Merge pull request #653 from boegel/spack-poc

add blog post on PoC with using Spack on top of EESSI

Author: ocaisa

docs/blog/.authors.yml

@@ -79,3 +79,8 @@ authors:
     description: CECAM-HQ (EPFL)
     avatar: https://avatars.githubusercontent.com/u/34096612?v=4
     slug: https://github.com/Crivella
+  lorisercole:
+    name: Loris Ercole
+    description: CECAM-HQ (EPFL)
+    avatar: https://avatars.githubusercontent.com/u/30901257?v=4
+    slug: https://github.com/lorisercole

docs/blog/posts/2026/01/Spack-on-top-of-EESSI-PoC.md

@@ -0,0 +1,94 @@
+---
+authors: [lorisercole, ocaisa, boegel]
+date: 2026-01-09
+slug: Spack-on-top-of-EESSI-PoC
+---
+
+# Using Spack on top of EESSI: A Proof of Concept
+
+<figure markdown="span">
+![Spack + EESSI](spack-plus-eessi.webp){width=75%}
+</figure>
+
+EESSI provides a rich set of software installations, which were built and installed using
+[EasyBuild](https://easybuild.io).
+
+Can we convince [Spack](https://spack.io) to reuse software installed in EESSI,
+and by doing so make EESSI more attractive to those of you who prefer using Spack over EasyBuild?
+
+Several people have expressed interest in exposing the software installations provided by EESSI
+to Spack, so they can be used as dependencies when building and installing software with Spack.
+
+Recently, we have explored how this could be achieved through a proof-of-concept with [QuantumESPRESSO](https://www.quantum-espresso.org/).
+
+The goal here is to build and install only QuantumESPRESSO with Spack,
+and leveraging software installations from EESSI for all required dependencies, including the compiler and libraries for MPI, BLAS/LAPACK, FFTW, etc.
+
+<!-- more -->
+
+### Step 1: A Spack database for EESSI
+
+To get started, we created an external *Spack database* using the [`spack.database.Database` class](https://spack.readthedocs.io/en/latest/spack.html#module-spack.database)
+that Spack provides, which exposes software installed in EESSI to Spack.
+
+This was done through a Python script, and only for a small set of hand-picked software
+installations: those that are build or runtime dependencies of QuantumESPRESSO.
+
+Using `spack find`, we can check whether Spack is aware of these installations:
+
+![Spack database for software installations included in EESSI](spack-eessi-20251106-001.webp)
+
+Looks good so far...
+
+
+### Step 2: Checking required dependencies for QuantumESPRESSO
+
+Spack being aware of software installed in EESSI is not sufficient though.
+We need to make sure those installations are also actually *used* by Spack to resolve required dependencies.
+
+For this, we need to provide the necessary metadata for those installations,
+including which [*variants*](https://spack.readthedocs.io/en/latest/packaging_guide_creation.html#variants) they provide.
+When done correctly, we can see that all required dependencies are indeed resolved using `spack spec`:
+
+![Checking required dependencies with `spack spec`](spack-eessi-20251106-002.webp)
+
+Here, we use `@7.4.1` to specify the QuantumESPRESSO version we want to install,
+and `~mpi` to ensure that the QuantumESPRESSO installation will have MPI support.
+
+
+### Step 3: Installing QuantumESPRESSO with Spack
+
+The real test consist of actually trying to build and install QuantumESPRESSO using Spack,
+by running `spack install quantum-espresso`:
+
+![Installing QuantumESPRESSO with `spack install`](spack-eessi-20251106-003.webp)
+
+That worked like charm!
+
+
+### Step 4: Running QuantumESPRESSO
+
+Finally, we try to actually *run* QuantumESPRESSO as it was installed with Spack.
+
+We set up the environment with `spack load quantum-espresso`, and feed an input file into the main command `pw.x`:
+
+![Running the `pw.x` binary](spack-eessi-20251106-004.webp)
+
+This was just a simple single-core test, but it does seem to work as expected!
+
+When we inspect the `pw.x` binary a bit more closely, we can see that it (only) links to libraries provided by EESSI:
+
+![Inspecting the list of libraries that `pw.x` binary links to](spack-eessi-20251106-005.webp)
+
+
+It's clear that more work needs to be done to further validate the installation and check its performance,
+but this is a nice first step...
+
+
+### More information & updates
+
+This work is being done in collaboration with member of the Spack development team,
+including Todd Gamblin and Massimiliano Culpo.
+
+For updates, check the [dedicated support issue](https://gitlab.com/eessi/support/-/issues/170)
+that was opened on using Spack on top of EESSI, or stay tuned for future blog posts!