CRON

The configuration file used for crontab is <PROJECT ROOT>/clevercloud/cron.json.

Syntax

Here is the general syntax:

[
  "<string>",
  "<string>"
]

The string <string> must use the cron format:

M H d m Y command

• M: Minute [0,59]
• H: Hour [0,23]
• d: Day of the month [1,31]
• m: Month of the year [1,12]
• Y: Day of the week [0,6] (0 is Sunday)

For more information about the syntax, you can check the Wikipedia page of cron.

Restrictions

There are two restrictions about the usage of crontab on our platform:

• The special date @reboot is not available since the crontab is added after the startup of the instance
• You must use the absolute path of commands

$ROOT

You can use the special token $ROOT to refer to the root folder of your application.

Example of clevercloud/cron.json which executes the file cron.php every 5 minutes:

[
  "*/5 * * * * /usr/bin/php $ROOT/cron.php"
]

Note: $ROOT is only a token (not an actual variable) which is replaced when setting up the crons by the equivalent of the APP_HOME variable (/home/bas/<app_id>). Do not write ${ROOT}, only $ROOT will work.

Access environment variables

To have access to environment variable, you must wrap your commands in a bash script. Let’s say your command is bundle exec rake myapp:dosomething.

You need to put it in a bash script, starting with #!/bin/bash -l. The -l is very important:

#! /bin/bash -l

cd ${APP_HOME} # Which has been loaded by the env.
bundle exec rake myapp:dosomething

Then you need to commit an executable file:

chmod +x crons/mycron.sh
git add crons/mycron.sh

git diff --cached
$ diff --git a/crons/mycron.sh b/crons/mycron.sh
$ old mode 100644
$ new mode 100755

git commit -m "Make cron file executable"

Then, in clevercloud/cron.json:

[
  "*/5 * * * * $ROOT/crons/mycron.sh"
]

Avoiding double bash

You might be tempted to put the following in your cron.json file:

[
  "*/5 * * * * /bin/bash $ROOT/crons/mycron.sh"
]

Do NOT do this. Invoking bash here will supersede the shebang and cancel the bash -l that loads the env. So just put the path to your executable mycron.sh.

You can refer to this list to see which variables are available.

Deduplicating crons

Crons are installed and executed on every scaler of an application. This means the same cron may be executed more than once.

You can use your own techniques to avoid that, like a shared task queue or some other locking system.

If you do want to stay stateless and simple, just your bash wrapper script by:

#! /bin/bash -l

if [[ "$INSTANCE_NUMBER" != "0" ]]; then
  echo "Instance number is ${INSTANCE_NUMBER}. Stop here."
  exit 0
fi

cd ${APP_HOME} # Which has been loaded by the env.
# Your part here

Logs collection

Everything coming from stdout & stderr is forwarded to our logs collection system and is available in the web console / CLI logs.