Colmena is built from the ground up to support parallel deployments. Evaluation, build, and deployment of node configurations can happen at the same time.


The parallelism of Colmena can be controlled through two flags:

--limit <number>

Number of hosts to deploy at once in the final step (pushing closures and activating new profiles). The default value is 10.

--eval-node-limit <number>

By default, Colmena will automatically determine the maximum number of nodes to evaluate at the same time according to available RAM. This flag allows you to set the limit to a predetermined value.

Parallel Evaluation (Experimental)

By default, Colmena evaluates nodes in batches according to available RAM using Nix's built-in single-threaded evaluator. Experimental support is available for using nix-eval-jobs as the evaluator.

When nix-eval-jobs is enabled via --evaluator streaming, evaluation is parallelized with deployment processes kicked off as individual nodes finish evaluating.