Ansible wait_for module, start at end of file

Question

With the wait_formodule in Ansible if I use search_regex='foo' on a file

it seems to start at the beginning of the file, which means it will match on old data, thus when restarting a process/app (Java) which appends to a file rather than start a new file, the wait_for module will exit true for old data, but I would like to check from the tail of the file.

Answer 1

Regular expression in search_regex of wait_for module is by default set to multiline.

You can register the contents of the last line and then search for the string appearing after that line (this assumes there are no duplicate lines in the log file, i.e. each one contains a time stamp):

vars:
  log_file_to_check: <path_to_log_file>
  wanted_pattern: <pattern_to_match>

tasks:
  - name: Get the contents of the last line in {{ log_file_to_check }}
    shell: tail -n 1 {{ log_file_to_check }}
    register: tail_output

  - name: Create a variable with a meaningful name, just for clarity
    set_fact:
      last_line_of_the_log_file: "{{ tail_output.stdout }}"

  ### do some other tasks ###

  - name: Match "{{ wanted_pattern }}" appearing after "{{ last_line_of_the_log_file }}" in {{ log_file_to_check }}
    wait_for:
      path: "{{ log_file_to_check }}"
      search_regex: "{{ last_line_of_the_log_file }}\r(.*\r)*.*{{ wanted_pattern }}"