Feedback from a new charm author

[Dean Maniatis]

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).

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.

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?

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?


Dean


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