Feedback from a new charm author

[Marco Ceppi]

Hey Dean! Thanks for the email. I've got some replies in line.

On Mon, Dec 5, 2016 at 11:22 AM Dean Maniatis <dean.maniatis at gmail.com>
wrote:

Hello,

I'm a new charm author trying to learn the basics and decided to start with
a simple bash template. I'm working on porting netdata
<https://github.com/firehol/netdata> as a subordinate charm which is a
lightweight real-time performance and health monitoring tool. On my first charm
revision <https://github.com/deanmaniatis/netdata-charm> i managed to
deploy it and test it with Xenial and Trusty both on LXD and AWS. I have
identified the following challenges/questions and since i couldn't find any
information from docs i decided to post here. Some maybe more related to
feature requests than actual questions so please treat the following as a
mixed feedback from a newbie.


1. How to test centos7 series? The upstream developer has put a lot of
effort to support all major Linux distributions but i can't seem to be able
to find any information regarding "charming" in regards with Centos7. After
some quick research it seems that currently centos7 image is not supported
in either AWS or localhost provider
<https://bugs.launchpad.net/juju/+bug/1495978>. In addition, it seems there
are no centos7 charms to look into their code nor even a simple blank
centos7 charm to be used as a sandbox (similar to the ubuntu charm).

This is a good point. I'll make sure we update with a "centos"  charm much
like the Ubuntu one! Cloudbase has done a lot of the Centos charm
enablement and charms. I'll have them weigh in with some examples.

2. When i first deployed my subordinate charm i couldn't figure why i was
able to relate it to only to a few charms and not all available on the
canvas. Later i understood that i have to deploy at least one for each
series which somehow doesn't provide this really cool user experience of
application modeling, i.e. deploy a single subordinate charm and during
relation let the system/charm code handle the intricate details and provide
meaningful message in case the relation is not feasible, e.g. this charm is
not supported for this series. There is an informative message when using
CLI but on the GUI it simply grays out the target charm and it is not
really clear why that's not possible.

This bit me, again, recently. I filed this as a bug to get it addressed
soon. https://bugs.launchpad.net/juju/+bug/1638199

3. When a subordinate charm enables a new service on the principal charm
shouldn't that service be listed under the `Expose application` GUI
section? For example my charm enables a web UI dashboard on port 19999 so i
would expect that to be added to whatever other service is listed under the
principal charm. I've define this service on metadata.yaml with `provides:
website: interface: http` and with `open-port 19999` on install hook but
doesn't seem to be working. What am i doing wrong?

Not sure I understand, you should be able to expose the subordinate at
anytime. Since the port and metadata relationships are defined as part of
that charm, `juju expose netdata` should do what you want.

4.I can easily deploy an application bundle with one command but the
opposite is not available except manually removing each service or
destroying completely the model. Shouldn't `juju remove kubernetes-core`
just work?


So, ideally yes. However bundles aren't modelled in juju past the
deployment. Bundles themselves are just a static representation of a
snapshot of a model. As such, when you `juju deploy kubernetes-core` you're
really replaying the applications and relations (and configuration) for
that bundle. To date, juju controller doesn't track that past the deploy. I
think there is work in the future to improve bundles, but I'm not sure if
this is considered as one of them.

Marco
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