reclass can read some of its configuration from a file. The file is a YAML-file and simply defines key-value pairs.
The configuration file can be used to set defaults for all the options that are otherwise configurable via the command-line interface, so please use the --help output of reclass (or the manual page) for reference. The command-line option --nodes-uri corresponds to the key nodes_uri in the configuration file. For example:
storage_type: yaml_fs
pretty_print: True
output: json
inventory_base_uri: /etc/reclass
nodes_uri: ../nodes
reclass first looks in the current directory for the file called reclass-config.yml (see reclass/defaults.py) and if no such file is found, it looks in $HOME, then in /etc/reclass, and then “next to” the reclass script itself, i.e. if the script is symlinked to /srv/provisioning/reclass, then the the script will try to access /srv/provisioning/reclass-config.yml.
Note that yaml_fs is currently the only supported storage_type, and it’s the default if you don’t set it.
Adapters may implement their own lookup logic, of course, so make sure to read their documentation (for Salt, for Ansible, and for Puppet).