Override hosts variable of Ansible playbook from the command line

Question

This is a fragment of a playbook that I m using  server yml    - name  Determine Remote User   hosts  web   gather facts  false   roles      -   role  remote-user  tags   remote-user  always      My hosts file has different groups of servers  e g    web  x x x x   droplets  x x x x   Now I want to execute ansible-playbook -i hosts  lt env gt  server yml and override hosts  web from server yml to run this playbook for  droplets    Can I just override as a one time off thing  without editing server yml directly   Thanks

User · Answer

I changed mine to default to no host and have a check to catch it. That way the user or cron is forced to provide a single host or group etc. I like the logic from the comment from @wallydrag. The empty_group contains no hosts in the inventory.

- hosts: "{{ variable_host | default('empty_group') }}"

Then add the check in tasks:

   tasks:
   - name: Fail script if required variable_host parameter is missing
     fail:
       msg: "You have to add the --extra-vars='variable_host='"
     when: (variable_host is not defined) or (variable_host == "")

User · Answer

An other solution is to use the special variable ansible limit which is the contents of the --limit CLI option for the current execution of Ansible   - hosts      ansible limit   default omit        If the --limit option is omitted  then Ansible issues a warning  but does nothing since no host matched    WARNING   Could not match supplied host pattern  ignoring  None  PLAY                                                                  skipping  no hosts matched

User · Answer

I am using ansible 2 5  2 5 3 exactly   and it seems that the vars file is loaded before the hosts param is executed  So you can set the host in a vars yml file and just write hosts     host var    in your playbook  For example  in my playbook yml   --- - hosts      host name       become  yes   vars files      - vars project yml   tasks             And inside vars project yml   ---    general host name  your-fancy-host-name

User · Answer

I m using another approach that doesn t need any inventory and works with this simple command   ansible-playbook site yml -e working host myhost   To perform that  you need a playbook with two plays    first play runs on localhost and add a host  from given variable  in a known group in inmemory inventory second play runs on this known group   A working example  copy it and runs it with previous command    - hosts  localhost   connection  local   tasks    - add host        name      working host           groups  working group     changed when  false  - hosts  working group   gather facts  false   tasks    - debug        msg   I m on    ansible host          I m using ansible 2 4 3 and 2 3 3

User · Answer

Just came across this googling for a solution  Actually  there is one in Ansible 2 5  You can specify your inventory file with --inventory  like this  ansible --inventory configs hosts --list-hosts all

User · Answer

Here s a cool solution I came up to safely specify hosts via the --limit option  In this example  the play will end if the playbook was executed without any hosts specified via the --limit option   This was tested on Ansible version 2 7 10  --- - name  Playbook will fail if hosts not specified via --limit option      Hosts must be set via limit     hosts      play hosts       connection  local   gather facts  false   tasks    - set fact        inventory hosts       - set fact        inventory hosts     inventory hosts    item         with items     hostvars keys   list       - meta  end play     when    play hosts length      inventory hosts length      - debug        msg   About to execute tasks roles for   inventory hostname

User · Answer

This is a bit late  but I think you could use the --limit or -l command to limit the pattern to more specific hosts   version 2 3 2 0   You could have  - hosts  all  or group    tasks    - some task   and then ansible-playbook playbook yml -l some more strict host or pattern and use the --list-hosts flag to see on which hosts this configuration would be applied

User · Answer

If you want to run a task that s associated with a host  but on different host  you should try delegate to   In your case  you should delegate to your localhost  ansible master  and calling ansible-playbook command

User · Answer

I don t think Ansible provides this feature  which it should  Here s something that you can do   hosts      variable host   default  web        and you can pass variable host from either command-line or from a vars file  e g    ansible-playbook server yml --extra-vars  variable host newtarget s

User · Answer

For anyone who might come looking for the solution   Play Book  - hosts      host       tasks    - debug  msg  Host is    ansible fqdn       Inventory   web  x x x x   droplets  x x x x   Command  ansible-playbook deplyment yml -i hosts --extra-vars  host droplets  So you can specify the group name in the extra-vars

User · Answer

We use a simple fail task to force the user to specify the Ansible limit option  so that we don t execute on all hosts by default accident   The easiest way I found is this   --- - name  Force limit      all  is okay here  because the fail task will force the user to specify a limit on the command line  using -l or --limit   hosts   all     tasks    - name  checking limit arg     fail        msg   you must use -l or --limit - when you really want to use all hosts  use -l  all       when  ansible limit is not defined     run once  true   Now we must use the -l    --limit option  when we run the playbook  e g   ansible-playbook playbook yml -l www example com   Limit option docs      Limit to one or more hosts This is required when one wants to run a   playbook against a host group  but only against one or more members of   that group       Limit to one host      ansible-playbook playbooks PLAYBOOK NAME yml --limit  host1        Limit to multiple hosts      ansible-playbook playbooks PLAYBOOK NAME yml --limit  host1 host2       Negated limit    NOTE  Single quotes MUST be used to prevent bash   interpolation       ansible-playbook playbooks PLAYBOOK NAME yml --limit  all  host1       Limit to host group      ansible-playbook playbooks PLAYBOOK NAME yml --limit  group1

[ansible] Override hosts variable of Ansible playbook from the command line

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