Python to emulate remote tail -f?

Question

We have several application servers, and a central monitoring server.

We are currently running ssh with \"tail -f\" from the monitoring server to stream several text

Answer 1

I wrote a function that do that:

import paramiko
import time
import json

DEFAULT_MACHINE_USERNAME="USERNAME"
DEFAULT_KEY_PATH="DEFAULT_KEY_PATH"

def ssh_connect(machine, username=DEFAULT_MACHINE_USERNAME,
                key_filename=DEFAULT_KEY_PATH):
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    ssh.connect(hostname=machine, username=username, key_filename=key_filename)
    return ssh

def tail_remote_file(hostname, filepath, key_path=DEFAULT_KEY_PATH,
                     close_env_variable="CLOSE_TAIL_F", env_file='~/.profile'):
    ssh = ssh_connect(hostname, key_filename=key_path)

    def set_env_variable(to_value):
        to_value_str = "true" if to_value else "false"
        from_value_str = "false" if to_value else "true"
        ssh.exec_command('sed -i \'s/export %s=%s/export %s=%s/g\' %s' %
                         (close_env_variable, from_value_str,
                          close_env_variable, to_value_str, env_file))
        time.sleep(1)

    def get_env_variable():
        command = "source .profile; echo $%s" % close_env_variable
        stdin, stdout_i, stderr = ssh.exec_command(command)
        print(command)
        out = stdout_i.read().replace('\n', '')
        return out

    def get_last_line_number(lines_i, line_num):
        return int(lines_i[-1].split('\t')[0]) + 1 if lines_i else line_num

    def execute_command(line_num):
        command = "cat -n %s | tail --lines=+%d" % (filepath, line_num)
        stdin, stdout_i, stderr = ssh.exec_command(command)
        stderr = stderr.read()
        if stderr:
            print(stderr)
        return stdout_i.readlines()

    stdout = get_env_variable()
    if not stdout:
        ssh.exec_command("echo 'export %s=false' >> %s" %
                         (close_env_variable, env_file))
    else:
        ssh.exec_command(
            'sed -i \'s/export %s=true/export %s=false/g\' %s' %
            (close_env_variable, close_env_variable, env_file))
    set_env_variable(False)

    lines = execute_command(0)
    last_line_num = get_last_line_number(lines, 0)

    while not json.loads(get_env_variable()):
        for l in lines:
            print('\t'.join(t.replace('\n', '') for t in l.split('\t')[1:]))
        last_line_num = get_last_line_number(lines, last_line_num)
        lines = execute_command(last_line_num)
        time.sleep(1)

    ssh.close()