Before the instance was vulnerable to an OTA update while processing a
request. Because there is no way of retriggering a job in Composer, it
is better to avoid this situation.
The way we are doing it is by setting the `protected` flag onto the
instance when a job is being processed. This way the AWS scheduler
does hopefully not shutdown the machine at the wrong time.
Main caveats of this solution:
* Starvation: If a worker keeps accepting new jobs, then it might not be
updated.
* Inconsistency: There exist a window between the job acceptation and the
protection where the worker can be shutdown without having the time to
protect itself.
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