resolve dependency between services

[Sebastian]

Tudor, see the bash branch:
https://github.com/sebas5384/charm-drupal/tree/bash

Abs,
Sebas.



2014-05-21 14:35 GMT-03:00 Sebastian <sebas5384 at gmail.com>:

> Hey Tudor! thanks for doing a new charm! :D
>
> I can show you a charm I'm doing for Drupal, take a look:
> https://github.com/sebas5384/charm-drupal
>
> Drupal needs MySQL to work, so you can do:
> - Only enable ports like 80 when the db-relation-changed hook is fired,
> and the relation to mysql must be required in the metadata.yaml
> - You can do a bundle to ensure the topology, like openstack for example.
>
> I'm planning to do the two :)
>
> Cheers,
> Sebas.
>
>
>
> 2014-05-21 11:53 GMT-03:00 Tudor Rogoz <rogoz at adobe.com>:
>
>>   Hi,
>>
>>
>>  I'm new to juju and I just started to work on a new charm and I'm not
>> sure how to solve several issues.I will appreciate any advice on this.
>>
>>
>>  The topology that I want to achieve is described bellow:
>>
>>
>>  My service (i will call it application service) "strongly" depends on
>> the mongodb service [0].This means that the application service cannot be
>> installed and started without a mongo previously configured for storing the
>> application data.The problem is that when I'm deploying the service,
>> automatically the install, config-service and start hooks will be
>> triggered, but at this point my service cannot know about mongo service
>> because a relation between the 2 services is not established yet.So, it's
>> impossible for me to perform the product installation in the install
>> hook.An ugly workaround would be to perform the installation in the
>> relation-joined/relation-cahnged hook, but this would be my last
>> option.Even in this case the service unit will appear as "started" after
>> the start hook ends, but nothing will actually run there.
>>
>> I would like for the charm to support the following scenario.
>>
>> 1/I deploy the application service
>>
>> 2/ the service unit remains in a pending state before the installation
>> hook will run because the service unit has no access to a mongo service
>>
>> 3/ deploy the mongo service which successfully starts
>>
>> 4/ add a relation between mongo and application service. The app service
>> will get the mongo connection information
>>
>> 5/ application service installation starts (the install hook is
>> unblocked), and successfully starts
>>
>>
>>
>>  Another problem that i have is the following:
>>
>>    For example, one of my application units is getting the connection
>> details from a specific mongodb unit while running the relation hook, were
>> i can store the specific information for using it in another hook? Is there
>> anything implemented in juju for this, or I should write the information in
>> a file and store it on disk and read from there when is need it?
>>
>>
>>  [0] https://github.com/charms/mongodb
>>     <https://github.com/charms/mongodb>
>>   charms/mongodb · GitHub
>>  mongodb - Mirror of juju charm, pull requests and modifications welcome!
>>  Read more... <https://github.com/charms/mongodb>
>>    ​
>>
>>
>>  Thanks a lot,
>>
>> Tudor
>>
>>
>>
>> --
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>>
>>
>
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