Generating a Persistent or Transient Configuration Change in Python Commit Scripts
Junos OS commit scripts enforce custom configuration rules and can automatically change the configuration when it does not comply with your custom configuration rules. To generate a persistent or transient change using Python commit scripts:
- At the start of the script, include the Python boilerplate
from Required Boilerplate for Commit Scripts, which is reproduced here for convenience:
from junos import Junos_Configuration import jcs if __name__ == '__main__': # insert your code here
- Include one or more programming instructions that test
for your custom configuration rules.
For example, the following code selects each SONET/SDH interface that does not have the MPLS protocol family enabled:
# Get configuration root object root = Junos_Configuration for element in root.xpath("./interfaces/ \ interface[starts-with(name,'so-')]"): if element.find('unit/family/mpls') is None: - Create an XML string that instructs Junos OS how to modify
the configuration.
This example enables the MPLS protocol family for the selected interfaces.
if_name = element.find('name').text unit_name = element.find('unit/name').text change_xml = """ <interfaces> <interface> <name>{0}</name> <unit> <name>{1}</name> <family> <mpls> </mpls> </family> </unit> </interface> </interfaces> """.format(if_name, unit_name).strip() - Include any additional required or optional code. This
example generates a warning message that is displayed on the CLI when
the commit script updates a SONET/SDH interface.
jcs.emit_warning("Adding 'family mpls' to SONET interface: " + if_name) - To generate the persistent or transient change, call the
jcs.emit_changemethod, and specify the type of change, either 'change' or 'transient-change', in the argument list.jcs.emit_change(change_xml, "change", "xml")
- Save the script with a meaningful name.
- Copy the script to either the
/var/db/scripts/commitdirectory on the device hard disk or the/config/scripts/commitdirectory on the flash drive.Note Unsigned Python scripts must be owned by either root or a user in the Junos OS super-user login class, and only the file owner can have write permission for the file.
- Enable the script by configuring the file filename statement at the [edit system scripts
commit] hierarchy level.[edit]user@host# set system scripts commit file filename
- If the script generates any transient changes, configure
the allow-transients statement.[edit]user@host# set system scripts commit allow-transients
- Enable the execution of unsigned Python scripts on the
device.[edit system scripts]user@host# set language (python | python3)
- Issue the commit command to commit the configuration.user@host# commit
The resulting script searches for SONET/SDH interfaces that do not have the MPLS protocol family enabled, adds the family mpls statement at the [edit interfaces so-fpc/pic/port unit logical-unit-number] hierarchy level as a persistent change, and emits a warning message stating that the configuration has been changed.
from junos import Junos_Configuration
import jcs
def main():
# Get configuration root object
root = Junos_Configuration
for element in root.xpath("./interfaces/ \
interface[starts-with(name,'so-')]"):
if element.find('unit/family/mpls') is None:
if_name = element.find('name').text
unit_name = element.find('unit/name').text
change_xml = """
<interfaces>
<interface>
<name>{0}</name>
<unit>
<name>{1}</name>
<family>
<mpls>
</mpls>
</family>
</unit>
</interface>
</interfaces>
""".format(if_name, unit_name).strip()
jcs.emit_change(change_xml, "change", "xml")
jcs.emit_warning("Adding 'family mpls' to SONET interface: " + if_name)
if __name__ == '__main__':
main()
If all enabled commit scripts run without errors, any persistent changes are loaded into the candidate configuration, and any transient changes are loaded into the checkout configuration, but not to the candidate configuration. The commit process then continues by validating the configuration and propagating changes to the affected processes on the device.
To display the configuration with both persistent and transient changes applied, issue the show | display commit-scripts configuration mode command.
To display the configuration with only persistent changes applied, issue the show | display commit-scripts no-transients configuration mode command.
Persistent and transient changes are loaded into the configuration
in the same manner that the load replace configuration
mode command loads an incoming configuration. When generating a persistent
or transient change, adding the replace="replace" attribute to a configuration element produces the same behavior
as a replace: tag in a load replace operation. Both persistent and transient changes are loaded into
the configuration with the load replace behavior. However,
persistent changes are loaded into the candidate configuration, and
transient changes are loaded into the checkout configuration.