[Review Queue] mysql 15-configs test

[Matt Bruzek]

I spent some time in the Review Queue taking a look at the mysql tests that
were added by nicopace.

https://code.launchpad.net/~nicopace/charms/trusty/mysql/multiple-configs-one-instance

I am happy to have more tests to exercise mysql, but I found the test was
not deploying the correct series of the charm.

The tests did not run from my computer and I found several problems that I
proposed solutions to in a merge proposal to the original proposal.

https://code.launchpad.net/~mbruzek/charms/trusty/mysql/fix-tests

Thanks,

   - Matt Bruzek 
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Re: adding placement directives for ensure-availability

[Nate Finch]

Briefly, the problem with ensure-availability is that it does too much.  It
converts a non-HA environment into an HA environment.  If you're already in
HA and you specify a larger number of servers, it'll add servers.  If some
servers are down, it'll start new ones and remove the down ones.

There are plans to split the command into multiple commands, so that it's a
little easier to understand what it'll do in any particular case.  However,
that work is much bigger than what we are proposing here.

This proposal simply fixes a use case that is tripping up the Landscape
team, which is that they want to make their deployment more dense... with
the option to replace a downed state server with a container on an existing
machine in the environment.

On Tue, Feb 24, 2015 at 12:40 PM, Gustavo Niemeyer <
gustavo.nieme...@canonical.com> wrote:

> Hi Nate,
>
> On Tue, Feb 24, 2015 at 2:24 PM, Nate Finch 
> wrote:
> (...)
> > To support this, we need a way to say "use the default placement policy".
> > For this, we propose the keyword "default".  Thus, to fix the above
> example,
> > Bill would type this:
> >
> >> $ juju ensure-availability --to lxc:1,default
> >> 
>
> What's the full format of the parameter of --to, with all possible details?
>
> > Note that this change in no way fixes all of HA's UX problems, and that
> it
> > actually makes some of the problems a lot more obvious (such as the fact
> > that the number of placements you need can be different even for the same
> > command, depending on the state of the environment).  This will be fixed
> > when we revamp the CLI, but for now we'll have to live with it.
>
> I don't have much context on the problem, but it seems like the
> proposal is a change in the design of the CLI. If there are known
> problems on the current design, the change might well fix it instead
> of making it worse?
>
>
> gustavo @ http://niemeyer.net
>
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Re: adding placement directives for ensure-availability

[Gustavo Niemeyer]

Hi Nate,

On Tue, Feb 24, 2015 at 2:24 PM, Nate Finch  wrote:
(...)
> To support this, we need a way to say "use the default placement policy".
> For this, we propose the keyword "default".  Thus, to fix the above example,
> Bill would type this:
>
>> $ juju ensure-availability --to lxc:1,default
>> 

What's the full format of the parameter of --to, with all possible details?

> Note that this change in no way fixes all of HA's UX problems, and that it
> actually makes some of the problems a lot more obvious (such as the fact
> that the number of placements you need can be different even for the same
> command, depending on the state of the environment).  This will be fixed
> when we revamp the CLI, but for now we'll have to live with it.

I don't have much context on the problem, but it seems like the
proposal is a change in the design of the CLI. If there are known
problems on the current design, the change might well fix it instead
of making it worse?


gustavo @ http://niemeyer.net

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adding placement directives for ensure-availability

[Nate Finch]

Please note that this email is about a feature that needs to be
significantly finished by Friday, so if you think you might want to
comment, please do so ASAP.

There is currently a requirement

to let ensure-availability create state servers in containers on existing
machines in a juju environment.  The way this would work is just like the
standard placement directives, i.e. you'd use something like lxc:1 to put a
state server in a new container on machine 1.

There are a couple changes I'd like to propose to the requirements listed
(I'd add them in the doc itself, but it's read-only for me Ian or
whoever wrote it, could you make it writeable or at least comment-able?)

Ensure-availability may create multiple machines, so we need to support
multiple placement directives.  Currently, the requirements doc says that
if you have fewer placements than machines that need to be created, any
remaining machines will be created using the default policy of grabbing a
new machine from the provider.  However, in talking with John, we don't
think this is good behavior.

We would prefer that the placement be explicit, so that if you need 4 new
machines, you have to explicitly say where to place all of them. This way,
if you make a mistake and don't specify enough placements, we can give you
an error.  We think this is preferable, because where your state machines
live is quite important, and very difficult to change, so helping a user
avoid mistakes is quite valuable.

Example:  Bill has one state machine, and wants to go to HA with 3
machines.  He runs the following command:

$ juju ensure-availability --to lxc:1
> Error: Two state servers need to be added, but only one placement
> specified.


To support this, we need a way to say "use the default placement policy".
For this, we propose the keyword "default".  Thus, to fix the above
example, Bill would type this:

$ juju ensure-availability --to lxc:1,default
> 


Note that this change in no way fixes all of HA's UX problems, and that it
actually makes some of the problems a lot more obvious (such as the fact
that the number of placements you need can be different even for the same
command, depending on the state of the environment).  This will be fixed
when we revamp the CLI, but for now we'll have to live with it.

-Nate
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