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I know I can put commands in my source code in .ebextensions/*.config using the commands array. These are executed on every deploy however. What about if I want to execute a configuration command only once when spinning up a new instance?

Gabe Kopley
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2 Answers2

39

Commands can be run conditionally using the test: modifier. You specify a test to be done. If the test returns 0, the command is run, otherwise it is not.

If the last command in your config file touches a file, and the commands above that you only want to run once check for the existence of that file, then those commands will only run the first time.

commands:
  01-do-always:
    command: run_my_script
  02-do-on-boot:
    command: script_to_run_once
    test: test ! -f .semaphore
  99-signal-startup-complete:
    command: touch .semaphore

On Windows it would be something like this

commands:
  01-do-always:
    command: run_my_script
  02-do-on-boot:
    command: script_to_run_once
    test: if exists c:\\path\\to\\semaphore.txt (exit 0) else (exit 1)
  99-signal-startup-complete:
    command: date > c:\\path\\to\\semaphore.txt
Jim Flanagan
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  • How would you do the same thing but on a windows server? How does the syntax differ? Thanks. – SSED Jun 29 '16 at 22:52
  • Updated the post with a Windows example. – Jim Flanagan Jul 05 '16 at 23:02
  • So I guess this applies to the `commands` section, whereas for `container_commands` you could use the `leader-only` option instead? Or did I misinterpret the question? – djvg Sep 17 '18 at 13:52
  • @djvg `leader-only` only executes the command on 1 instance within a target group. The question here is about executing a command on every instance but only once. – Manuel May 03 '20 at 03:38
  • `.semaphore` didn't work for me, I think the current directly is the temporary deployment directory which is erased on every deployment. It worked with a different directory, I decided to use `/var/elasticbeanstalk/...`. – Manuel May 03 '20 at 15:16
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On Windows this should work:

commands:
  01-do-always:
    command: run_my_script
  02-do-on-boot:
    command: script_to_run_once
    test: cmd /c "if exist c:\\semaphore.txt (exit 1) else (exit 0)"
  99-signal-startup-complete:
    command: echo %date% %time% > c:\\semaphore.txt

Note that I had to change the test command from Jim Flanagan's answer.

jmosbech
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