In the network model of Kubernetes and many CNI plugins such as calico, it looks like that there is an assumption that each node has one and only one external network interface used to connect with outer. For Kubernetes, it does not listen to all interfaces. It picks the interface from route table with the default gateway and listens to that. And for calico, When calico/node is started, it determines the IP and subnet configuration following some stragies, after all, it uses only one network interface. Check the route table on the calico node to make sure that.

However, there are some scenarios that a node has multiple external interfaces, all of them are expected to be used to connect with outer. It is very common in the data center. Of course, we can bond them all into bond0 and calico works well over it, there are no barriers for startups since that everything are newly built, the applications, the network, the firewall, the monitor systems, etc. On the other hand, for the company that are tens of years old, applications are designed to run on an isolate LAN. The IT infrastructures are designed to isolate applications by LAN, it does not work well.

In distributed system, there is a best practise that at network level, management panel should be separated from data panel to avoid that some applications run out of network bandwith, and the package of heart beat may be blocked by a long time, and it may run into a chaos.

When the era of Kubernetes and container comes, the lack of network plugin with multiple LANs/interfaces support blocks them from running legacy applications on Kubernetes.

Anchor is a Layer-2 CNI plugin based MacVLAN with multiple LANs/interfaces support. A new born container is attached to a special network interface, based on the LAN which it desires to be in. And via that interface, the container can connect with gateway, it is little different from adding a node to a given LAN, there is no NAT, no tunnel.

For that purpose, it is straightful that the plugin should work at Layer-2 of network model. Newtork virtualization technique such as Bridge and MacVLAN can help us attaching the container to network interface. We prefer MacVLAN over Bridge for its perfermance.

By using MacVLAN network driver, It can assign a MAC address to each container’s virtual network interface, making it appear to be a physical network interface directly connected to the physical network/gateway.

See the picture below which shows the network topology of a kubernetes cluster with Anchor as its CNI plugin.

Project anchor mainly contains four components, They are:

• Anchor is an IPAM plugin following the CNI SPEC.

• Octopus is a main plugin that extends macvlan to support multiple network interfaces on the node. It is useful when there are multiple VLANs in the cluster.

• Monkey is a WebUI that displays and operates the data used by anchor IPAM.

• The backstage hero is the installation script of the anchor, which configures and maintains the network interfaces of the node.

CNI(Container Network Interface), a CNCF project, consists of a specification and libraries for writing plugins to configure network interfaces in Linux containers, along with a number of supported plugins. CNI concerns itself only with network connectivity of containers and removing allocated resources when the container is deleted. Because of this focus, CNI has a wide range of support and the specification is simple to implement.

It is worth mentioning that kubernetes is just one of CNI runtimes, others including mesos, rkt, openshift, etc.

The work flow of anchor running inside a kubernetes cluster shown as the picture below.

MacVLAN is a Linux network driver that exposes underlay or host interfaces directly to VMs or Containers running in the host.

MacVLAN allows a single physical interface to have multiple MACs and ip addresses using MacVLAN sub-interfaces. MacVLAN interface is typically used for virtualization applications and each MacVLAN interface is connected to a Container or VM. Each container or VM can directly get DHCP address or IPAM address as the host would do. This would help customers who want Containers to be part of their traditional network with the IP addressing scheme that they already have.

When using MacVLAN, the containers is NOT reachable to the underlying host interfaces as the packages are intentionally filtered by Linux for additional isolation. This does not meet the SPEC of CNI and causes service in k8s cannot work correnctly. To work around it, we create a new MacVLAN interface named acr1 as shown by the topology, the interface steals the IP and network traffic from the host interface by changing the route table in the host. This work is designed to be done by installation script.

Please knowing that, most cloud providers(Amazon, Google, Aliyun) don't allow promiscuous mode, you may deploy Anchor on your own premises.

Recently, I have no resources(No time, no machines) to test whether anchor works well with other runtimes except kubernetes. The document below focuses on kubernetes.

Prepare the cluster

• Enable promiscuous mode on switch(or virtual switch)
• Create a new kubernetes cluster without any CNI plugin
• Reserve several IPs available for applications

Install Anchor

curl -O https://raw.githubusercontent.com/hainesc/anchor/master/deployment/anchor.yaml

Edit the anchor.yaml using your favorite editor, L means Line below.

• Remove L200 and lines below if the k8s cluster has not enabled RBAC.
• L8, input the etcd endpoints used as the store by anchor, see example at the end of the line.
• L10 - L12, input the access tokens of the etcd, remove if SSL not enabled.
• L18, input the choice whether or not create macvlan interface during the installation.
• L22, input the cluster network information. Use semicolon(;) to seperate between items. eg, item node01,eth0.2,10.0.2.8,10.0.2.1,24 tells install script creating a MacVLAN interface with the master eth0.2 at the node whose hostname is node01, the additional info including IP of the master(eth0.2 here), the gateway and mask of the subnet(10.0.2.1 and 24). You CAN have Multiple items for each node.

Save the change and run:

kubectl apply -f anchor.yaml

Wait for installation to complete, it will create a daemonset named anchor, a service account named anchor, a cluster role and a cluster role binding if RBAC enabled.

There are several works done by the pod which created by the daemonset on each node:

• Copy binary files named anchor and octopus to the node
• Config and write a CNI config file named 10-anchor.conf to the node
• Create MacVLAN interface(s) on the node, the interfaces created here will be removed on node restart, but when the node rejoin the k8s cluster, the daemonset recreates a pod and it will recrete the interfaces.

Preparation

Before the example, we should initialize the etcd store used by anchor.

There are three k-v stores used by the anchor ipam, they are:

At the beginning, the stores are empty, so just input some data following the environment.

Make sure export ETCDCTL_API=3 before run etcd cli, since Anchor uses etcd v3.

I have created a WebUI named Powder monkey to display and operate the k-v stores. The frontend is written in Angular and the backend written in Golang. It is not beautiful since I am newbie to Angular but it works well.

Run example

curl -O https://raw.githubusercontent.com/hainesc/anchor/master/examples/anchor-2048.yaml

Edit L14 and choose a subnet for it, then Run:

kubectl apply -f anchor-2048.yaml

Wait for the installation to complete, it will create a deployment named anchor-2048 and a service named anchor-2048.

kubectl get pods -n default -o wide

will displays the IP binding with the Pod. Open you browser and enjoy the game via the IP of the pod.

Please describe the Pod if some errors, and refer to the log of kubelet for more details.

Anchor uses annotations written in the yaml for passing customized config as you see in the example.

The cni.anchor.org/subnet is mandatory since anchor cannot guess an IP if it don't know which VLAN the pod in.

Please let me know by posting a pull request with the logo of your company if you are using Anchor.

• IPv6 support
• K-V store redesign
• Powder monkey improvement

If you find anchor is useful and helpful, please consider making a donation.

• Bitcoin: 1HainescwMrDfay9cU1yWC6vc8ThZj8uAQ
• Alipay: [email protected]