Conditionals

Where a conditional will run a command (e.g. to check the outcome of an onlyif statement) Tacoscript will use the shell parameter to determine the shell to run the command with.

creates parameter can have both string and array type.

backup-data:
  cmd.run:
    - name: echo 123
    - creates:
        - file1.txt
        - file2.txt

or

backup-data:
  cmd.run:
    - name: echo 123
    - creates: file1.txt

The creates parameter identifies the files which should be missing if you want to run the current task. In other words if any of the files in the creates section exist, the task will never run.

A typical example use case for this parameter would be an exclusive access to a file, e.g. we don’t run the backup, if the file is locked by another process:

backup-data:
  cmd.run:
    - names:
        - touch serviceALock.txt
        - tar cvf somedata.txt.tar somedata.txt
        - rm serviceALock.txt
    - creates: serviceALock.txt

In this situation we expect that the script is running periodically, so at some point the lock will be removed, and the backup-data script get a chance to make a backup.

The onlyif parameter gives a list of commands which will be executed before the actual task and if any of them fails ( returns non zero exit code), the task will be skipped. However, the failures won’t stop the program execution. The onlyif checks are given to prove that the task should run, in case of failure the task will be completely ignored.

In the example below the command kafka-console-producer.sh --broker-list localhost:9092 --topic my_topic --new-producer < my_file.txt won’t be triggered, if tacoscript detects, that kafka or zookeeper services are not running or messages.txt file doesn’t exist.

onlyif parameter can be both string and array e.g.

publish-kafka-message:
  cmd.run:
    - name: kafka-console-producer.sh --broker-list localhost:9092 --topic my_topic --new-producer < my_file.txt
    - onlyif: test -e my_file

or

publish-kafka-message:
  cmd.run:
    - name: kafka-console-producer.sh --broker-list localhost:9092 --topic my_topic --new-producer < messages.txt
    - onlyif:
        - service kafka status
        - service zookeeper status
        - test -e messages.txt

The unless is a reverted onlyif parameter which means the task will run only of the unless condition fails ( returns a non-zero exit code). However if multiple unless parameters are used, tacoscript will execute the task only if one unless condition fails (the onlyif parameters should be all successful to unblock the task).

The examples below show some use cases for this parameter. We execute the command service myservice start only if we detect that there are no critical logs. Without this condition tacoscript will try to start the service which has no chance to be started.

start-myservice:
  cmd.run:
    - name: service myservice start
    - unless: test -e myservice_fatallogs.txt

The second example demonstrates a check for some required configs. If the tacoscript detects any missing config from the list, it will send an email to the server’s adminstrator.

report-failure:
  cmd.run:
    - name: mail -s "Some configs are missing, check what is going on" admin@admin.com
    - unless:
        - test -e criticalConfigOne.txt
        - test -e criticalConfigTwo.txt
        - test -e criticalConfigThree.txt