Allow multiple worker processes with cluster module #1705
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Joxit
approved these changes
Oct 15, 2025
missinglink
reviewed
Oct 16, 2025
This adds the ability for the API to use multiple worker processes with Node.js's builtin [`cluster`](https://nodejs.org/api/cluster.html) module. Historically, I've been opposed to adding this functionality, preferring that Pelias users manage parallelism on their own such as with Kubernetes or something else. But there are enough use cases where that sort of orchestration isn't worth the complexity, and you want more than one CPU's worth of API requests. This implementation is essentially lifted from the one in Placeholder, with mostly cosmetic changes only. The biggest difference is the default. For backwards compatibility, without specifing the new `CPUS` environment variable, the API will _not_ use the cluster module and operate as a single process just like before. _With_ the `CPUS` variable set to a number, that many worker processes will be launched, up to the number of CPUs detected on the machine.
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This adds the ability for the API to use multiple worker processes with Node.js's builtin
clustermodule.Historically, I've been opposed to adding this functionality, preferring that Pelias users manage parallelism on their own such as with Kubernetes or something else.
But there are enough use cases where that sort of orchestration isn't worth the complexity, and you want more than one CPU's worth of API requests.
This implementation is essentially lifted from the one in Placeholder, with mostly cosmetic changes only.
The biggest difference is the default. For backwards compatibility, without specifing the new
CPUSenvironment variable, the API will not use the cluster module and operate as a single process just like before.With the
CPUSvariable set to a number, that many worker processes will be launched, up to the number of CPUs detected on the machine.