# Creating /etc/hosts from ansible hosts **URL:** \ **Category:** Ansible Project\ **Tags:** kubernetes\ **Created:** [October 27, 2019, 2:49am UTC](https://forum.ansible.com/t/creating-etc-hosts-from-ansible-hosts/31549 "2019-10-27T02:49:18Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![budhac](https://avatars.discourse-cdn.com/v4/letter/b/ebca7d/32.png) [@budhac](https://forum.ansible.com/u/budhac)\ **Post date:** [October 27, 2019, 2:49am UTC](https://forum.ansible.com/t/creating-etc-hosts-from-ansible-hosts/31549/1 "2019-10-27T02:49:18Z")
I am trying to figure out if there is a way to use Ansible to automate the creation of /etc/hosts files depending on which group the Ansible host belongs to. I am creating multiple test Kubernetes clusters that will use hosts files for DNS resolution. ` [Group 1] kube-g1-master1 ansible\_host=10.90.1.11 kube-g1-master2 ansible\_host=10.90.1.12 kube-g1-master3 ansible\_host=10.90.1.13 kube-g1-node1 ansible\_host=10.90.1.14 kube-g1-node2 ansible\_host=10.90.1.15 kube-g1-lb ansible\_host=10.90.1.16 [Group 2] kube-g2-master1 ansible\_host=10.90.1.21 kube-g2-master2 ansible\_host=10.90.1.22 kube-g2-master3 ansible\_host=10.90.1.23 kube-g2-node1 ansible\_host=10.90.1.24 kube-g2-node2 ansible\_host=10.90.1.25 kube-g2-lb ansible\_host=10.90.1.26 [Group 3] kube-g3-master1 ansible\_host=10.90.1.31 kube-g3-master2 ansible\_host=10.90.1.32 kube-g3-master3 ansible\_host=10.90.1.33 kube-g3-node1 ansible\_host=10.90.1.34 kube-g3-node2 ansible\_host=10.90.1.35 kube-g3-lb ansible\_host=10.90.1.36 etc… ` When I use **[all]**, as Ansible iterates through the hosts file can it search which Group the host belongs to and create an **/etc/hosts** from the group hostnames and IPs. For example: 1. Ansible interacts with: **kube-g2-master3** ` inventory\_hostname = kube-g2-master3 ` 1. Finds **kube-g2-master3** belongs **[Group 2]** 2. Creates **/etc/hosts** on **kube-g2-master3** using the **inventory\_hostname** and **ansible\_hosts** from **[Group 2]** ` /etc/hosts kube-g2-master1 10.90.1.21 kube-g2-master2 10.90.1.22 kube-g2-master3 10.90.1.23 kube-g2-node1 10.90.1.24 kube-g2-node2 10.90.1.25 kube-g2-lb 10.90.1.26 ` Thanks for any help. ---
**Author:** ![Kai\_Stian\_Olstad](https://avatars.discourse-cdn.com/v4/letter/k/e19adc/32.png) [@Kai\_Stian\_Olstad](https://forum.ansible.com/u/Kai_Stian_Olstad)\ **Post date:** [October 27, 2019, 7:48am UTC](https://forum.ansible.com/t/creating-etc-hosts-from-ansible-hosts/31549/2 "2019-10-27T07:48:14Z")
> I am trying to figure out if there is a way to use Ansible to automate the > creation of /etc/hosts files depending on which group the Ansible host > belongs to. I am creating multiple test Kubernetes clusters that will use > hosts files for DNS resolution. > > [Group 1] > kube-g1-master1 ansible\_host=10.90.1.11 > kube-g1-master2 ansible\_host=10.90.1.12 > kube-g1-master3 ansible\_host=10.90.1.13 > kube-g1-node1 ansible\_host=10.90.1.14 > kube-g1-node2 ansible\_host=10.90.1.15 > kube-g1-lb ansible\_host=10.90.1.16 > [Group 2] > kube-g2-master1 ansible\_host=10.90.1.21 > kube-g2-master2 ansible\_host=10.90.1.22 > kube-g2-master3 ansible\_host=10.90.1.23 > kube-g2-node1 ansible\_host=10.90.1.24 > kube-g2-node2 ansible\_host=10.90.1.25 > kube-g2-lb ansible\_host=10.90.1.26 > [Group 3] > kube-g3-master1 ansible\_host=10.90.1.31 > kube-g3-master2 ansible\_host=10.90.1.32 > kube-g3-master3 ansible\_host=10.90.1.33 > kube-g3-node1 ansible\_host=10.90.1.34 > kube-g3-node2 ansible\_host=10.90.1.35 > kube-g3-lb ansible\_host=10.90.1.36 > etc... > > When I use\* [all]\*, as Ansible iterates through the hosts file can it > search which Group the host belongs to and create an\* /etc/hosts\* from the > group hostnames and IPs. Space in group names is not allowed. > For example: > > 1. Ansible interacts with: \*kube-g2-master3\* > > inventory\_hostname = kube-g2-master3 > > 2. Finds \*kube-g2-master3\* belongs\* [Group 2]\* Groups in Ansible is just for grouping variables, and the grouping is lost when Ansible is running. What you can do is check if a host is in a group, but you would need to check every group.    when: "'kube-g2-master3' in groups['group2']" And the list of all group is in the special variable "group\_names". > 3. Creates \*/etc/hosts\* on \*kube-g2-master3\* using the \*inventory\_hostname\* > and \*ansible\_hosts\* from\* [Group 2]\* > > /etc/hosts > > kube-g2-master1 10.90.1.21 > kube-g2-master2 10.90.1.22 > kube-g2-master3 10.90.1.23 > kube-g2-node1 10.90.1.24 > kube-g2-node2 10.90.1.25 > kube-g2-lb 10.90.1.26 Since you are building a host list, all you need in the variable groups['group2'] this is a list of all members in that group. ---
**Author:** ![vbotka](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/vbotka/32/359_2.png) [@vbotka](https://forum.ansible.com/u/vbotka)\ **Post date:** [October 27, 2019, 10:35am UTC](https://forum.ansible.com/t/creating-etc-hosts-from-ansible-hosts/31549/3 "2019-10-27T10:35:15Z")
Use "group\_names: List of groups the current host is part of" [https://docs.ansible.com/ansible/latest/reference\_appendices/special\_variables.html](https://docs.ansible.com/ansible/latest/reference_appendices/special_variables.html) It's possible to create lists of [host, ip]. For example (given a host may be a member of multiple groups) the tasks below   - set\_fact:       my\_hosts: "{{ my\_hosts|default() +                     groups[item]|                     zip(groups[item]|                     map('extract', hostvars, 'ansible\_host')|list)| list }}"     loop: "{{ group\_names }}"     - set\_fact:         my\_hosts: "{{ my\_hosts|unique }}" give     "my\_hosts": [         [             "test\_01",             "10.1.0.51"         ],         [             "test\_02",             "10.1.0.52"         ],         [             "test\_03",             "10.1.0.53"         ]     ] Then create /etc/hosts. For example     - template:         src: hosts.j2         dest: /tmp/hosts   $ cat hosts.j2   {% for item in my\_hosts %}   {{ item.0 }} {{ item.1 }}   {% endfor %} Cheers,   -vlado