magpie #14

Supports: trusty xenial bionic eoan focal
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Magpie will check ICMP, DNS, MTU and rx/tx speed between itself and any peer units deployed - deploy more than one magpie unit for meaningful results.

Leadership Layer for Juju Charms

The Leadership layer is for charm-tools and 'charm build', making it easier for layered charms to deal with Juju leadership.

This layer will initialize charms.reactive states, allowing you to write handlers that will be activated by these states. It allows you to completely avoid writing leader-elected and leader-settings-changed hooks. As a simple example, these two handlers are all that is required to make the leader unit generate a password if it is not already set, and have the shared password stored in a file on all units:

import charms.leadership
from import pwgen

def generate_secret():

def store_secret():
    write_file('/etc/foopass', leader_get('admin_password'))


The following states are set appropriately on startup, before any @hook decorated methods are invoked:

  • leadership.is_leader

This state is set when the unit is the leader. The unit will remain the leader for the remainder of the hook, but may not be leader in future hooks.

  • leadership.set.{varname}

This state is set for each leadership setting (ie. the state will be set if the leader has set the foo leadership setting to any value). It will remain set for the remainder of the hook, unless the unit is the leader and calls reactive.leadership.leader_set() and resets the value to None.

  • leadership.changed.{varname}

This state is set for each leadership setting that has changed since the last hook. It will remain set for the remainder of the hook. It will not be set in the next hook, unless the leader has changed the leadership setting yet again.

  • leadership.changed

One or more leadership settings has changed since the last hook. This state will remain set for the remainder of the hook. It will not be set in the next hook, unless the leader has made further changes.


The charms.leadership module exposes the leader_set() and leader_get() methods, which match the methods found in the charmhelpers.core.hookenv module. reactive.leadership.leader_set() should be used instead of the charmhelpers function to ensure that the reactive state is updated when the leadership settings are. If you do not do this, then you risk handlers waiting on these states to not be run on the leader (because when the leader changes settings, it triggers leader-settings-changed hooks on the follower units but no hooks on itself).


This layer is maintained on Launchpad by Stuart Bishop (

Code is available using git at git+ssh://

Bug reports can be made at

Queries and comments can be made on the Juju mailing list, Juju IRC channels, or at


(string) Comma separated list of expected bonds or AUTO to check all available bonds.
(boolean) Check if peers are resolveble
(boolean) Execute iperf network performance test
(boolean) Check if local hostname is resolvable
(boolean) Check LLDP port description to match hostname
(string) Use unit default DNS server
(int) Timeout in seconds per DNS query try
(int) Number of DNS resolution attempts per query
(int) Time in seconds to run iperf to test the transfer speed. Larger value can be set to mitigate the impact of CPU power saving features especially on faster links such as 50G.
(int) Minimum transfer speed in mbit/s required to pass the test. 0 disables.
(int) Timeout in seconds per ICMP request
(int) Number of ICMP packets per ping
(int) Desired MTU for all nodes - block if the unit MTU is different (accounting for encapsulation). 0 disables.
(string) Repository to add to unit before installing any dependencies. May be one of the following: distro (default) ppa:somecustom/ppa (PPA name must include UCA OpenStack Release name) deb url sources entry|key id or a supported Ubuntu Cloud Archive pocket.
(boolean) Enable this if you intend to consume this layer - supresses status messages
(boolean) Enable LLDP agent and collect data