Improve Dockerfile recipe generation (#35187)

- Update default image to Ubuntu 22.04 (previously was still Ubuntu 18.04)
- Optionally use depfiles to install the environment within the container
- Allow extending Dockerfile Jinja2 template
- Allow extending Singularity definition file Jinja2 template
- Deprecate previous options to add extra instructions

1 files changed, 118 insertions, 8 deletions

diff --git a/lib/spack/docs/containers.rst b/lib/spack/docs/containers.rst
index a919db0642..2c097d366c 100644
--- a/lib/spack/docs/containers.rst
+++ b/lib/spack/docs/containers.rst
@@ -444,6 +444,120 @@ attribute:
 The minimum version of Singularity required to build a SIF (Singularity Image Format)
 image from the recipes generated by Spack is ``3.5.3``.
 
+------------------------------
+Extending the Jinja2 Templates
+------------------------------
+
+The Dockerfile and the Singularity definition file that Spack can generate are based on
+a few Jinja2 templates that are rendered according to the environment being containerized.
+Even though Spack allows a great deal of customization by just setting appropriate values for
+the configuration options, sometimes that is not enough.
+
+In those cases, a user can directly extend the template that Spack uses to render the image
+to e.g. set additional environment variables or perform specific operations either before or
+after a given stage of the build. Let's consider as an example the following structure:
+
+.. code-block:: console
+
+   $ tree /opt/environment
+   /opt/environment
+   ├── data
+   │     └── data.csv
+   ├── spack.yaml
+   ├── data
+   └── templates
+       └── container
+           └── CustomDockerfile
+
+containing both the custom template extension and the environment manifest file. To use a custom
+template, the environment must register the directory containing it, and declare its use under the
+``container`` configuration:
+
+.. code-block:: yaml
+   :emphasize-lines: 7-8,12
+
+   spack:
+     specs:
+     - hdf5~mpi
+     concretizer:
+       unify: true
+     config:
+       template_dirs:
+       - /opt/environment/templates
+     container:
+       format: docker
+       depfile: true
+       template: container/CustomDockerfile
+
+The template extension can override two blocks, named ``build_stage`` and ``final_stage``, similarly to
+the example below:
+
+.. code-block::
+   :emphasize-lines: 3,8
+
+   {% extends "container/Dockerfile" %}
+   {% block build_stage %}
+   RUN echo "Start building"
+   {{ super() }}
+   {% endblock %}
+   {% block final_stage %}
+   {{ super() }}
+   COPY data /share/myapp/data
+   {% endblock %}
+
+The recipe that gets generated contains the two extra instruction that we added in our template extension:
+
+.. code-block:: Dockerfile
+   :emphasize-lines: 4,43
+
+   # Build stage with Spack pre-installed and ready to be used
+   FROM spack/ubuntu-jammy:latest as builder
+
+   RUN echo "Start building"
+
+   # What we want to install and how we want to install it
+   # is specified in a manifest file (spack.yaml)
+   RUN mkdir /opt/spack-environment \
+   &&  (echo "spack:" \
+   &&   echo "  specs:" \
+   &&   echo "  - hdf5~mpi" \
+   &&   echo "  concretizer:" \
+   &&   echo "    unify: true" \
+   &&   echo "  config:" \
+   &&   echo "    template_dirs:" \
+   &&   echo "    - /tmp/environment/templates" \
+   &&   echo "    install_tree: /opt/software" \
+   &&   echo "  view: /opt/view") > /opt/spack-environment/spack.yaml
+
+   # Install the software, remove unnecessary deps
+   RUN cd /opt/spack-environment && spack env activate . && spack concretize && spack env depfile -o Makefile && make -j $(nproc) && spack gc -y
+
+   # Strip all the binaries
+   RUN find -L /opt/view/* -type f -exec readlink -f '{}' \; | \
+       xargs file -i | \
+       grep 'charset=binary' | \
+       grep 'x-executable\|x-archive\|x-sharedlib' | \
+       awk -F: '{print $1}' | xargs strip -s
+
+   # Modifications to the environment that are necessary to run
+   RUN cd /opt/spack-environment && \
+       spack env activate --sh -d . >> /etc/profile.d/z10_spack_environment.sh
+
+   # Bare OS image to run the installed executables
+   FROM ubuntu:22.04
+
+   COPY --from=builder /opt/spack-environment /opt/spack-environment
+   COPY --from=builder /opt/software /opt/software
+   COPY --from=builder /opt/._view /opt/._view
+   COPY --from=builder /opt/view /opt/view
+   COPY --from=builder /etc/profile.d/z10_spack_environment.sh /etc/profile.d/z10_spack_environment.sh
+
+   COPY data /share/myapp/data
+
+   ENTRYPOINT ["/bin/bash", "--rcfile", "/etc/profile", "-l", "-c", "$*", "--" ]
+   CMD [ "/bin/bash" ]
+
+
 .. _container_config_options:
 
 -----------------------
@@ -464,6 +578,10 @@ to customize the generation of container recipes:
      - The format of the recipe
      - ``docker`` or ``singularity``
      - Yes
+   * - ``depfile``
+     - Whether to use a depfile for installation, or not
+     - True or False (default)
+     - No
    * - ``images:os``
      - Operating system used as a base for the image
      - See :ref:`containers-supported-os`
@@ -512,14 +630,6 @@ to customize the generation of container recipes:
      - System packages needed at run-time
      - Valid packages for the current OS
      - No
-   * - ``extra_instructions:build``
-     - Extra instructions (e.g. `RUN`, `COPY`, etc.) at the end of the ``build`` stage
-     - Anything understood by the current ``format``
-     - No
-   * - ``extra_instructions:final``
-     - Extra instructions (e.g. `RUN`, `COPY`, etc.) at the end of the ``final`` stage
-     - Anything understood by the current ``format``
-     - No
    * - ``labels``
      - Labels to tag the image
      - Pairs of key-value strings