[Logs] Fix a race condition in CloudWatch Agent startup that could cause nodes bootstrap failures #2993
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… `/etc/parallelcluster/amazon-cloudwatch-agent/amazon-cloudwatch-agent.json`. This is to prevent a race condition in the way we start the CW agent, that may lead to undesired deletion of the config file and eventually the node bootstrap failure caused by CW agent failing to start.
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Description of changes
Fix a race condition in CloudWatch Agent startup that could cause nodes bootstrap failures.
To do that we simply need to move the staging configuration created by pcluster from
/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.jsonto/etc/parallelcluster/amazon-cloudwatch-agent/amazon-cloudwatch-agent.json.Why moving that file solves the race condition?
We start the CloudWatch Agent by using
amazon-cloudwatch-agent-ctl, providing as input the configuration file we author; see code. In particular we execute two times that command in two different modes, as safety net. However, that command assumes to have full control over directories in/opt/aws/amazon-cloudwatch-agent/etc/. In particular, there is a path in the code that may trigger the removal of files in that directory, thus removing the configuration file. So when the first command fails and the second one is execute, the config file provided as input may have been deleted by the first execution.Moving the config file out of
/opt/aws/amazon-cloudwatch-agent/etc/is the mitigation suggested by the CloudWatch team itself.Tests
test_cloudwatch_loggingBy submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.