Basic client usage - tutorial

The goal of this tutorial is to give new Juju operators a solid introduction to the command line client. In so doing, several important concepts are introduced. It also discusses the use of command prefixes and aliases. Further reading suggestions are included at the end.


The following prerequisites are assumed as a starting point for this tutorial:

  • You're using Ubuntu 18.04 LTS (Bionic).
  • Juju (stable snap channel) is installed. See the Installing Juju page.
  • You have chosen a backing cloud and have created a controller for it. Refer to the Clouds page to get started with a cloud and controller.

This guide uses LXD (v.3.9) as a backing cloud due to its accessibility and low resource usage. Choose a local LXD cloud if you're not sure what to use (see Using LXD with Juju).

Command prefixes and aliases

As you gain more experience with the client, you will discover a common set of command prefixes: add-, create-, destroy-, get-, list-, remove-, set-, and show-.

Generally their meanings are self-evident but some require explanation. A good example of this are the destroy- and remove- prefixes, such as in the commands destroy-model and remove-user. These two prefixes differ in terms of severity. Basically, destroy- indicates a destructive action that is difficult to reverse whereas remove- does not.

There is a kill- prefix but it is reserved for a single command: kill-controller. The latter differs from destroy-controller in that it has the ability to terminate the controller machine directly via the cloud provider, without cleaning up any machines that may be running in workload models.

The list- prefix can often be omitted as there is usually a corresponding command alias available. For instance, clouds can be used instead of list-clouds. The list of aliases can be obtained in this way:

juju help commands | grep Alias

The show- prefix is used to drill down into an object to reveal details. It is akin to the verb "describe".

Fundamental commands

Juju makes available to the operator a wide variety of commands. In this section, we'll cover the basic ones.

Listing initial information

List the controller:

juju controllers

This will return a list of all the controllers known to your Juju client. Below, we have a controller named 'lxd':

Controller  Model    User   Access     Cloud/Region         Models  Machines    HA  Version
lxd*        default  admin  superuser  localhost/localhost       2         1  none  2.5.0

A newly-created controller has two models: The 'controller' model, which should be used only for internal Juju management, and a 'default' model, which is ready for actual use.

Confirm the above by listing all the models in the currently active controller:

juju models

Our example's output:

Controller: lxd

Model       Cloud/Region         Status     Machines  Access  Last connection
controller  localhost/localhost  available         1  admin   just now
default*    localhost/localhost  available         2  admin   2019-02-02

To see the currently active controller, model, and user:

juju whoami

Our example:

Controller:  lxd
Model:       default
User:        admin

Deploying an application

Applications are contained within models and are installed via charms. By default, charms are downloaded from the online Charm Store during deployment.

To deploy a charm, such as 'redis', in the currently active model:

juju deploy redis

This results in an identically-named application ("redis") to be installed on a newly-created machine within the backing cloud. You can assign a custom name to the application by specifying that name as an argument:

juju deploy redis datastore

Adding a model

To create a model, named 'alpha', in the currently active controller:

juju add-model alpha

By default, when a model is created the currently active model becomes the new model.

Changing models

To manually change to a different model, say the original 'default' model:

juju switch default

Adding a machine

To request that two machines be created that are devoid of an application:

juju add-machine -m alpha -n 2

Here we've used the -m option to explicitly select a model (i.e. we don't want the currently active model, which at this time is 'default').

Listing machines

To change context to model 'alpha' and then list the model's machines:

juju switch alpha
juju machines

Our example:

Machine  State    DNS            Inst id        Series  AZ  Message
0        started  juju-ded876-0  bionic      Running
1        started   juju-ded876-1  bionic      Running

Deploying to a LXD container

To deploy 'apache2' to a new LXD container on existing machine '0':

juju deploy apache2 --to lxd:0

It's not necessary to explicitly target an existing machine in order to deploy a charm upon on. To deploy 'mongodb' on the second available machine ('1'):

juju deploy mongodb

Scaling up an application

To scale out the 'apache2' application by creating another instantiation (unit) of it on a new machine:

juju add-unit apache2

Like the add-machine command, the -n option is available if multiple units are desired.

Viewing the model status

The status command is one that you'll use often. It gives live information for a given model.

juju status

Our example currently shows:

Model  Controller  Cloud/Region         Version  SLA          Timestamp
alpha  lxd         localhost/localhost  2.5.0    unsupported  21:28:33Z

App      Version  Status   Scale  Charm    Store       Rev  OS      Notes
apache2           unknown      2  apache2  jujucharms   26  ubuntu  
mongodb  3.6.3    active       1  mongodb  jujucharms   52  ubuntu  

Unit        Workload  Agent  Machine  Public address  Ports                     Message
apache2/0*  unknown   idle   0/lxd/0                                             
apache2/1   unknown   idle   2                                            
mongodb/0*  active    idle   1 27017/tcp,27019/tcp,27021/tcp,28017/tcp  Unit is ready

Machine  State    DNS            Inst id              Series  AZ  Message
0        started  juju-ded876-0        bionic      Running
0/lxd/0  started   juju-ded876-0-lxd-0  bionic      Container started
1        started   juju-ded876-1        bionic      Running
2        started  juju-ded876-2        bionic      Running

The output is broken up into four sections.

The top section mentions basic information such as the names of the current model and controller ('alpha' and 'lxd' respectively), followed by the cloud name ('localhost'), what version of Juju the model is running, whether Juju is being used in a third-party context (see Managed solutions), and finally, the timestamp of the current controller.

The App section contains information at the application level. It is closely related to the providence of an application's charm. The 'Scale' tells us how many units exist for an application while the 'Rev' column shows the charm's revision number.

The Unit section contains information at the unit level. It lists them, along with information that is passed back from the unit agent. The type of data available is is very charm-specific. For instance, the 'unknown' workload message for the apache2 units is not necessarily a bad thing. It's just that the associated charm was not written to give something more insightful.

The Machine section contains information at the machine level. It lists machines by their ID (e.g. '0/lxd/0' or just '1'). The 'Inst id' is the instance id of the machine that gets passed to the cloud provider as the instance name.

Notice how the machines command output is a subset of the status command output.

Inspecting the logs

Juju logs are inspected on a per-model basis using a specific utility.

To view (tail) the logs of the 'alpha' model:

juju debug-log -m alpha

There are a number of ways to configure the behaviour of the debug-log command.

Connecting to a machine via SSH

The system user who created the controller (bootstrap command) will automatically have SSH access to all machines in the original two default models ('controller' and 'default') and any models they create afterwards.

To connect to a machine simply refer to the machine ID (from the machines command). Here we connect to machine '1' in the current model:

juju ssh 1

This command will always get you to the controller machine:

juju ssh -m controller 0

Removing an application

To remove the 'apache2' application, including all units, along with associated machines (provided they are not hosting another application's units).

juju remove-application apache2

Removing a unit

To remove just a single unit, such as 'apache2/1':

juju remove-unit apache2/1

Like the remove-application command, this command will also remove the machine if it is now devoid of units.

Removing a machine

To remove the machine whose ID is '1':

juju remove-machine 1

As a safety precaution, a machine cannot be removed if it is hosting a unit. Either remove all of its units first or, as a last resort, use the --force option.

Destroying a model

Destroying a model is a quick way to remove all applications and machines within that model. Begin anew with the creation of a new one.

To destroy the model called 'alpha':

juju destroy-model alpha

Destroying a controller

When a controller is destroyed, all its models, applications, and machines are as well.

To destroy the controller called 'lxd':

juju destroy-controller lxd

Next steps

Based on the material covered in this tutorial, we suggest the following for further reading: