Services and ports

Services can be placed in two groups based on the network interface they bind to. Services binding to the localhost interface are only available from within the host. Services binding to the default host interface are available from outside the host and thus are subject to access restrictions.

Services binding to the default Host interface

Port	Service	Access Restrictions
16443	API server	SSL encrypted. Clients need to present a valid password from a Static Password File.
10250	kubelet	Anonymous authentication is disabled. X509 client certificate is required.
10255	kubelet	Read only port for the Kubelet.
25000	cluster-agent	Proper token required to authorise actions.
12379	etcd	SSL encrypted. Client certificates required to connect.
10257	kube-controller	Serve HTTPS with authentication and authorization.
10259	kube-scheduler	Serve HTTPS with authentication and authorization.
19001	dqlite	SSL encrypted. Client certificates required to connect.

Services binding to the localhost interface

Port	Service	Description
10248	kubelet	Localhost healthz endpoint.
10249	kube-proxy	Port for the metrics server to serve on.
10251	kube-schedule	Port on which to serve HTTP insecurely.
10252	kube-controller	Port on which to serve HTTP insecurely.
10256	kube-proxy	Port to bind the health check server.
2380	etcd	Used for peer connections.
1338	containerd	Metrics port

Containerd and etcd

Both these services are exposed through unix sockets.

Service	Socket
containerd	unix:///var/snap/microk8s/common/run/containerd.sock

Authentication and authorization

Upon deployment MicroK8s creates a Certificate Authority, a signed server certificate and a service account key file. These files are stored under /var/snap/microk8s/current/certs/. Kubelet and the API server are aware of the same CA and so the signed server certificate is used by the API server to authenticate with kubelet (--kubelet-client-certificate).

Initially the server certificates will be issued for:

localhost and all the ip addresses avaliable on the machine, typically it’s LAN address
various mDNS addresses, such as kubernetes.default and kubernetes.default.svc.cluster.local

This will only allow Kubectl to access the API server locally, to access it through the internet and a real domain name you must add it to the file /var/snap/microk8s/current/certs/csr.conf.template, for example:

[ alt_names ]
DNS.1 = kubernetes
DNS.2 = kubernetes.default
DNS.3 = kubernetes.default.svc
DNS.4 = kubernetes.default.svc.cluster
DNS.5 = kubernetes.default.svc.cluster.local
DNS.6 = mydomain.com

After changing, the apiserver-kicker will automatically detect the difference, generate new certs and restart the apiserver. Your DNS server settings and kubeconfig file must be updated appropriately.

Clients talking to the secure port of the API server (16443), such as the Kubectl command line utility, have to be aware of the CA (certificate-authority-data in user kubeconfig).

The authentication strategies enabled by default are:

Static Token File with tokens in /var/snap/microk8s/current/credentials/known_tokens.csv
X509 Client Certs with the client CA file set to /var/snap/microk8s/current/certs/ca.crt

Prior to version 1.19, the following strategy is also available:

Static Password File with password tokens and usernames stored in /var/snap/microk8s/current/credentials/basic_auth.csv

Under /var/snap/microk8s/current/credentials/ you can find the client.config kubeconfig file used by microk8s kubectl.

By default all authenticated requests are authorized as the api-server runs with --authorization-mode=AlwaysAllow. Turning on RBAC is done through microk8s enable rbac.

References

Last updated 8 months ago. Help improve this document in the forum.