Improve persistence of IPAM data

[awh]

From @bboreham on October 6, 2016 9:30

Currently weave-daemonset.yaml specifies an emptyDir volume which is deleted when the pod is deleted. Since upgrading weave-kube require deleting the pods, this is unsafe.

Reading http://kubernetes.io/docs/user-guide/volumes/, I don't see an obviously better choice.

Copied from original issue: weaveworks-experiments/weave-kube#27

[awh]

From @Bregor on October 6, 2016 10:5

I think regular hostPath will suit this as well.
Example:

      volumeMounts:
        - mountPath: /weave_data
          name: data
...
  volumes:
    - name: data
      hostPath:
        path: /var/lib/weave-kube

[awh]

From @bboreham on October 6, 2016 10:7

Sure, but is there a hostPath we can guarantee to be able to write to on every Linux distro?

CoreOS, for instance, mounts loads of things read-only.

[awh]

From @Bregor on October 6, 2016 10:9

CoreOS mounts /usr for read-only, but /var and /opt are available to be overwritten.

[awh]

These may be of use:

http://kubernetes.io/docs/user-guide/petset/
http://kubernetes.io/docs/user-guide/persistent-volumes/

[awh]

From @Bregor on October 12, 2016 9:38

Petset without "normal" network fs is bloody hell. Regular hostPath will be much better for this task I mean.

[bboreham]

I changed this from a feature to a bug because we have more reports of trouble after deleting all Weave pods.

Note that we need to give some thought to whether a user would ever need to really clear out the data, after we made it more persistent, and if so how they would do that. I.e. what is the equivalent of weave reset on Kubernetes?