Oh hold on. the *service cluster IP range* is not for pod IPs at all. It's
for the ClusterIP of services, so you can have up to 64k services in a
cluster at the default setting. The range for pods is the --cluster-cidr
flag on kube-controller-manager.


On Fri, Aug 11, 2017 at 3:05 PM David Rosenstrauch <dar...@darose.net>
wrote:

> Actually, that begs another question.  The docs also specify that k8s
> can support up to 5000 nodes.  But I'm not clear on how the networking
> can support that.
>
> So let's go back to that service-cluster-ip-range with the /16 CIDR.
> That only supports a maximum of 256 nodes.
>
> Now the maximum size for the service-cluster-ip-range appears to be /12
> - e.g., --service-cluster-ip-range=10.240.0.0/12  (Beyond that you get a
> "Specified service-cluster-ip-range is too large" error.)  So that means
> 12 bits for the high part of the address, and with each node taking the
> lower 8 bits for the IP address of individual pods, that leaves 12
> remaining bits worth of unique IP address ranges.  12 bits = 4095
> possible IP addresses for nodes.  How then could anyone scale up to 5000
> nodes?
>
> DR
>
> On 2017-08-11 10:47 am, David Rosenstrauch wrote:
> > Ah.  That makes a bit more sense.
> >
> > Thanks!
> >
> > DR
> >
> > On 2017-08-11 10:41 am, Ben Kochie wrote:
> >> Kuberentes will be giving a /24 to each node, not each pod.  Each node
> >> will give one IP out of that /24 to a pod it controls.  This default
> >> means you can have 253 pods-per-node.  This of course can be adjust
> >> depending on the size of your pods and nodes.
> >>
> >> This means that you can fully utilize the /16 for pods (minus per-node
> >> network, broadcast, gateway)
> >>
> >> On Fri, Aug 11, 2017 at 4:36 PM, David Rosenstrauch
> >> <dar...@darose.net> wrote:
> >>
> >>> According to the docs, k8s can support systems of up to 150000 pods.
> >>> (See https://kubernetes.io/docs/admin/cluster-large/ [1])  But
> >>> given k8s' networking model, I'm a bit puzzled on how that would
> >>> work.
> >>>
> >>> It seems like a typical setup is to assign a
> >>> service-cluster-ip-range with a /16 CIDR.  (Say 10.254.0.0/16 [2])
> >>> However, I notice that my cluster assigns a full /24 IP range to
> >>> each pod that it creates.  (E.g., pod1 gets 10.254.1.*, pod2 gets
> >>> 10.254.2.*, etc.)  Given this networking setup, it would seem that
> >>> Kubernetes would only be capable of launching a maximum of 256 pods.
> >>>
> >>> Am I misunderstanding how k8s works in this r?  Or is it that the
> >>> networking would need to be configured differently to support more
> >>> than 256 pods?
> >>>
> >>> Thanks,
> >>>
> >>> DR
> >>>
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