Policy packages are separate Python packages that can be used to add experiment-specific customisations to Rucio. They typically customise Rucio’s handling of permissions and schema as well as optionally adding their own algorithms for lfn to pfn conversion and surl construction.
Policy packages may be installed from a Python package repository such as PyPi or they may simply be installed in a local directory. In the latter case this directory will need to be added to the Rucio server’s PYTHONPATH environment variable.
The name of the policy package in use is specified by the package value in the [policy] section of the Rucio configuration file. If no package is specified, a built in generic policy will be used. If a package is specified but cannot be loaded, Rucio will exit with an error.
Creating a policy package¶
The structure of a policy package is very simple. It contains the following:
- a permission.py module implementing permission customisations.
- a schema.py module implementing schema customisations.
- an optional __init__.py file that registers lfn to pfn and surl construction algorithms when the package is loaded. It should also contain a SUPPORTED_VERSION field.
The easiest way to create the permission.py and schema.py modules is to modify the generic versions from the Rucio codebase. These can be found in lib/rucio/core/permission/generic.py and lib/rucio/common/schema/generic.py respectively.
In the has_permission function you may wish to default to the generic permission checks if your experiment does not need specific functionality for a particular action, or so that new actions added to Rucio will work without your policy package having to be updated. This fallback can be implemented with code similar to the following:
import rucio.core.permission.generic if action not in perm: return rucio.core.permission.generic.has_permission(issuer, action, kwargs)
__init__.py should include a SUPPORTED_VERSION field indicating the version of Rucio that your package was developed against. This may be checked by Rucio in the event that the policy package interface changes in the future. Example:
SUPPORTED_VERSION = "1.20.7"
Custom surl construction algorithms can be registered in __init__.py:
from rucio.common.utils import register_surl_algorithm register_surl_algorithm(construct_surl_special, 'special')
So can custom lfn to pfn algorithms:
from rucio.rse.protocols.protocol import RSEDeterministicTranslation RSEDeterministicTranslation.register(lfn2pfn_special, 'special')