The answer to "how does the user know how to X?" is the same as it always has been. Documentation. Now, that's not to say that we still don't need to do some work to make it intuitive... but I think that for something that is complicated like HA, leaning on documentation a little more is ok.
More inline: On Wed, Nov 6, 2013 at 1:49 PM, roger peppe <rogpe...@gmail.com> wrote: > The current plan is to have a single "juju ensure-ha-state" juju > command. This would create new state server machines if there are less > than the required number (currently 3). > > Taking that as given, I'm wondering what we should do > in the future, when users require more than a single > big On switch for HA. > > How does the user: > > a) know about the HA machines so the costs of HA are not hidden, and that > the implications of particular machine failures are clear? > - As above, documentation about what it means when you see servers in juju status labelled as "Juju State Server" (or whatever). - Have actual feedback from commands: $ juju bootstrap --high-availability Machines 0, 1, and 2 provisioned as juju server nodes. Juju successfully bootstrapped environment Foo in high availability mode. or $ juju bootstrap Machine 0 provisioned as juju server node. Juju successfully bootstrapped environment Foo. $ juju ensure-ha -n 7 Enabling high availability mode with 7 juju servers. Machines 1, 2, 3, 4, 5, and 6 provisioned as additional Juju server nodes. $ juju ensure-ha -n 5 Reducing number of Juju server nodes to 5. Machines 2 and 6 destroyed. b) fix the system when a machine dies? > $ juju destroy-machine 5 Destroyed machine/5. Automatically replacing destroyed Juju server node. Machine/8 created as new Juju server node. > c) scale up the system to x thousand nodes Hopefully 12 machines is plenty of Juju servers for 5000 nodes. We will need to revisit this if it's not, but it seems like it should be plenty. As above, I think a simple -n is fine for both raising and lowering the number of state servers. If we get to the point of needing more than > d) scale down the system? > $ juju disable-ha -y Destroyed machine/1 and machine/2. The Juju server node for environment Foo is machine/0. High availability mode disabled for Juju environment Foo.
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