumber may vary based on other BGP configurations throughout your data center(s).

On a non-reflector node, re-run node status.

sudo calicoctl node status

Calico process is running.

IPv4 BGP status
+--------------+-----------+-------+----------+-------------+
| PEER ADDRESS | PEER TYPE | STATE |  SINCE   |    INFO     |
+--------------+-----------+-------+----------+-------------+
| 10.30.0.13   | global    | up    | 03:52:51 | Established |
| 10.30.0.16   | global    | up    | 03:54:11 | Established |
+--------------+-----------+-------+----------+-------------+

IPv6 BGP status
No IPv6 peers found.

We can now see zyisy: 10.30.0.13 and rxgks: 10.30.0.16 are the reflectors this node is peering with! From here, validate network connectivity between pods.

Additional Thoughts and Considerations

I hope you found this post helpful in understanding the configuration of route reflectors with Calico! Below are some additional thoughts and considerations to leave you with.

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