add 'no-pip-install' recipe

custom-recipes/recipes/no-pip-install/EXTERNALLY-MANAGED

@@ -0,0 +1,9 @@
+[externally-managed]
+Error=This is a pure conda environment, packages should not be installed into it directly via pip.
+
+  If you are a user see this page for more information on using our environments: https://european-xfel.github.io/environments/environments/
+
+  For DA staff see the environment maintenance documentation:
+
+    - Environment maintenance: https://european-xfel.github.io/environments/maintenance/environments/
+    - Recipe creation: https://european-xfel.github.io/environments/maintenance/recipes/

custom-recipes/recipes/no-pip-install/README.md

@@ -0,0 +1,5 @@
+# No Pip Install
+
+This 'package' use [PEP 668](https://peps.python.org/pep-0668/) to mark a conda environment it is installed into as 'externally managed', disallowing `pip install` commands from being run in the environment.
+
+It should be included in our per-cycle conda environments to prevent the environments from becoming difficult to maintain and track due to changes made by pip.

custom-recipes/recipes/no-pip-install/recipe.yaml

@@ -0,0 +1,32 @@
+context:
+  name: no-pip-install
+  version: 0.1.0
+
+package:
+  name: '{{ name|lower }}'
+  version: '{{ version }}'
+
+source:
+  path: .
+
+build:
+  script: "cp ./EXTERNALLY-MANAGED ${SP_DIR}/../."
+
+requirements:
+  host:
+    - python >=3
+  run:
+    - python >=3
+    - pip >=23.0
+
+test:
+  commands:
+    - cat $STDLIB_DIR/EXTERNALLY-MANAGED
+
+about:
+  license: GPL-3.0
+
+extra:
+  recipe-maintainers:
+    - RobertRosca
+

docs/maintenance/environments.md

@@ -8,12 +8,20 @@ Each environment directory will have a few files:
 
 - `0-desy-pinned.yml` - environment file with a few packages that we should keep in sync with DESY, e.g. if we have a different version of `ipympl` (interactive plotting backend for matplotlib) to the one in the DESY Conda environment that is running Max-JHub then there may be problems with interactive plotting due to incompatibilities.
 - `1-base.yml` - Conda environment file containing packages which are available on a Conda channel
-- `2-custom.yml` - optional Conda environment file containing packages built from custom recipes (see [Recipes](./recipes.md))
+- `2-custom.yml` - optional Conda environment file containing packages built from custom recipes (see [Custom Recipes](./recipes.md))
 - `environment.yml` - file generated by merging the three files from above into one
 - `environment.lock.yml` - the output of `conda env export`, contains the versions of all packages installed in the environment
 
 Environments exist in an installation of Conda, setting up a new Conda installation is very rarely required and is covered in the [Instances](./instances.md) section.
 
+!!! warning
+
+    The cycle environments are **pure conda environments**, you should not run `pip install` commands to add packages to them. Any package added to the per-cycle environments should be a conda package.
+
+    If you need to add a package which is not available on a Conda channel then you should create a recipe for it as described in [Custom Recipes](./recipes.md).
+
+    A special `no-pip-install` package is installed into the cycle environments to prevent direct package installation via pip.
+
 ## Creating a New Specification
 
 The first step to creating a new environment is activating an installation, this can be done with `module load exfel mambaforge`. Loading this module will initialise the Conda instance into the `base` environment which provides useful tools for environment management.