This is a text-only version of the following page on https://raymii.org:
---
Title : Ansible: access group vars for groups the current host is not a member of
Author : Remy van Elst
Date : 27-01-2017
URL : https://raymii.org/s/tutorials/Ansible_access_other_groups_group_vars.html
Format : Markdown/HTML
---
![ansible logo][1]
This guide shows you how to access group variables for a group the current host
is not a member of. In Ansible you can access other host variables using
`hostvars['hostname']` but not group variables. The way described here is
workable, but do I consider it a dirty hack. So why did I need this? I have a
setup where ssl is offloaded by haproxy servers, but the virtual hosts and ssl
configuration are defined in Apache servers. The loadbalancers and appservers
are two different hostgroups, the ssl settings are in the appserver group_vars,
which the hosts in the loadbalancer group need to access. The best way to do
this is change the haproxy playbooks and configuration and define the
certificates there, but in this specific case that wasn't a workable solution.
Editing two yaml files (one for the appservers and one for the loadbalancers)
was not an option in this situation.
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This is applicable for other scenario's as well. In templates this can be worked
around by looping over all the groups, then over all the hosts in the specific
group, then if the host is the first in the loop, go over all the hostvars for
that host and then access the group var you want. [This stackoverflow][3] post
goes over that. In my case I needed to access it in a playbook, the looping
construction woudln't work there.
### The inventory
In the inventory file I created a new group. This group has the two other
groups, `appservers` and `loadbalancers` in them and nothing else. Like so:
[appserver]
app1.cluster
app2.cluster
[loadbalancer]
lb1.cluster
lb2.cluster
[ssl:children]
loadbalancer
appserver
The shortnames expand to specifc SSH configuration. The `ssl` hostgroup
effectively includes the following hosts:
* app1
* app2
* lb1
* lb2
However, we do need to modify the playbook that modifies the vhosts to only
place the certificates on the loadbalancers, and do nothing with the
certificates on the appservers. The playbook should still do it's normal thing,
configuring the vhosts, on the appservers, but not on the loadbalancers.
[The documentation][4] has more information on hostgroups based on other groups.
### The playbook
The playbook (`deploy-vhosts.yml`) first was this:
---
- hosts: appserver
roles:
- apache-vhost
After changing the hostgroup we need to add the specific role that deploys the
certificates. We also put a `when` in place to make sure the two roles only run
on the hosts where they should and not the other hosts:
---
- hosts: ssl
roles:
- {role: apache-vhost, when: "'appserver' in group_names" }
- {role: sslcerts, when: "'loadbalancer' in group_names " }
### The group vars
The group vars for the appservers contain the following information to configure
the virtual hosts:
---
apache_vhost:
example.cluster.nl:
name: example.cluster.nl
docroot: /home/example-cluster/domains/example.cluster.nl/public-html/
webuser: example-cluster
ssl_name: example.cluster.nl
serveraliases:
- www.example.cluster.nl
example2.cluster.nl:
name: example2.cluster.nl
docroot: /home/example2-cluster/domains/example2.cluster.nl/public-html/
webuser: example2-cluster
ssl_name: example2.cluster.nl
serveraliases:
- www.example2.cluster.nl
The problem is that, when the deploy vhosts playbook in run on the
loadbalancers, they cannot access these variables since they are not in the same
group.
### The role
The role `sslcerts` has one task file and one handler (`restart haproxy`). It
makes sure the folder for the certificates exists and it places the certificate
files there. There are extra when statements to make sure it only runs on the
loadbalancers.
- name: create ssl folder
file:
path: /etc/ssl/cluster/
state: directory
owner: root
group: root
when: "'loadbalancer' in group_names"
tags: ssl
- name: place certificates
copy:
src: files/ssl/{{ item.value.ssl_name }}.pem
dest: /etc/ssl/cluster/{{ item.value.ssl_name }}.pem
with_dict: '{{ apache_vhost }}'
when: "'loadbalancer' in group_names"
notify: restart haproxy
tags: ssl
### The crux
Even after configuring the special playbook that runs on all the hosts, the
loadbalancers still cannot access the group variables from the appservers. The
dirty hack part is that we symlink the group vars from the `appserver` folder to
the `loadbalancer` folder:
ln -s /home/deploy/ansible/group_vars/appserver/apache-vhost.yml
/home/deploy/ansible/group_vars/loadbalancer/apache-vhost-symlink.yml
Now, the loadbalancers have the group variable `apache_vhost` as well, and when
the file in the `appserver` folder is changed, the `loadbalancer` file is as
well because it's a symlink.
### haproxy
haproxy in this case has one frontend where all traffic comes into, the
appservers handle the different virtual hosts:
frontend https-in
mode http
bind 1.2.3.4:443 ssl crt /etc/ssl/cluster/ no-sslv3
acl secure dst_port eq 443
rsprep ^Set-Cookie:\ (.*) Set-Cookie:\ \1;\ Secure if secure
rspadd Strict-Transport-Security:\ max-age=31536000 if secure
option httplog
option forwardfor
option http-server-close
option httpclose
reqadd X-Forwarded-Proto:\ https
default_backend appserver
haproxy handles `sni` transparantly based on the requested hostname, if it finds
the certificate in the folder `/etc/ssl/cluster/`. The files there are a
concatenation of the public key, the private key and if needed the certificate
chain.
### Conclusion
In this case it might be better to change the haproxy playbook to handle this,
or to change the group_vars to `all`. However, this environment has certain
constraints set, so this 'suboptimal' workaround works.
[1]: https://raymii.org/s/inc/img/ansible-logo.png
[2]: https://www.digitalocean.com/?refcode=7435ae6b8212
[3]: https://stackoverflow.com/questions/34614337/ansible-get-other-group-vars
[4]: https://docs.ansible.com/ansible/intro_inventory.html#groups-of-groups-and-group-variables
---
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