yurthub/

README

YurtHub

YurtHub is a node daemon that supports node autonomy in each edge node. It caches the states of necessary APIServer objects in the local storage when cluster-edge networking is established. In case an edge node is offline, YurtHub guarantees that all the registered components in the node can access the cached APIServer object states, pretending the APIServer is still alive.

Architecture

Here are a few key components in YurtHub:

• Http Server: proxying all the http requests sent to the local listeners to the corresponding handler based on the network connectivity with the cloud site APIServer.
• Load Balancer: sending the requests to one of the cloud site APIServer endpoints. It supports round-robin or priority based routing.
• Cache Manager: providing interfaces to manage the data saved in the local storage. The data are updated based on the https response from the cloud site APIServer, and are read by the Local Proxy in case node is offline.
• Certificate Manager: managing the client certificate for all the components that may access the cloud site APIServer. For example, YurtHub may use the certificate generated by Kubelet to communicate with the cloud site APIServer.
• Health Check: periodically checking the network connectivity between the cloud site APIServer and the node.

Deployment

YurtHub is deployed as a Kubelet static Pod (yaml). We recommend to use yurtctl to install or update Yurthub. See the tutorial.

Data Storage

The cached data are saved in the following node disk location

/etc/kubernetes/cache/{component}/{resource}/{namespace}/{name}.json

• component: obtained from the header of the http request. The key is "User-Agent".
• resource: the type of the cached APIServer object such as pods, configmaps, services and so on.
• namespace: the namespace of the cached APIServer object, optional. Cluster scoped objects do not have namespace.
• name: the name of the cached APIServer object.

Register Customize Components

To leverage the autonomy capability of Yurthub for customize node components that need to access cloud site APIserver, please do the following:

1. Use the Yurthub listener address. For example, localhost:10261.
2. Add Edge-Cache: true to the http request header.
3. Add User-Agent: {component-name} to the http request header. Please avoid using the built-in agent names such as kubelet/flannel/coredns/kube-proxy.
4. Add Accept: application/json or Accept: application/vnd.kubernetes.protobuf to the http request header based on the required serialization format.

Trouble Shooting

1. When you want to test the autonomy function of edge node by rebooting the edge node. The yurthub may not initiate properly. (NOTE: this issue has been fixed by PR #49)