How to detect which role called an other role in case of role dependency

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1

Hi,

I have a playbook with many roles plus a common role that is used by each other roles.
Basically, this common role is used because I have some tasks that are applicable for all roles, obviously, I don’t want to rewrite these tasks as many time as I have a role.
Recently I encountered a case where I need a task to be played for all roles except only one. Therefore, I’m looking for a way to detect which role issued the call to the common role due to dependency so I could filter when to skip the task or not with a simple when statement.

`

├── roles
│ ├── common
│ │ ├── defaults
│ │ │ └── main.yml
│ │ └── tasks
│ │ ├── main.yml
│ │ └── test.yml
│ ├── first_role
│ │ ├── meta
│ │ │ └── main.yml
│ │ └── tasks
│ │ └── main.yml
│ └── second_role
│ ├── meta
│ │ └── main.yml
│ └── tasks
│ └── main.yml
└── site.yml
`

The only way I see at the moment to achieve that would be something like following:

`

./hosts[group1]

laptop ansible_host=127.0.0.1
`

`

./site.yml

2

This sounds like you're re-discovering why OOP is such a pain in the arse.

Sorry to be glib but I see this a lot and it's usually easier for everyone if
you just avoid the whole meta dependency thing altogether, it's always
a maintenance
hassle. If you get this to work it's just another maintenance headache
for you or
the next guy who maintains this playbook.

3

This.

I always used to suggest to people – strongly – that they avoid using meta to pull in other roles, because it’s frankly unkind to your colleagues.

Role dependency paths are sooo much easier to visualise if you just list them in the order you need them in a parent play. Simples!

4

Hi,

I have a playbook with many roles plus a common role that is used by
each other roles.
Basically, this common role is used because I have some tasks that
are applicable for all roles, obviously, I don't want to rewrite
these tasks as many time as I have a role.
Recently I encountered a case where I need a task to be played for
all roles except only one. Therefore, I'm looking for a way to detect
which role issued the call to the common role due to dependency so I
could filter when to skip the task or not with a simple `when`
statement.

For start, I would suggest looking at this not from perspective of what
role depends on the common role, but instead what task in the common
role needs to be optional. The optional tasks performed could be viewed
as optional "features" of a role.

I.e. when you pass in the parameter to the "common" role, it should be
more along the lines of "enable_BLAH", "operation_mode" or something
similar. You want to put emphasis on what it is that will get run or
not.

1/ The fact that I need to hardcode the rolename is not something
really clean I think.

As mentioned above, use a more logical name for the parameter. In this
specific case you probably want to have a boolean (True/False) value for
it.

2/ I'm obliged to declare a default variable for `parent_role` to
avoid an error message :

"The error was: 'parent_role' is undefined"

Indeed, when my common role is played and was not called by my role
that doesn't need to exclude the task from being played, I'll get
this error since I do not pass the `parent_role` variable from the
other roles.

Declaring defaults for roles is a perfectly ok thing to do - just keep
in mind what I wrote above apropos naming the parameter and its syntax.

As a side-note, there are some other ways to handle defaults for
undefined variables, like (although, I would say it is better to
declare values in defaults/main.yml instead):

http://docs.ansible.com/ansible/playbooks_filters.html#defaulting-undefined-variables

There is also the "when: foo is defined" syntax (which can be combined
with logical and/or as well). But you probably don't need it for your
use-case :slight_smile:

Maybe someone know a nicer way to do this ?

For an alternative to meta dependencies (although I have not tried this
myself, so take it with a grain of salt), have a look at:

http://docs.ansible.com/ansible/include_role_module.html

I would find the include_role module more useful in cases where you
want to control ordering in more complex way than just the "meta deps
first" -> "then this role".

Finally, you had two replies related to avoid dependencies via meta,
something you should consider as well (I thought it'd be nice to
provide at least one more way to handle things :slight_smile:

Best regards