How to start/end a background process from PHP/bash script?

Question

I have a service where I list Twitter accounts and have a switch to enable/disable a Streaming API connection for them.

Currently I'm planning to have this flow:

• User enables a Twitter account for Streaming
• An email is sent to an admin with cli access on the server, who launches a Phirehose process for that account.
• (A cron job takes a list of Twitter accounts that have Streaming enabled and checks if a process exists for them. If not, it sends an email to the admin who can relaunch it.)

I would like to launch a Phirehose process directly to run in the background when a user wants a Twitter account to be enabled for Streaming. Also I would like to kill the process directly if a user wants to stop Streaming for that account.

There are several risks and concerns with executing the Phirehose process and especially killing it in an automated way.

Any tips on the best way to implement this with maximal automation and minimal admin interference?

Answer 1

I have done similar things with a two step process: part one is to create a web interface that provides start / stop commands. The web interface writes a file to the server. one for start, one for stop. start.lock, stop.lock.

the second part is a bash script that looks for the presence of these files. Below is an example of the start.sh script that would check to start the service. It creates a a "running.lock" file to know not to try to start a running service. You cazn also use the files for reporting purposes.

stop.sh and start.sh are cron scheduled to run frequently. For my purpose, they run every minute and the loop in the script is used to check more frequently. ie, each minute run and check 5 times once every ten seconds.

I think with this you can modify to your specific needs. Hope it helps.

#!/bin/bash

for ((c=1; c<=5; c++))
do

file="start.lock"
if [ -f "$file" ]
then
        sfile="running.lock"
        if [ ! -f "$sfile" ]
        then
                <command goes here>
                touch running.lock
                rm start.lock
        fi

fi

sleep 10
done

and to stop it:

#!/bin/bash

for (( c=1; c<=11; c++ ))
do
file="stop.lock"
if [ -f "$file" ]
then
        killall -9 <your service>
        rm running.lock
        rm start.lock
        rm stop.lock
fi
sleep 5
done

Answer 2

I'm currently using the following script to keep a phirehose process always running. I want to be able to control it from php, so I wrote the launcher script also in php instead of bash.

I added a little code to let me know what type of error, or non-error occurred, but always try to reconnect.

phirehose-launcher.php:

<?php 

while(1) {
    passthru('/usr/bin/php my-phirehose-script.php', $code);

    // if exits with error, show error but try to reconnect
    if ($code) {
        print "Encountered an error.\n";
        print "Return code: $code.\n";
        print "Waiting 5 seconds and will retry connection.\n";
        sleep(5);
    } else {
        // if Phirehose exits gracefully, restart it
        print "Script exited. Restarting.\n";
    }

    // Try again in 5 secs
    sleep(5);
}

If you want to make it run in the background, I haven't tried this but it should work to add a & after the script name either in the launcher (as in the code below) or to the launcher script itself.

    passthru('/usr/bin/php my-phirehose-script.php &', $code);

In my PhirehoseConsumer class I overwrote the log method to manicure the output for logging.

protected function log($message,$level='notice')
{
    switch($level) {
        case 'error':
            print "Phirehose [ERROR]: $message\n";
            break;
            // should email these or text
        case 'info':
            print "Phirehose [INFO]: $message\n";
            break;
        case 'notice':
        default:
            // meh
            break;
    }
}

Instead of the script exiting, I see logged output like this:

Phirehose [INFO]: Idle timeout: No stream activity for > 90 seconds.  Reconnecting.

You can kill the launcher php script and the child process is killed. Which is an easy way to control the process. And it catches idle timeouts and exits from phirehose so that the process keeps running even if streaming is interrupted or internet connectivity.