Accumulating a list in Ansible

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1

Hello, group. I am still a novice with Ansible, so perhaps my approach is flawed, so if there is a better way, I am happy to hear about it. I have a situation where I need to accumulate values into an Ansible list variable on a role-by-role basis, and then use the contents of that list in another role in order to populate a config file template. So, suppose I have these roles:

  • roles:
  • service1
  • service2
  • service3
  • make-config-file

And a variable ‘services’. I would like to end up with services having a value of [ service1, service2, service3 ] by the time ‘make-config-file’ is executed so that it can write those values out to the config file.

So, the question is, how do I push a value onto the ‘services’ list in each role? I understand how to get the values from the list into the config file, I am just not sure how to accumulate a list in Ansible.

Thanks,
Kevin

2

you can use union filter:

services: "{{service1|union(service2)|union(service3)}}"

3

Brian, thanks for the tip.

Is there any way to do the moral equivalent of "list_behaviour=append"?
In other words, to be able to append items to an already-declared list?

I originally wanted this so that roles could declare all the packages
they needed, and they could be installed in one go by a common task.
There are many other (better) reasons, e.g. modifying my PostgreSQL
configuration if I'm also installing the postgres_replication role.

Would anyone else find this useful?

-- Abhijit

P.S. I'm open to suggestions for some way to do this using a local
plugin of some sort. I just want to get it to work somehow.