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I was wondering if someone could give me a brief overview of the differences/ advantages between all of the different Kubernetes network overlays. The getting started guide (http://kubernetes.io/docs/getting-started-guides/scratch/#network) mentions the following:
But doesn't really explain what the differences between them are or what the advantages and disadvantages each one has. I was wondering if someone could give me an idea of which one of these solutions I should be using for a bare metal CentOS 7 cluster.
Thanks!
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Thus Flannel is a great entry level choice for Kubernetes cluster networking, however, if you are looking for advance networking features, you may want to consider other CNI options such as Calico.
Many Kubernetes network implementations use overlay networks. Typically for these deployments, when a pod initiates a connection to an IP address outside of the cluster, the node hosting the pod will use SNAT (Source Network Address Translation) to map the source address of the packet from the pod IP to the node IP.
You often hear about overlay networks in the context of Kubernetes networking. While this may sound complicated, an overlay network simply involves another layer of encapsulation for network traffic. For example, the Flannel network plugin takes traffic from a pod and encapsulates it inside the VXLAN protocol.
Flannel is an overlay network mechanism where as Calico is basically a pure L3 play. Flannel works by using a vxlan device in conjunction with a software switch like linux bridge or ovs. Container A when tries to reach container B on different host the traffic is pushed to the bridge on host A via the VETH pair.
This comparison matrix was shared several times on Kubernetes' Slack and may be useful.
However, beware potentially out-of-date information, keep in mind the "devil is in the details" so the reality may not be as simple as it would seem according to this document. All available solutions will have pros and cons, but will also be more suitable for some use-cases than others, so as always, it is a question of trade-offs and YMMV.
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