access k8s apis from outside

4/3/2018

I want to access k8s api resources. my cluster is 1node cluster. kube-api server is listening on 8080 and 6443 port. curl localhost:8080/api/v1 inside node is working. if i hit :8080, its not working because some other service (eureka) is running on this port. this leaves me option to access :6443 . in order to do make api accessible, there are 2 ways.

1- create service for kube-api with some specific port which will target 6443. For that ca.crt , key , token etc are required. How to create and configure such things so that i will be able to access api.

2- make change in waeve (weave is available as service in k8s setup) so that my server can access k8s apis.

anyone of option is fine with me. any help will be appreciated .

-- anujkum
kubectl
kubernetes

1 Answer

4/5/2018

my cluster is 1node cluster

One of those words does not mean what you think it does. If you haven't already encountered it, you will eventually discover that the memory and CPU pressure of attempting to run all the components of a kubernetes cluster on a single Node will cause memory exhaustion, and then lots of things won't work right with some pretty horrible error messages.

I can deeply appreciate wanting to start simple, but you will be much happier with a 3 machine cluster than trying to squeeze everything into a single machine. Not to mention the fact that only having a single machine won't surface any networking misconfigurations, which can be a separate frustration when you think everything is working correctly and only then go to scale your cluster up to more Nodes.

some other service (eureka) is running on this port.

Well, at the very real risk of stating the obvious: why not move one of those two services to listen on a separate port from one another? Many cluster provisioning tools (I love kubespray) have a configuration option that allows one to very easily adjust the insecure port used by the apiserver to be a port of your choosing. It can even be a privileged port (that is: less than 1024) because docker runs as root and thus can --publish a port using any number it likes.

If having the :8080 is so important to both pieces of software that it would be prohibitively costly to relocate the port, then consider binding the "eureka" software to the machine's IP and bind the kubernetes apiserver's insecure port to 127.0.0.1 (which is certainly the intent, anyway). If "eureka" is also running in docker, you can change its --publish to include an IP address on the "left hand side" to very cheaply do what I said: --publish ${the_ip}:8080:8080 (or whatever). If it is not using docker, there is still a pretty good chance that the software will accept a "bind address" or "bind host" through which you can enter the ip address, versus "0.0.0.0".

1- create service for kube-api with some specific port which will target 6443. For that ca.crt , key , token etc are required. How to create and configure such things so that i will be able to access api.

Every Pod running in your cluster has the option of declaring a serviceAccountName, which by default is default, and the effect of having a serviceAccountName is that every container in the Pod has access to those components you mentioned: the CA certificate and a JWT credential that enables the Pod to invoke the kubernetes API (which from within the cluster one can always access via: the kubernetes Service IP, the environment variable $KUBERNETES_SERVICE_HOST, or the hostname https://kubernetes -- assuming you are using kube-dns). Those serviceAccount credentials are automatically projected into the container at /var/run/secret/kubernetes.io without requiring that your Pod declare those volumeMounts explicitly.

So, if your concern is that one must have credentials from within the cluster, that concern can go away pretty quickly. If your concern is access from outside the cluster, there are a lot of ways to address that concern which don't directly involve creating all 3 parts of that equation.

-- mdaniel
Source: StackOverflow