Support graceful cancellation #332
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Adjust cmd_default so that it kills the process on context cancellation
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This is an alternative to hashicorp#332, adding an option that enables the user to implement graceful shutdowns for Apply and Destroy operations. Rather than adding an option that changes the behavior of the input context, we instead add an option that specifically sends an interrupt to the terraform process. The input context behavior remains unchanged. This requires the caller to do a bit more orchestration work for timeouts, but keeps context truer to the "abandon work" intent. This also allows users to force quit _even if_ they are in the middle of a graceful shutdown, rathern than having one behavior mutually exclusive with the other.
twmb
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This is an alternative to hashicorp#332, adding an option that enables the user to implement graceful shutdowns for Apply and Destroy operations. Rather than adding an option that changes the behavior of the input context, we instead add an option that specifically sends an interrupt to the terraform process. The input context behavior remains unchanged. This requires the caller to do a bit more orchestration work for timeouts, but keeps context truer to the "abandon work" intent. This also allows users to force quit _even if_ they are in the middle of a graceful shutdown, rathern than having one behavior mutually exclusive with the other.
twmb
added a commit
to redpanda-data/terraform-exec
that referenced
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Aug 31, 2022
This is an alternative to hashicorp#332, adding an option that enables the user to implement graceful shutdowns for Apply and Destroy operations. Rather than adding an option that changes the behavior of the input context, we instead add an option that specifically sends an interrupt to the terraform process. The input context behavior remains unchanged. This requires the caller to do a bit more orchestration work for timeouts, but keeps context truer to the "abandon work" intent. This also allows users to force quit _even if_ they are in the middle of a graceful shutdown, rathern than having one behavior mutually exclusive with the other.
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Closing in favor of #334 which is a much simpler and nicer implementation |
twmb
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Sep 1, 2022
This is an alternative to hashicorp#332, adding an option that enables the user to implement graceful shutdowns for Apply and Destroy operations. Rather than adding an option that changes the behavior of the input context, we instead add an option that specifically sends an interrupt to the terraform process. The input context behavior remains unchanged. This requires the caller to do a bit more orchestration work for timeouts, but keeps context truer to the "abandon work" intent. This also allows users to force quit _even if_ they are in the middle of a graceful shutdown, rathern than having one behavior mutually exclusive with the other.
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This PR adds support for graceful cancellation and a
GracefulShutdownTimeoutoption for apply and destroy commands.Currently when the context is cancelled a SIGKILL is sent to Terraform. This is the default behaviour of
exec.CommandContext. The SIGKILL forcefully kills the Terraform process and therefore it doesn’t start a graceful shutdown which sometimes ends up with the state lock not being released.The proposed fix is that on context cancellation, a SIGINT is sent so that Terraform starts a graceful shutdown with the hope of releasing the lock and allowing providers to gracefully terminate, and then, after
GracefulShutdownTimeoutif the command hasn’t finished, then a SIGKILL is sent to forcefully terminate the process.When a command is started, the command that is created is run without a context (equivalent to passing
context.Background()), and in a concurrent go routine the cancellation of the parent context is monitored.When the parent context is cancelled, a SIGINT is sent to the command. After
GracefulShutdownTimeoutpasses, if the command hasn't finished, a SIGKILL is sent to the command to forcefully kill it.The
GracefulShutdownTimeoutis also useful so that the caller of tf-exec is able to configure for how long it's willing to wait for the cancellation, which depends on how each provider handles cancellations.Refs