Ansible lineinfile regexp to manage /etc/exports - regex

Question

I've been hitting a wall trying to get /etc/exports managed via Ansible.
I've got a role that installs a piece of software on a VM, and I want to then add an entry ot /etc/exports on the NFS server, for that specific VM, so it's able to access the NFS shares needed.
Lineinfile sounds like the way to go, but sofar I can't figure out how to properly write this.
I want this to:
not modify if the host is in the line, no matter where
add the NFS share and the host if there's no line for the NFS share
add the host to the share in case it isn't in there.
The latest installment of my 'add to /etc/exports' that thought should work, but doesn't, is:
- name: Add hosts to mountpoint line
ansible.builtin.lineinfile:
path: /etc/exports
line: '\1 {{ host_ip }}(root_squash,no_subtree_check)'
regex: '^((?!{{ volume_mountpoint }}.*{{ host_ip }}\(root_squash,no_subtree_check\).*).*)$'
backrefs: yes
but i'm still getting all kinds of weird side effects. I've used backreferences etc before, but somehow this one keeps tripping me up.
Anyone who sees what's gong wrong?
Typical /etc/exports entry:
/srv/files 172.16.0.14(rw,no_root_squash,no_subtree_check)

Answer 1

It's not possible in one step to modify a line using backreferences or add the line if missing. To modify the existing mount point the back-references are needed. For example, given the files for testing
shell> cat etc/export1
/srv/files 172.16.0.14(rw,no_root_squash,no_subtree_check)
shell> cat etc/export2
/srv/files 172.16.0.15(rw,no_root_squash,no_subtree_check)
shell> cat etc/export3
/srv/download 172.16.0.14(rw,no_root_squash,no_subtree_check)
the task
tasks:
- lineinfile:
path: "etc/{{ item }}"
regex: '^{{ mount }}(\s+)({{ ipr }})*({{ optionsr }})*(\s*)(.*)$'
line: '{{ mount }}\g<1>{{ ip }}{{ options }} \g<5>'
backrefs: true
vars:
mount: /srv/files
ipr: '172\.16\.0\.14'
ip: '172.16.0.14'
optionsr: '\(.*?\)'
options: '(root_squash,no_subtree_check)'
loop:
- export1
- export2
- export3
gives
--- before: etc/export1 (content)
+++ after: etc/export1 (content)
## -1 +1 ##
-/srv/files 172.16.0.14(rw,no_root_squash,no_subtree_check)
+/srv/files 172.16.0.14(root_squash,no_subtree_check)
changed: [localhost] => (item=export1)
--- before: etc/export2 (content)
+++ after: etc/export2 (content)
## -1 +1 ##
-/srv/files 172.16.0.15(rw,no_root_squash,no_subtree_check)
+/srv/files 172.16.0.14(root_squash,no_subtree_check) 172.16.0.15(rw,no_root_squash,no_subtree_check)
changed: [localhost] => (item=export2)
ok: [localhost] => (item=export3)
The first two files are all right. The problem is the third file. The line hasn't been added to the file. Quoting from backrefs
"... if the regexp does not match anywhere in the file, the file will be left unchanged."
The explanation is simple. There are no groups if the regex doesn't match. If there are no groups the line can't be created.
On the other hand, quoting from regexp
"... If the regular expression is not matched, the line will be added to the file ..."
As a result, it's not possible to ask lineinfile to add a line if the regexp does not match and, at the same time, to do nothing if the regexp is matched. If the regexp is matched you need back-references. If you use back-references you can't add a missing line.
To solve this problem read the content of the files and create a dictionary
- command: "cat etc/{{ item }}"
register: result
loop: [export1, export2, export3]
- set_fact:
content: "{{ dict(_files|zip(_lines)) }}"
vars:
_lines: "{{ result.results|map(attribute='stdout_lines')|list }}"
_files: "{{ result.results|map(attribute='item')|list }}"
gives
content:
export1:
- /srv/files 172.16.0.14(rw,no_root_squash,no_subtree_check)
export2:
- /srv/files 172.16.0.15(rw,no_root_squash,no_subtree_check)
export3:
- /srv/download 172.16.0.14(rw,no_root_squash,no_subtree_check)
Now add the line only if missing, i.e. do not replace the line if the mount point is already there
- lineinfile:
path: "etc/{{ item }}"
line: '{{ mount }} {{ ip }}{{ options }}'
vars:
mount: /srv/files
ip: '172.16.0.14'
options: '(root_squash,no_subtree_check)'
loop: "{{ content|list }}"
when: content[item]|select('search', mount)|length == 0
gives
skipping: [localhost] => (item=export1)
skipping: [localhost] => (item=export2)
--- before: etc/export3 (content)
+++ after: etc/export3 (content)
## -1 +1,2 ##
/srv/download 172.16.0.14(rw,no_root_squash,no_subtree_check)
+/srv/files 172.16.0.14(root_squash,no_subtree_check)