Merge pull request #4474 from justinsb/etcd_manager_roadmap

Add (proposed) roadmap for etcd

docs/etcd/roadmap.md

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+# Kops and etcd
+
+Kops currently manages etcd using a daemon that runs on the masters called protokube.  protokube
+is responsible for:
+
+* mapping volumes so that exactly one master runs each member of the etcd cluster,
+even when the masters are dynamic (in autoscaling groups).
+* mapping DNS names so that etcd nodes can discover each other even as they move around.
+
+We are following the [approach recommended by the authors of etcd](https://github.com/coreos/etcd/issues/5418)
+
+protokube has additional responsibilities also, so we call this the protokube-integrated etcd support.
+
+Generally, splitting up protokube is part of the general kops roadmap, where we aim to split out our integrated
+tooling into composable tooling that can be upgraded (or even used) separately.
+
+## Limitations
+
+The current approach for managing etcd makes certain tasks hard:
+* upgrades/downgrades between etcd versions
+* resizing the cluster
+
+To address these limitations, we plan to adopt the [etcd-manager](https://github.com/kopeio/etcd-manager) as
+it matures.
+
+To make adoption easier, the etcd-manager has added a standalone backup tool, that can backup etcd into the
+[expected structure](https://github.com/kopeio/etcd-manager/blob/master/docs/backupstructure.md), even if you are not running the etcd-manager.  It should be possible to then use
+the etcd manager from that backup.
+
+## Roadmap
+
+### _kops 1.9_
+
+* Use the etcd-backup tool to allow users to opt-in to backups with the protokube-integrated etcd support, in the format that etcd-manager expects
+
+Goal: Users can enable backups on a running cluster.
+
+### _kops 1.10_
+
+* Make the etcd-backup tool enabled-by-default, so everyone should have backups.
+* Allow users to opt-in to the full etcd-manager.
+* Make etcd3 the default for new clusters, now that we have an upgrade path.
+
+Goal: Users that want to move from etcd2 to etcd3 can enable backups
+on an existing cluster (running kops 1.9 or later), then enable the etcd-manager (with kops 1.10 or later).
+
+### _kops 1.11_
+
+* Make the etcd-manager the default, deprecate the protokube-integrated approach
+
+Goal: Users are fully able to manage etcd - moving between versions or resizing their clusters.
+
+### _untargeted_
+
+* Remove the protokube-integrated etcd support (_untargeted_)