JENKINS-66373: idle timeout should not fight with min spare instances setting #945
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The problem
Currently if you use the "Minimum number of spare instances" setting as well as "Idle termination time", then there is a constant battle going on between:
MinimumInstanceChecker.checkForMinimumInstances
provisioning new agents to try and maintain the minimum number of spare instances as configuredThis means that the spare instances are repeatedly killed & recreated as described on https://issues.jenkins.io/browse/JENKINS-66373 which is wasteful and means that, some percentage of the time, there are never enough spare instances because they are being booted (again).
Solution
This PR makes a simple change to the idle termination logic so that it takes account of "Minimum number of spare instances" in the same way that it already accounts for the main "Minimum number of instances" setting.
Testing done
None yet -
EC2RetentionStrategyTest.java
seems like the right place to add a test case for this specific scenario.Right now I've got very limited time and wanted to at least get the proposed fix up for discussion to start with.
Submitter checklist