Wake Up

Wake Up is a Node script that sends an HTTP get request to a website and logs a few basic metrics about the site's response. It is meant to be configured as a cron job.

Motivation

Many developers host their side projects on Heroku. Heroku offers a free tier which provides a capped number of free hours per month, but one of the limitations is that your app will go to sleep after 30 minutes if it doesn't receive any traffic (see Heroku Pricing). Waking a sleeping app involves starting the dyno (i.e. Linux container) the app is running on. Just like starting your own computer, this takes several seconds. If you're a web developer and demonstrating your website to a potential client or employer, having it take 10 seconds to load is a problem.

So, then, how can you prevent your app from sleeping?

There are several websites out there that claim to keep your Heroku app awake for you. Just give them your URL, and they will ping your site periodically. I didn't want to go this route, however, for a couple reasons. First, I didn't want to give a third-party control over how often my dyno is running. Since I have a limited number of hours per month, and I could potentially have several apps running on the free tier at any one time, I didn't want any single app to have insomnia and burn through most of my hours. Second, as a relative newcomer to the Ubuntu operating system, I had never set up a cron job, and I saw this as a wonderful opportunity to learn how.

Getting Starting

Simply download the wakeUp.js file and run it with Node. It takes one argument, the URL for the website you want to request. Be sure to include the scheme (http or https).

From the command line:

$ node wakeUp.js http://www.example.com/

The script will write a few metrics from the request to a log file. Each line of ouput has the following format:

Date, time, URL, res-status-code, res-time, res-body-size

If there is an error, the script will log the date, time, and an error message.

By default, the log file is named wakeUp.js.log and will be in the same directory as the script. If you wish to change the name or location of the log file, simply edit the value of logFile in the function logMessage.

Configuring a Cron Job

Ubuntu and macOS

You can set up a cron job by using the crontab program. To add your job, enter crontab -e at the command line. You'll now be editing the file that contains the cron jobs for your user account.

The syntax of a crontab command looks like this:

t1 t2 t3 t4 t5 path/to/command arg1 arg2 ... argN

where...

t1 is minutes from 0-59,
t2 is hours from 0-23 (midnight = 0),
t3 is days from 1-31,
t4 is months from 1-12, and
t5 is days of the week from 0-6 (Sunday = 0)

and...

an asterisk (*) in any field means every period
a dash (-) means a range of values
a forward slash (/) means an increment.

For my cron job, I decided to have it run every 10 minutes. Here is what my crontab file looks like:

PATH = /usr/bin:/bin:/path/to/node/bin
*/10 * * * * node /path/to/wakeUp.js http://www.example.com

A few things to note here...

On line 1, I appended to PATH the path to the folder which contains the Node executable. This is necessary so that the cron daemon knows where to find the name node on line 2. To find the path to your version of Node, enter which node on the command line. Alternatively, rather than defining PATH on line 1, you could just give the absolute path to the Node executable on line 2, i.e. replace node with /path/to/node.
*/10 * * * * means to run the job every 10 minutes every day of the year. If I wanted it to run every 30 minutes, I would do */30 * * * *. If I wanted it to run every 10 minutes on weekdays only, I would do */10 * * * 1-5.
The third line is empty. Each command in the crontab file must end in a newline character or it won't work.

After saving and closing the crontab file, you can go back to the folder that contains the wakeUp.js script and look for the log file. If the cron job is working properly, you will see new entries to the file at the increment that you specified.

If it's not working, and you're on Ubuntu, you might check /var/log/syslog to see if the job is running. Specifically, try $ grep CRON /var/log/syslog to view only the logs related to cron. I don't believe macOS logs cron jobs by default, however.

Windows

The easiest way to set up a cron job on Windows is with the "Task Scheduler" app. Here are the steps to take:

Go to "Start" > "Windows Administrative Tools" > "Task Scheduler", or go to "Start" and type "Task Scheduler".
Once the app opens, right click the Task Scheduler Library folder in the left pane and select New Folder.... Name the folder whatever you'd like, e.g. "My Tasks". This isn't a required step, but it helps keep the operating system tasks separate from your own.
Select your newly created folder, and then go to the menu bar and select Action > Create Task....
On the General tab, give your task a name and description. The other defaults are fine.
On the Triggers tab, select the New... button at the bottom. For the Begin the task: dropdown, select On a schedule. Next, select the One time radio button. In Advanced Settings, select the checkbox for Repeat task every: and change the time whatever increment you would like. (Just make sure it's less than 30 minutes if you want to keep your dyno awake.) Then change for duration of: to Indefinitely.
On the Actions tab, select Start a program. Enter the address to the Node executable in the Program/script input box. Make sure to wrap the address in quotes if it contains spaces, e.g. "C:\Program Files\nodejs\node.exe". For the arguments input box, enter the address to the script and the website you want to keep awake. I entered C:\Projects\wake_up\wakeUp.js http://www.example.com. (Note the space between the two arguments.)
On the Conditions tab, the defaults are fine.
On the Settings tab, I checked the box for Run task as soon as possible after a scheduled start is missed and left the others as default.
Finally, click OK to finish creating the task, and you should be good to go!

You can check the wakeUp.js.log file to make sure your task is running properly. If not, double check your arguments on the Actions tab and the schedule on the Triggers tab. Those are the two areas that gave me trouble.

Author

Michael Singhurse
michaelsinghurse@gmail.com