The retries parameter can be used to retry a task. In this example, you want to retry the ps command 3 times. The retries option is often used with the delay option.

---
- hosts: localhost
  tasks:
  - name: ps command
    shell: "ps -ef | grep httpd"
    retries: 3
    delay: 3
    register: out
    until: out.rc == 0
...

In this example, the return code of the ps command will be 0 (success) when there is an HTTPD process running on the managed node (e.g. target system). On the other hand, the return code will be 1 (failed) when there are no HTTPD processes running on the managed node. In this example, as long as the return code is not 0, the ps command will be retried 3 times.

Running this play should produce the following.

PLAY [all] 

TASK [ps command] 
FAILED - RETRYING: ps command (3 retries left).
FAILED - RETRYING: ps command (2 retries left).
FAILED - RETRYING: ps command (1 retries left).
fatal: [localhost]: FAILED! => {"attempts": 3, "changed": true, "cmd": "ps -ef | grep httpd", "delta": "0:00:00.014413", "end": "2020-07-20 05:23:37.348236", "msg": "non-zero return code", "rc": 1, "start": "2020-07-20 05:23:37.333823", "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}

PLAY RECAP 
localhost : ok=1    changed=0    unreachable=0    failed=1