Newbie Question: How do I replace a machine in a deployed Model?

[Rick Harding]

On Thu, Aug 31, 2017 at 11:07 AM Raghurama Bhat <rbhat at proofpoint.com>
wrote:

> Hi,
>
>
>
> I have a newbie question. I deployed a two node Kubernetes Core Cluster
> using Juju  into a MaaS Setup.   Now if I one of the Machine has a hardware
> failure, What is the process for replacing it with another machine? Does
> Juju controller monitor the cluster and request MaaS for a new machine if
> it detects one of the machines is gone? Even if this has to be done
> manually, I did not see a replace-machine option to Juju. Only add and
> remove units and machines. How does this work?
>

 Juju does not automatically do anything here. The best thing is to have
proper monitoring on your machines and in case of a failure such as this
you can update things in a number of ways. If you want to replace exactly
what's on the failed machine in this case it depends on if it was the first
or second machine the bundle uses.

If it was the second one, it looks like that's only the kubernetes-worker
node and so you can create a new one with:

    juju add-unit kubernetes-worker

The constraints from the bundle should still be in place, the config will
be the same, etc.

If it's the first machine that went down. That's trickier because it has
some colocated applications on it. So you'd want to add-unit to something
that gets a newly allocated machine:

    juju add-unit kubernetes-master

And then put back the other services using placement directives [1]

    juju add-unit etcd --to=3 # this assumes that the newly created machine
for the kubernetes-master is #3
    juju add-unit easyrsa --to lxd:3

One thing to note is that since you're using the non-HA production bundle
that there's no fail over of the actual data running in the applications.
Your Kubernetes master will get any charm config that's been set before,
but it won't have any work you did directly against the Kubernetes cluster.

Typically, we'd suggest that you have things in an HA setup and with
monitoring such that you could then detect a failure, and respond to that
how you wish. You might add-units into containers on existing machines, you
might allocate new machines, or some other response to the failure.

Rick


1:
https://jujucharms.com/docs/2.2/charms-deploying#deploying-to-specific-machines-and-containers
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