Is there an elegant way to check file integrity with md5 in ansible using md5 files fetched from server?

If you wish to go with your method of storing the checksum in files on the server, you can definitely use the get_url checksum arg to validate it.

Download the .md5 file and read it into a var:

- set_fact:
    md5_value: "{{ lookup('file', '/etc/myfile.md5') }}"

And then when you download the file, pass the contents of md5_value to get_url:

- get_url:
    url: http://example.com
    dest: /my/dest/file
    checksum: "md5:{{ md5_value }}"
    force: true

Note that it is vital to specify a path to a file in dest; if you set this to a directory (and have a filename in url), the behavior changes significantly.

Note also that you probably need the force: true. This will cause a new file to download every time you run it. The checksum is only triggered when files are downloaded. If the file already exists on your host it won't bother to validate the sum of the existing file, which might not be desirable.

To avoid the download every time you could stat to see if the file already exists, see what its sum is, and set the force param conditionally.

- stat:
    path: /my/dest/file
  register: existing_file

- set_fact:
    force_new_download: "{{ existing_file.stat.md5 != md5_value }}"
  when: existing_file.stat.exists

- get_url:
    url: http://example.com
    dest: /my/dest/file
    checksum: "md5:{{ md5_value }}"
    force:  "{{ force_new_download | default ('false') }}"

Also, if you are pulling the sums/artifacts from some sort of web server you can actually get the value of the sum right from the url without having to actually download the file to the host. Here is an example using a Nexus server that would host the artifacts and their sums:

- set_fact:
    md5_value: "{{ item }}"
  with_url: http://my_nexus_server.com:8081/nexus/service/local/artifact/maven/content?g=log4j&a=log4j&v=1.2.9&r=central&e=jar.md5

This could be used in place of using get_url to download the md5 file and then using lookup to read from it.

With the stat module:

- stat:
    path: "path/to/your/file"
  register: your_file_info

- debug:
    var: your_file_info.stat.md5