Best Practice Question: Multiple non-overlapping groups for one host - best alternative?

[David Fritzsche]

Hi all,

in the setup I would like to automate with ansible I have mostly servers with
distinct purposes and on each server they may be several distinct
services/components. The plan is to use ansible to have the configuration of
all these servers in one place and to enable us to setup staging environments
for the new software we develop and for new releases of the software stack we
use (mariadb, nginx, ...)

Since we want to be able to rearrange the "services" (i.e., a database or a
FastCGI application) independently to different hosts I started to organize
everything into ansible groups, i.e., I have groups like

- database_01
- database_02
- ...
- fcgi_01
- fcgi_02
- ...

for each group I set variables in group_vars/<group-name>, which looks a
little bit like the following:

group_vars/database_01::
---
database_name: db01
database_user: user01
database_password: xxxxx
....

and then I have defined roles so that I can use very simple playbooks to roll
this setup out:

database_01.yml::
---
- hosts: database_01
roles: [ database_role ]


Now for the tricky part: The way ansible works this can not work if I have two
databases on the same host. Then I would have two database groups (e.g.,
database_01 and database_01) that contain the same host

hosts::
[database_01]
db_host

[database_02]
db_host

and the playbook would load for host db_host the variables of all groups that
include db_host, i.e, the variables of both database_01 and database_02 are
loaded and I do not install the correct database when running the playbook.


Is there some best practice how to configure small "components" (databases,
fastcgi applications, ...) so that I can separate the configuration of the
component from the configuration where the component is going to be installed
and I can have multiple "components" of the same kind on the same host?

[James Cammarata]

Hi David, the best way to do this would be to make the role aware of the fact that there may be more than one database installed on it, so that the variables in the group would then become an array:

# group_vars/foo.yml:

databases:

- name: db01

  user: db_user1

  password: xxxxxx

- name: db02

  user: db_user2

  password: xxxxxx

  ...

And then you would loop over this list in your role tasks.

Hope that helps!

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[David Fritzsche]

Hi James,

thanks for the tip. I think the approach is not totally suitable for my
situation. I would rather not define all the databases for one server in one
place for two reasons:

I would like to have it very easy to "move" the database to a different server
(only in the sense that it gets installed on a different server if I run
everything from scratch to install a test/staging environment)

Also quite important is that I want to be able to run a playbook that installs
just db01 and not db02 to save development time (e.g., when I change the
database schema of db01, but do not want to run the tasks that check if there
needs to be updates to db02 or when I want to setup a new test environment
where I know that I do not need db02...).

Maybe there is a way to setup things that I have to compromise at most on one
of these things?

On 20.11.2014 17:18, James Cammarata wrote:
> Hi David, the best way to do this would be to make the role aware of the fact
> that there may be more than one database installed on it, so that the
> variables in the group would then become an array:
>
> # group_vars/foo.yml:
> databases:
> - name: db01
> user: db_user1
> password: xxxxxx
> - name: db02
> user: db_user2
> password: xxxxxx
> ...
>
> And then you would loop over this list in your role tasks.
>
> Hope that helps!
>
>
> On Thu, Nov 20, 2014 at 5:30 AM, David Fritzsche
> <david.fritzsche...@mvua.de

> <mailto:ansible-project%2Bunsu...@googlegroups.com>.

> To post to this group, send email to ansible...@googlegroups.com

> <mailto:ansible...@googlegroups.com>.

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> For more options, visit https://groups.google.com/d/optout.
>
>

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[Brian Coca]

define all DBs in group_vars/all

then have 3 groups:

[singledbA]

mydbs = dbA

[singledbB]

mydbs = dbA, dbB

[bothddbs]

mydbs = dbA,dbB

then have the task that installs them use use the  mydbs

you can even define mydbs by host

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Brian Coca