How can I check for file existence in salt file server - salt-stack

Question

I want to copy ssh keys for users automatically, some users do not have keys.
What I have now is:
ssh_auth:
- present
- user: {{ usr }}
- source: salt://users/keys/{{usr}}.id_rsa.pub
When a key for a user does not exist on salt:// fileserver, I get an error. Is there some function to check for existence of a file in salt:// fileserver?

Answer 1

If you feel you MUST learn how to do this with just states, you can use the fallback mechanism by specifying a list of sources:
From the docs:
ssh_auth:
- present
- user:{{usr}}
- source:
- salt://users/keys/{{usr}}.id_rsa.pub
- salt://users/keys/null.id_rsa.pub
Where cat /dev/null > /srv/salt/users/keys/null.id_dsa.pub
Professionally, user keys should be stored in pillars. This presents the additional functionality that pillars are stored and retrieved from the master at execution time - which means you can test for the existence of the file per your original request. I do something just like that for openvpn certificates:
http://garthwaite.org/virtually-secure-with-openvpn-pillars-and-salt.html

Answer 2

I don't know of a jinja or salt function which can check the master's file server for a specific file. I would recommend you put those keys as a key in the pillar's file which contains your user's and use jinja to detect the existence of that key and create the key when necessary. For example:
The pillars file:
# Name of file : user_pillar.sls
users:
root:
ssh_key: some_key_value
home : /root
createhome: True
The state file:
# Name of file : users_salt_state_file.sls
{% for user,args in salt['pillar.get']('users',{}).iteritems() %}
# Ensure user is present
{{ user }}_user:
user.present:
- name: {{ user }}
# Home Creation
{% if args and 'home' in args %}
- home: {{ args['home'] }}
{% endif %}
{% if args and 'createhome' in args %}
- createhome: {{ args['createhome'] }}
{% endif %}
# SSH_auth
{% if args and 'ssh_key' in args %}
{{ args['ssh_key'] }}
ssh_auth:
- present
- user: {{ user }}
{% endfor %}