Currently the autoscaling configuration of `docker+machine` executor is simple and allows to define two kinds of settings: for normal and _OffPeak_ periods. It may look for example like that: ```toml [docker.machine] (...) MaxBuilds = 1 IdleCount = 100 IdleTime = 3600 OffPeakPeriods = ["* * * * * sat,sun *"] OffPeakTimezone = "UTC" OffPeakIdleCount = 70 ``` The configuration defines that normally we should have 100 machines in `idle` state, except for whole Saturdays and Sundays, when it should have only 10 `idle` machines. While this works well, we've found that a possibility to define more custom settings for different timings is needed. The above example is taken from GitLab.com Shared Runners config. We want to have a little less `idle` machines at weekends, when the load is smaller. However while working on resolving a _4am spikes problem_, we'd decide that we want to define specific settings for around the 4am hour each day **apart of existing configuration**. The proposal is to create new configuration syntax: ```toml [docker.machine] (...) MaxBuilds = 1 [[docker.machine.autoscaling]] Periods = ["* * * * * * *"] # Maybe use it as default, so for the default cases it could be left undefined (less work to do)? Timezone = "UTC" IdleCount = 100 IdleTime = 3600 [[docker.machine.autoscaling]] Periods = ["* * * * * sat,sun *"] # The weekends, configured above with the 'OffPeak' settings Timezone = "UTC" IdleCount = 70 IdleTime = 3600 [[docker.machine.autoscaling]] Periods = ["* * 3-4 * * * *"] # The 'around 4am' case Timezone = "UTC" IdleCount = 1000 IdleTime = 3600 ``` In this case Runner would iterate over all `docker.machine.autoscaling` definitions searching for **the last one that matches current time**. And then it would apply the configuration values. So looking on the above example, normally we would have 100 `idle` machines, at weekends it would be reduced to 70, and at any day (no matter if it's a weekend or not) at 3-4am UTC it would be increased to 1000. While implementing this we should also deprecate the old configuration values, since these would allow to get the same result **and something more**. When the old configuration only would be used, we should log then a deprecation notice. If both would be used - we should log that the old one is disabled (and repeat the deprecation notice). We should also consider if we want to require at least one `docker.machine.autoscaling` entry with explicit configuration, or do we don't care and just default to `0` for `IdleCount` and `IdleTime` values. This would be the easiest approach and would also resolve the case of a configuration that doesn't cover some specific time period.