A workflow that takes seconds on my local machine takes 15 minutes or more on the GitHub CI because the whole world starting from the compiler is downloaded and compiled from sources. This is very different for a C project because the C compiler and many libraries come pre-installed or are installed…

You can supply a Dockerfile that uses a fixed version of the opam-repository to allow image reuse. See, e.g. docker-base-images/Dockerfile at master · ocurrent/docker-base-images · GitHub

I’ve been wondering the same but without really taking the time to fix it properly. It feels like, ideally, the ocaml-setup action should allow us to load docker images that: have an exact OCaml version have an exact opam-repo hash (for better caching, reproducibility, etc) obviously this would …

[image] c-cube: It feels like, ideally, the ocaml-setup action should allow us to load docker images that: have an exact OCaml version have an exact opam-repo hash (for better caching, reproducibility, etc) Both of these have been autobuilt and published on the OCaml Docker Hub since 2015; …

Docker images certainly help reducing CI time, but still take significant time to load. The fastest Github CI runs I’ve seen with CompCert (a mixed Rocq/OCaml project) were obtained by using binary, precompiled Homebrew packages on macOS.

I always create my docker images using GitHub - mjambon/ocaml-layer: Make your own OCaml base image for fast CI jobs · GitHub I tried to touch prebuilt images (from ocurrent or something else) and never succeeded. Either user name by default is weird and it is not obvious where to put stuff, or som…

Are you suggesting that people should do their CI inside of a dockerfile (with a FROM <exact dockerhub image> at the start), then? I’m not opposed to it at all but I thought setup-ocaml (which doesn’t do that, does it?) was the “official” way to do CI for OCaml projects. I’ve been annoyed by the se…

Sorry in advance for theorizing :slight_smile: Is the problem that we’re building everything from source, or is it that we’re not caching the results across CI runs? For example, 4ward is a complex, multi language project (mostly Kotlin and C++; no OCaml) pulling in lots of heavy dependencies, yet…

[image] c-cube: Are you suggesting that people should do their CI inside of a dockerfile (with a FROM <exact dockerhub image> at the start), then? I’m not opposed to it at all but I thought setup-ocaml (which doesn’t do that, does it?) was the “official” way to do CI for OCaml projects. I’m s…

I started using Nix in CI and now the CI time is between 2 to 7 minutes, whereas before it used to be 25 to 30+ minutes.

To add to the landscape of approaches, I believe it is worth mentioning the setup-dune project by Tarides. Its approach is to access a pre-compiled dune binary, and then use dune pkg to download the dependencies and compile the project The goal is then to use dune-cache features combined with GH ca…

GitHub CI execution times for OCaml projects

Ecosystem

jbeckford September 19, 2026, 4:31pm 20

I posted an alternative solution: Dk builds with relocatable OCaml

Like Docker but unlike GitHub Actions cache-based solutions, the alternative can also speedup local development.

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GitHub CI execution times for OCaml projects

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