At Oscar, we wanted to address settings and configuration with a
system that would improve operability, solve the need to change values
deep in the code-base, and consume a variety of sources
(i.e. command-line arguments, environment variables, configuration
oscar.flag is not a module for creating user-friendly
command-line interfaces, but it is a module for faceting a large
code-base for configuration.
Allow any module-level constants and values to be configurable. Any constant value should be a flag, and there should be no penalty for doing so.
Eliminate collisions and reduce clutter by providing namespaces. Each flag should be namespaced to its containing module.
Move flags in code close to the places they are used. Avoid central “config” or “settings” modules. Flags should be consumed in code similar to module constants.
ZK_ENSEMBLE = 'zookeeper-1:2181,zookeeper-2:2181,zookeeper-3:2181' # Becomes this. FLAGS.zk_ensemble = oscar.flag.String('zookeeper ensemble')
Provide clarity from the outside (i.e. command-line). Where a value/flag is used in code should be in the flag name.
# We know immediately that this value is set to a flag that resides in utils.aurora $ ps u | grep 'zookeeper-1' ian 72838 0.0 0.0 2423356 240 s003 R+ 6:31PM 0:00.00 python my_app.py --utils.aurora.zk_ensemble="zookeeper-1:2181"
Allow flags to be set and read from anywhere.
import utils.aurora # Run tests against local zookeeper. utils.aurora.FLAGS.zk_ensemble = 'localhost:2181'
- Provide a set of tools for creating command-line user interfaces. Services and applications are managed through automation (e.g. configuration management).
- Validate flag values. Flag values must marshall, but no further validation is provided.