See also: Unit
This document demonstrates various operations that you can perform on a unit.
Units are also relevant when adding storage or scaling an application. See How to manage storage and How to manage applications.
Add a unit
To add a unit, use the add-unit command followed by the application name:
This is only true for machine deployments. For Kubernetes, see How to control the number of units.
juju add-unit mysql
By using various command options, you can also specify the number of units, the model, the kind of storage, the target machine (e.g., if you want to collocate multiple units of the same or of different applications on the same machine – though watch out for potentials configuration clashes!), etc.
See more:
juju add-unit
To add a unit in python-libjuju client, you simply call add_unit() on your Application object, as follows:
my_app.add_unit(count=3)
See more:
Application (module), Application.add_unit(), Application.scale()
Control the number of units
The procedure depends on whether you are on machines or rather Kubernetes.
Machines. To control the number of an application’s units in a machine deployment, add or remove units in the amount required to obtain the desired number.
See more: How to add a unit, How to remove a unit
Kubernetes. To control the number of an application’s units in a Kubernetes deployment, run the scale-application command followed by the number of desired units (which can be both higher and lower than the current number).
juju scale-application mediawiki 3
See more:
juju scale-application
To control the number of units of an application, in its resource definition specify a units attribute. For example, below we set it to 3.
resource "juju_application" "this" {
model = juju_model.development.name
charm {
name = "hello-kubecon"
}
units = 3
}
See more:
juju_application(resource)
To control the number of units of an application in python-libjuju client, you can use the Application.add_unit() and Application.destroy_units() methods, or the Application.scale() method, depending on whether you’re working on a CAAS system (e.g. Kubernetes), or an IAAS system (e.g. lxd).
If you’re on an IAAS system (machine applications):
u = my_app.add_unit()
my_app.destroy_units(u.name) # Note that the argument is the name of the unit
# You may give multiple unit names to destroy at once
my_app.destroy_units(u1.name, u2.name)
If you’re on a CAAS sytem (k8s applications):
my_app.scale(4)
See more:
Application (module), Application.add_unit(), Application.scale(), Application.destroy_units()
Show details about a unit
To see more details about a unit, use the show-unit command followed by the unit name:
juju show-unit mysql/0
By using various options you can also choose to get just a subset of the output, a different output format, etc.
See more:
juju show-unit
Too see details about a unit in python-libjuju client, you can use various fields and methods of a Unit object. For example, to get the public_address of a unit:
my_unit.get_public_address()
Or, to see if the unit is a leader:
my_unit.is_leader_from_status()
See more:
Unit(module), Unit (methods), Unit.get_public_address(), Unit.is_leader_from_status()
List a unit’s resources
To see the resources for a unit, use the resources command followed by the unit name. For example:
juju resources mysql/0
See more:
juju resources
The python-libjuju client does not support this. Please use the juju client.
Related: Application.get_resources()
Show the status of a unit
To see the status of a unit, use the status command:
juju status
This will show information about the model, along with its machines, applications and units. For example:
Model Controller Cloud/Region Version SLA Timestamp
tutorial-model tutorial-controller microk8s/localhost 2.9.34 unsupported 12:10:16+02:00
App Version Status Scale Charm Channel Rev Address Exposed Message
mattermost-k8s .../mattermost:v6.6.0-20.04... active 1 mattermost-k8s stable 21 10.152.183.185 no
postgresql-k8s .../postgresql@ed0e37f active 1 postgresql-k8s stable 4 no Pod configured
Unit Workload Agent Address Ports Message
mattermost-k8s/0* active idle 10.1.179.151 8065/TCP
postgresql-k8s/0* active idle 10.1.179.149 5432/TCP Pod configured
See more:
juju status, Unit status
To get the status of a unit on pylibjuju-client, you can use various (dynamically updated) status fields defined on a Unit object, such as:
workload_st = my_unit.workload_status
agent_st = my_unit.agent_status
See more: Unit status,
Unit(module), Unit (methods), Unit.workload_status (field), Unit.agent_status (field)
Set the meter status on a unit
To set the meter status on a unit, use the set-meter-status command followed by the unit name. For example:
juju set-meter-status myapp/0
See more:
juju set-meter-status
The python-libjuju client does not support this. Please use the juju client.
Mark unit errors as resolved
To mark unit errors as resolved, use the resolved command followed by the unit name or a list of space-separated unit names. For example:
juju resolved myapp/0
See more:
juju resolved
To mark unit errors as resolved in the python-libjuju client, you can call the resolved() method on a Unit object:
my_unit.resolved()
See more:
Unit.resolved()
Remove a unit
To remove individual units instead of the entire application (i.e. all the units), use the remove-unit command followed by the unit name. For example, the code below removes unit 2 of the PostgreSQL charm. For example:
While this can be used for both machine and Kubernetes deployments, unless you care about which unit you’re removing specifically, in Kubernetes you may also just run juju scale-application <n>, where n is less than the current number of units. See How to control the number of units.
juju remove-unit postgresql/2
In the case that the removed unit is the only one running, the corresponding machine will also be removed, unless any of the following is true for that machine:
- it was created with
juju add-machine - it is not being used as the only controller
- it is not hosting Juju-managed containers (KVM guests or LXD containers)
It is also possible to remove multiple units at a time by passing instead a space-separated list of unit names:
juju remove-unit mediawiki/1 mediawiki/3 mediawiki/5 mysql/2
To also destroy the storage attached to the units, add the --destroy-storage option.
As a last resort, use the --force option (in v.2.6.1).
See more:
juju remove-unit, Removing things reference
To remove individual units on python-libjuju client, simply use the Application.destroy_units() method:
my_app.destroy_units(u.name) # Note that the argument is the name of the unit
# You may give multiple unit names to destroy at once
my_app.destroy_units(u1.name, u2.name)
See more:
Application (module), Application.destroy_units()
Contributors: @cderici, @hmlanigan, @skourta, @tmihoc