kiwix-serve will no start if a ZIM failed to be installed.

[letompouce]

TASK [package_management : shell] **********************************************
 [WARNING]: Consider using the file module with state=link rather than running
ln.  If you need to use command because file is insufficient you can add
warn=False to this command task or set command_warnings=False in ansible.cfg to
get rid of this message.
failed: [localhost] (item=maths-et-tiques.fr) => {"changed": true, "cmd": "ln -s /mnt/kiwix/zim/other/la_chaine_de_maths_et_tiques_fr_all_2020-07.zim /var/ideascube/kiwix/maths-et-tiques.fr.zim\n kiwix-manage /var/ideascube/kiwix/library.xml add /var/ideascube/kiwix/maths-et-tiques.fr.zim", "delta": "0:00:00.750560", "end": "2020-09-01 19:24:41.525281", "item": "maths-et-tiques.fr", "msg": "non-zero return code", "rc": 1, "start": "2020-09-01 19:24:40.774721", "stderr": "Invalid /var/ideascube/kiwix/maths-et-tiques.fr.zim : Invalid magic number\nUnable to build or save library file '/var/ideascube/kiwix/library.xml'", "stderr_lines": ["Invalid /var/ideascube/kiwix/maths-et-tiques.fr.zim : Invalid magic number", "Unable to build or save library file '/var/ideascube/kiwix/library.xml'"], "stdout": "", "stdout_lines": []}
changed: [localhost] => (item=bouquineux.fr)
changed: [localhost] => (item=universcience-tv.fr)
changed: [localhost] => (item=biologie-tout-compris.fr)
changed: [localhost] => (item=wikipedia.fr)
changed: [localhost] => (item=cest-pas-sorcier.fr)
changed: [localhost] => (item=nota-bene.fr)
changed: [localhost] => (item=micmaths.fr)
changed: [localhost] => (item=mondial-tissus.fr)
...ignoring

The task reads:

    - shell: |
        ln -s /mnt/kiwix{{ Kiwix.all[item]['url'].split("download.kiwix.org")[-1] }} /var/ideascube/kiwix/{{ item }}.zim
        kiwix-manage /var/ideascube/kiwix/library.xml add /var/ideascube/kiwix/{{ item }}.zim
      with_items: "{{ device_kiwix_pkg }}"
      notify: Start kiwix serve
      ignore_errors: True

Because the task failed, the handler will not be called, and kiwix-serve will not be started.

According to the documentation:

When a task fails on a host, handlers which were previously notified will not be run on that host.

It doesn't explicitely talks about ignore_errors: true, so we can assume handlers will NEVER be called. Which is confirmed by the fact we don't have any HANDLER task at the end of the play.