Support for service alias with systemd. (enhancement)

[mapo-job]

Would like the possibility to add an alias in systems script.
This is using a new variable es_service_alias.
Update templates/systemd/elasticsearch.j2, add at the end after WantedBy line:

{% if es_service_alias is defined %}
Alias={{es_service_alias}}.service
{% endif %}

Reason: the current implementation does
- set_fact: instance_init_script={{init_script | dirname }}/{{es_instance_name}}_{{init_script | basename}}
and the service name is nodeName_elasticsearch.service
I want to use the service name elasticsearch instead.

[gingerwizard]

@barryib @jakommo whilst this doesn't quite align with our "package files must be consistent with upstream changes" this is actually potentially really useful. Any objections?

[barryib]

I thinks it's a part of #354 discussion.

[jpcarey]

Although this seems to be very useful, I'd be against allowing further customizations to the unit file that elastic provides (in the spirit of #285). Systemd encourages use of override files, which could be utilized for adding any customizations to the original vendor unit.

systemctl edit elasticsearch.service would create a directory in /etc/systemd/system named after the unit, and an override.conf file in that directory (/etc/systemd/system/elasticsearch.service.d/override.conf)

[gingerwizard]

Several options:

1. We use @jpcarey approach. Possibly we allow the user to provide an override file.
2. Is there a reason why set_fact: is used instead of vars/main.yml? #133 suggests exposing the init/systemd names as variables rather than setting them as facts. Users could then override them. If they don't ensure they are unique this could cause issues with multiple instances on a single host - we'd need to document as i see no easy way to check and validate this (mind you they could easily set instance_name as non unique also).

Thoughts? @jpcarey @barryib @mapo-job

[mapo-job]

I agree that override is a better solution but it did not work for me.
I’m doing the installation and this new variable is not part of the default usage.
So if someone set it, I hope it’s because they read the comment that says it’s for single node per machine.

On CentOS 7 I try to use the override but it did not work.

sudo systemctl edit nodename_elasticsearch.service

#Add content:
[Install]
Alias=
Alias=elasticsearch.service

ls -la /etc/systemd/system/nodename_elasticsearch.service.d/override.conf

-rw-r--r--. 1 root root 45 Aug 22 14:22 /etc/systemd/system/nodename_elasticsearch.service.d/override.conf

sudo systemctl status elasticsearch

Unit elasticsearch.service could not be found.

sudo systemctl daemon-reload
sudo systemctl status elasticsearch

Unit elasticsearch.service could not be found.

sudo systemctl reenable nodename _elasticsearch.service
sudo systemctl status elasticsearch

Unit elasticsearch.service could not be found.

[strootman]

To get around this, I set up my ansible inventory as follows (the names have been changed to protect the innocent);

[elasticsearch-nodes]
hot-1 ansible_host=es1.internet.com
client-1 ansible_host=es1.internet.com
hot-2 ansible_host=es2.internet.com
client-2 ansible_host=es2.internet.com

Next, I override the following variables as follows;

es_instance_name: "{{inventory_hostname_short}}"
instance_suffix: "{{es_instance_name}}"

I'm glazing over a lot of the details, but this is how I use this role to provide multi-node installation/administration. This also bypasses the need to run multiple playbooks for a single host.

[jpcarey]

@mapo-job ah, [Install] can't be used in an override conf, more details on why here: systemd/systemd#1090

The workaround that I found in that issue is to just create the symlink in /etc/systemd/system:

[vagrant@localhost ~]$ sudo ln -s /usr/lib/systemd/system/elasticsearch.service /etc/systemd/system/es.service
[vagrant@localhost ~]$ systemctl status es.service
● elasticsearch.service - Elasticsearch
   Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service; enabled; vendor preset: disabled)
  Drop-In: /etc/systemd/system/elasticsearch.service.d
           └─override.conf
   Active: inactive (dead)
     Docs: http://www.elastic.co

Hope that helps!

[jmlrt]

Hi @mapo-job,
This should be fixed by #566 very soon.

[jmlrt]

#566 is merged.
I'm closing the issue, don't hesitate to reopen it if you have any question.