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Running Molecule processes in parallel mode


This functionality should be considered experimental. It is part of ongoing work towards enabling parallelizable functionality across all moving parts in the execution of the Molecule feature set.


Only the following sequences support parallelizable functionality:

  • check_sequence: molecule check --parallel
  • destroy_sequence: molecule destroy --parallel
  • test_sequence: molecule test --parallel

It is currently only available for use with the Docker driver.

When Molecule receives the --parallel flag it will generate a UUID for the duration of the testing sequence and will use that unique identifier to cache the run-time state for that process. The parallel Molecule processes cached state and created instances will therefore not interfere with each other.

Molecule uses a new and separate caching folder for this in the $HOME/.cache/molecule_parallel location. Molecule exposes a new environment variable MOLECULE_PARALLEL which can enable this functionality.

It is possible to run Molecule processes in parallel using another tool to orchestrate the parallelization (such as GNU Parallel or Pytest). If you do so, make sure Molecule knows it is running in parallel mode by specifying the --parallel flag to your command(s) to avoid concurrency issues.