`spack containerize` generates containers from envs (#14202)

This PR adds a new command to Spack:
```console
$ spack containerize -h
usage: spack containerize [-h] [--config CONFIG]

creates recipes to build images for different container runtimes

optional arguments:
  -h, --help       show this help message and exit
  --config CONFIG  configuration for the container recipe that will be generated
```
which takes an environment with an additional `container` section:
```yaml
spack:
  specs:
  - gromacs build_type=Release 
  - mpich
  - fftw precision=float
  packages:
    all:
      target: [broadwell]

  container:
    # Select the format of the recipe e.g. docker,
    # singularity or anything else that is currently supported
    format: docker
    
    # Select from a valid list of images
    base:
      image: "ubuntu:18.04"
      spack: prerelease

    # Additional system packages that are needed at runtime
    os_packages:
    - libgomp1
```
and turns it into a `Dockerfile` or a Singularity definition file, for instance:
```Dockerfile
# Build stage with Spack pre-installed and ready to be used
FROM spack/ubuntu-bionic:prerelease as builder

# 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 "  - gromacs build_type=Release" \
&&   echo "  - mpich" \
&&   echo "  - fftw precision=float" \
&&   echo "  packages:" \
&&   echo "    all:" \
&&   echo "      target:" \
&&   echo "      - broadwell" \
&&   echo "  config:" \
&&   echo "    install_tree: /opt/software" \
&&   echo "  concretization: together" \
&&   echo "  view: /opt/view") > /opt/spack-environment/spack.yaml

# Install the software, remove unecessary deps and strip executables
RUN cd /opt/spack-environment && spack install && spack autoremove -y
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:18.04

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 /etc/profile.d/z10_spack_environment.sh /etc/profile.d/z10_spack_environment.sh

RUN apt-get -yqq update && apt-get -yqq upgrade                                   \
 && apt-get -yqq install libgomp1 \
 && rm -rf /var/lib/apt/lists/*

ENTRYPOINT ["/bin/bash", "--rcfile", "/etc/profile", "-l"]
```

1 files changed, 25 insertions, 0 deletions

diff --git a/lib/spack/spack/cmd/containerize.py b/lib/spack/spack/cmd/containerize.py
new file mode 100644
index 0000000000..cc2c001560
--- /dev/null
+++ b/lib/spack/spack/cmd/containerize.py
@@ -0,0 +1,25 @@
+# Copyright 2013-2020 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import os
+import os.path
+import spack.container
+
+description = ("creates recipes to build images for different"
+               " container runtimes")
+section = "container"
+level = "long"
+
+
+def containerize(parser, args):
+    config_dir = args.env_dir or os.getcwd()
+    config_file = os.path.abspath(os.path.join(config_dir, 'spack.yaml'))
+    if not os.path.exists(config_file):
+        msg = 'file not found: {0}'
+        raise ValueError(msg.format(config_file))
+
+    config = spack.container.validate(config_file)
+
+    recipe = spack.container.recipe(config)
+    print(recipe)