How to manage applications

tmihoc · 17 December 2021 13:09

See also: Application

This document shows how to manage applications with Juju.

Deploy an application

To deploy an application, find and deploy a charm / bundle that delivers it.

See more: How to deploy a charm / charm bundle

Troubleshooting:

Machines:

Deploy on machines consists of the following steps: Provision resources/a machine M from the relevant cloud, via cloud-init maybe network config, download the jujud binaries from the controller, start jujud.

For failure at any point, retry the deploy command with the --debug and --verbose flags:

juju deploy <charm> --debug --verbose

If it still fails, connect to the machine and examine the logs.

See more: How to manage logs > View the log files, How to troubleshoot your deployment

Kubernetes:

Deploy on Kubernetes includes creating a Kubernetes pod and in it charm and workload containers. To troubleshoot, inspect these containers with kubectl:


kubectl exec <pod> -itc <container> -n <namespace> -- bash

View details about an application

To view more information about a deployed application, run the show-application command followed by the application name or alias:

juju show-application <application name or alias >

By specifying various flags you can also specify a model, or an output format or file.

See more: juju show-application

The terraform juju client does not support this. Please use the juju client.

To view details about an application on python-libjuju, you may use various get_* methods that are defined for applications.

For example, to get the config for an application, call get_config() method on an Application object:

config = await my_app.get_config()

See more: Application (module), Application.get_config (method), Application (methods)

Set the machine base for an application

Only for machine clouds.

You can set the base for the machines provisioned by Juju for your application’s units either during deployment or after.

Set the machine base during deployment. To set the machine base during deployment, run the deploy command with the --base flag followed by the desired compatible base. For example:

juju deploy ubuntu --base ubuntu@20.04

Set the machine base after deployment. (starting with Juju 4.0, this is no longer possible) To set the machine base after deployment, run the set-application-base command followed by the name of the application and the desired compatible base. (This will affect any future units added to the application.) For example:

juju set-application-base ubuntu ubuntu@20.04

See more: juju set-application-base

[TBA]

Trust an application with a credential

Some applications may require access to the backing cloud in order to fulfil their purpose (e.g., storage-related tasks). In such cases, the remote credential associated with the current model would need to be shared with the application. When the Juju administrator allows this to occur the application is said to be trusted.

An application can be trusted during deployment or after deployment.

Trust an application during deployment. To trust an application during deployment, run the deploy command with the --trust flag. E.g., below we trust

juju deploy --trust ...

See more: juju deploy --trust

Trust an application after deployment. To trust an application after deployment, use the trust command:

juju trust <application>

By specifying various flags, you can also use this command to remove trust from an application, or to give an application deployed on a Kubernetes model access to the full Kubernetes cluster, etc.

See more: juju trust

To trust an application with a credential, in the juju_application resource definition, add a trust attribute and set it to true:

resource "juju_application" "this" {
  model = juju_model.development.name

  charm {
    name     = "hello-kubecon"
  }

    trust = true
}

See more: juju_application (resource)

To trust an application during deployment in python-libjuju, you may call the Model.deploy() with the trust parameter:

await my_model.deploy(..., trust=True, ...)

To trust an application after deployment, you may use the Application.set_trusted() method:

await my_app.set_trusted(True)

See more: Model.deploy() (method), Application.set_trusted (method)

See also: Application.get_trusted (method)

Run an application action

See also: Action

See more: How to manage actions

Configure an application

See also: Application configuration

Most charms ship with a sensible default configuration out of the box. However, for some use cases, it may be desirable or necessary to override the default application configuration options.

Get values. The way to view the existing configuration for an application depends on whether the application has been deployed or not.

To view the configuration options of an application that you have not yet deployed,
- if its charm is on Charmhub, inspect its Configurations page; for example: Charmhub | Deploy Mediawiki using Charmhub - The Open Operator Collection.
- if its charm is local on your machine, inspect its config.yaml file.
To view the configuration values for a deployed application, run the config command followed by the name of the application. For example:

juju config mediawiki

Expand to view a sample output

application: mediawiki
charm: mediawiki
settings:
  admins:
    description: Admin users to create, user:pass
    is_default: true
    type: string
    value: ""
  debug:
    description: turn on debugging features of mediawiki
    is_default: true
    type: boolean
    value: false
  logo:
    description: URL to fetch logo from
    is_default: true
    type: string
    value: ""
  name:
    description: The name, or Title of the Wiki
    is_default: true
    type: string
    value: Please set name of wiki
  server_address:
    description: The server url to set "$wgServer". Useful for reverse proxies
    is_default: true
    type: string
    value: ""
  skin:
    description: skin for the Wiki
    is_default: true
    type: string
    value: vector
  use_suffix:
    description: If we should put '/mediawiki' suffix on the url
    is_default: true
    type: boolean
    value: true

See more: juju config

Set values. You can set configuration values for an application during deployment or later.

To set configuration values for an application during deployment, run the deploy command with the --config flag followed by the relevant key=value pair. For example, the mediawiki charm allows users to configure the name of the deployed application; below, we set it to my media wiki:

juju deploy mediawiki --config name='my media wiki'

To pass multiple values, you can repeat the flag or store the values into a config file and pass that as an argument.

See more: juju deploy --config

To set configuration values for an application post deployment, run the config command followed by the name of the application and the relevant (list of space-separated) key=value pair(s). For example, the mediawiki charm provides a name and a skin configuration key; below we set both:

juju config mediawiki name='Juju Wiki'  skin=monoblock

By exploring various options you can also use this command to pass the pairs from a YAML file or to reset the keys to their default values.

See more: juju config

To configure an application, in its resource definition add a config map with the key=value pairs you want (from the list of configs available for the charm).

resource "juju_application" "this" {
  model = juju_model.development.name

  charm {
    name = "hello-kubecon"
  }

  config = {
    redirect-map = "https://demo"      
   }    
}

See more: juju_application (resource)

Get values. To view the existing configuration for an application on python-libjuju, you may use the Application.get_config() method:

config = await my_app.get_config()

Set values. To set configuration values for an application on python-libjuju:

To configure an application at deployment, simply provide a config map during the Model.deploy() call:

await my_model.deploy(..., config={'redirect-map':'https://demo'}, ...)

To configure an application post deployment, you may use the Application.set_config() method, similar to passing config in the deploy call above:

await my_app.set_config(config={'redirect-map':'https://demo'})

See more: Model.deploy() (method), Application.set_config (method), Application.get_config (method)

Scale an application

See also: Scaling

Scale an application vertically

To scale an application vertically, set constraints for the resources that the application’s units will be deployed on.

See more: How to manage constraints for an application

Scale an application horizontally

To scale an application horizontally, control the number of units.

See more: How to control the number of units

Make an application highly available

See also: High availability

Find out if the charm delivering the application supports high availability natively or not. If the latter, find out what you need to do. This could mean integrating with a load balancing reverse proxy, configuring storage etc.

See more: Charmhub > <your charm of interest>

Scale up horizontally as usual.

See more: How to scale an application horizontally

Expand to view an example featuring the machine charm for Wordpress

The wordpress charm supports high availability natively, so we can proceed to scale up horizontally:

juju add-unit wordpress

Expand to view an example featuring the machine charm for Mediawiki

The mediawiki charm needs to be placed behind a load balancing reverse proxy. We can do that by deploying the haproxy charm, integrating the haproxy application with wordpress, and then scaling the wordpress application up horizontally:

# Suppose you have a deployment with mediawiki and mysql and you want to scale mediawiki.
juju deploy mediawiki
juju deploy mysql

# Deploy haproxy and integrate it with your existing deployment, then expose haproxy:
juju deploy haproxy
juju integrate mediawiki:db mysql
juju integrate mediawiki haproxy
juju expose haproxy

# Get the proxy's IP address:
juju status haproxy

# Finally, scale mediawiki up horizontally 
# (since it's a machine charm, use 'add-unit') 
# by adding a few more units:
juju add-unit -n 5 mediawiki

Every time a unit is added to an application, Juju will spread out that application’s units, distributing them evenly as supported by the provider (e.g., across multiple availability zones) to best ensure high availability. So long as a cloud’s availability zones don’t all fail at once, and the charm and the charm’s application are well written (changing leaders, coordinating across units, etc.), you can rest assured that cloud downtime will not affect your application.

See more: Charmhub | wordpress, Charmhub | mediawiki, Charmhub | haproxy

Integrate an application with another application

See more: How to manage relations

Manage an application’s public availability over the network

Expose an application. By default, once an application is deployed, it is only reachable by other applications in the same Juju model. However, if the particular deployment use case requires for the application to be reachable by Internet traffic (e.g. a web server, Wordpress installation etc.), Juju needs to tweak the backing cloud’s firewall rules to allow Internet traffic to reach the application. This is done with the juju expose command.

After running a juju expose command, any ports opened by the application’s charmed operator will become accessible by any public or private IP address.

Assuming the wordpress application has been deployed (and a relation has been made to the deployed database mariadb), the following command can be used to expose the application outside the Juju model:

juju expose wordpress

When running juju status, its output will not only indicate whether an application is exposed or not, but also the public address that can be used to access each exposed application:

App        Version  Status  Scale  Charm      Rev  Exposed  Message
mariadb    10.1.36  active      1  mariadb      7  no       
wordpress           active      1  wordpress    5  yes      exposed

Unit          Workload  Agent  Machine  Public address  Ports   Message
mariadb/0*    active    idle   1        54.147.127.19           ready
wordpress/0*  active    idle   0        54.224.246.234  80/tcp

The command also has flags that allow you to expose just specific endpoints of the application, or to make the application available to only specific CIDRs or spaces. For example:

juju expose percona-cluster --endpoints db-admin --to-cidrs 10.0.0.0/24

[note type=information]
To override an initial `expose` command, run the command again with the new desired specifications.
[/note]

See more: juju expose

Inspect exposure.

To view details of how the application has been exposed, run the show-application command. Sample session:

$ juju show-application percona-cluster
percona-cluster:
  ...
  exposed: true
  exposed-endpoints:
    "":
      expose-to-cidrs:
      - 0.0.0.0/0
      - ::/0
    db-admin:
      expose-to-cidrs:
      - 192.168.0.0/24
      - 192.168.1.0/24
  ...

See more: juju show-application

Unexpose an application. The juju unexpose command can be used to undo the firewall changes and once again only allow the application to be accessed by applications in the same Juju model:

juju unexpose wordpress

You can again choose to unexpose just certain endpoints of the application. For example, running juju unexpose percona-cluster --endpoints db-admin will block access to any port ranges opened for the db-admin endpoint but still allow access to ports opened for all other endpoints:

juju unexpose percona-cluster --endpoints db-admin

See more: juju unexpose

Expose. To expose an application over a network, in its resource definition use an expose attribute:

resource "juju_application" "this" {
  model = juju_model.development.name

  charm {
    name = "hello-kubecon"
  }

  expose = {}
}

This will expose all of the application’s endpoints. To restrict exposure to just specific endpoints, spaces, or CIDRs, specify nested attributes.

See more: juju_application > expose > nested schema

Unexpose. To unexpose an application, remove the expose attribute from its resource definition.

To expose some or all endpoints of an application over a network, you may use the Application.expose() method, as follows:

await my_app.expose(exposed_endpoints=None) # everything's reachable from 0.0.0.0/0.

To expose to specific CIDRs or spaces, you may use an ExposedEndpoint object to describe that, as follows:

# For spaces
await my_app.expose(exposed_endpoints={"": ExposedEndpoint(to_spaces=["alpha"]) })

# For cidrs
await my_app.expose(exposed_endpoints={"": ExposedEndpoint(to_cidrs=["10.0.0.0/24"])})

# You may use both at the same time too
await my_app.expose(exposed_endpoints={
            "ubuntu": ExposedEndpoint(to_spaces=["alpha"], to_cidrs=["10.0.0.0/24"])
        })

To unexpose an application, use the Application.unexpose() method:

await my_app.unexpose() # unexposes the entire application

await my_app.unexpose(exposed_endpoints=["ubuntu"]) # unexposes the endpoint named "ubuntu"

See more: Exposed Endpoint (methods), Application.expose(), Application.unexpose()

Manage constraints for an application

See also: Constraint

Set values. You can set constraints for an application during deployment or later.

To set constraints for an application during deployment, run the deploy command with the --constraints flag followed by the relevant key-value pair or a quotes-enclosed list of key-value pairs. For example, to deploy MySQL on a resource that has at least 6 GiB of memory and 2 CPUs:

juju deploy mysql --constraints "mem=6G cores=2"

Expand to see more examples

Assuming a LXD cloud, to deploy PostgreSQL with a specific amount of CPUs and memory, you can use a combination of the instance-type and mem constraints, as below – instance-type=c5.large maps to 2 CPUs and 4 GiB, but mem overrides the latter, such that the result is a machine with 2 CPUs and 3.5 GiB of memory.

juju deploy postgresql --constraints "instance-type=c5.large mem=3.5G"

To deploy Zookeeper to a new LXD container (on a new machine) limited to 5 GiB of memory and 2 CPUs, execute:

juju deploy zookeeper --constraints "mem=5G cores=2" --to lxd

To deploy two units of Redis across two AWS availability zones, run:

juju deploy redis -n 2 --constraints zones=us-east-1a,us-east-1d

See more: juju deploy --constraints

If you want to use the image-id constraint with juju deploy:
You must also use the --base flag of the command. The base specified via --base will be used to determine the charm revision deployed on the resource created with the image-id constraint.

See more: juju deploy --base

To set constraints for an application after deployment, run the set-constraints command followed by the desired ("-enclosed list of) key-value pair(s), as below. This will affect any future units you may add to the application.

juju set-constraints mariadb cores=2

Pro tip: To reset a constraint key to its default value, run the command with the value part empty (e.g., juju deploy apache2 --constraints mem= ).

See more: juju set-constraints

Get values. To view an application’s current constraints, use the constraints command:

juju constraints mariadb

See more: juju constraints

To set constraints for an application, in its resource definition specify a constraints attribute followed by a quotes-enclosed, space-separated list of key=value pairs. For example:

resource "juju_application" "this" {
  model = juju_model.development.name

  charm {
    name = "hello-kubecon"
  }

  constraints = "mem=6G cores=2"

}

See more: juju_application (resource)

Set values. To set constraints for application in python-libjuju:

To set at deployment, simply provide a constraints map during the Model.deploy() call:

await my_model.deploy(..., constraints={, 'arch': 'amd64', 'mem': 256}, ...)

To set constraints post deployment, you may use the Application.set_contraints() method, similar to passing constraints in the deploy call above:

await my_app.set_constraints(constraints={, 'arch': 'amd64', 'mem': 256})

Get values. To see what constraints are set on an application, use the Application.get_constraints() method:

await my_app.get_constraints()

See more: Model.deploy() (method), Application.set_contraints(), Application.get_constraints (method)

Change space bindings for an application

See also: Binding

You can set space bindings for an application during deployment or post-deployment. In both cases you can set either a default space for the entire application or a specific space for one or more individual application endpoints or both.

To change space bindings for an application during deployment, use the deploy command with the bind flag followed by the name of the application and the name of the default space and/or key-value pairs consisting of specific application endpoints and the name of the space that you want to bind them to. For example (where public is the name of the space that will be used as a default):

juju deploy <application> --bind "public db=db db-client=db admin-api=public"

See more: juju deploy --bind

To change space bindings for an application after deployment, use the bind command followed by the name of the application and the name of the default space and/or key-value pairs consisting of specific application endpoints and the name of the space that you want to bind them to. For example:

juju bind <application> new-default endpoint-1=space-1

See more: juju bind

To set space bindings for an application, in its resource definition specify an endpoint_bindings with a space key, to set a default for the entire application, and/or a space and an endpoint key, to set the space binding for a particular application endpoint. For example, below all the application’s endpoints are bound to the public space except for the juju-info endpoint, which will be bound to the private space:

resource "juju_application" "application_three" {
  model = resource.juju_model.testmodel.name
  charm {
    name = "juju-qa-test"
  }
  units = 0
  endpoint_bindings = [
    {
      "space" = "public"
    }
    {
      "space" = "private"
      "endpoint" = "juju-info"
    }
  ]
}

See more: juju_application > endpoint_bindings

To set bindings for an application on python-libjuju, simply pass the bind parameter at the Model.deploy() call:

await my_model.deploy(..., bind="db=db db-client=db public admin-api=public", ...)

Python-libjuju currently doesn’t support resetting space bindings post deployment, please use the juju-cli for that.

See more: Model.deploy() (method)

Upgrade an application

To upgrade an application, update its charm.

See more: How to update a charm

Remove an application

See also: Removing things

To remove an application, run the remove-application command followed by the name of the application. For example:

juju remove-application apache2

It can take a while for the application to be completely removed but if juju status reveals that the application is listed as ‘dying’, but also reports an error state, then the removed application will not go away. See the section below for how to manage applications stuck in a dying state.

This will remove all of the application’s units. All associated resources will also be removed providing they are not hosting containers or another application’s units.

If persistent storage is in use by the application it will be detached and left in the model. However, the --destroy-storage option can be used to instruct Juju to destroy the storage once detached.

Removing an application which has relations with another application will terminate that relation. This may adversely affect the other application.

As a last resort, use the --force option (in v.2.6.1).

See more: juju remove-application

Troubleshooting:

One or more units are stuck in error state

If the status of one or more of the units being removed is error, Juju will not proceed until the error has been resolved or the remove applications command has been run again with the force flag.

See more: How to mark unit errors as resolved

To remove an application, remove its resource definition from your Terraform plan.

See more: juju_application (resource)

To remove an application from a model in python-libjuju, you have two choices:

If you have a reference to a connected model object (connected to the model you’re working on), then you may use the Model.remove_application() method:

await my_model.remove_application(my_app.name)

If you have a reference to the application you want to remove, then you may use the Application.destroy() directly on the application object you want to remove:

await my_app.destroy()

See more: Model.remove_application (method), Application.destroy (method)

Behind the scenes, the application removal consists of multiple different stages. If something goes wrong, it can be useful to determine in which step it happened. The steps are the following:

The client tells the controller to remove the application.
The controller signals to the application (charm) that it is going to be destroyed.
The charm breaks any relations to its application by calling relationship-broken and relationship-departed.
The charm calls its ‘stop hook’ which should:
- Stop the application
- Remove any files/configuration created during the application lifecycle
- Prepare any backup(s) of the application that are required for restore purposes.
The application and all its units are then removed.
In the case that this leaves machines with no running applications, the machines are also removed.

Contributors: @achilleasa , @cderici, @james-garner, @hmlanigan , @nvinuesa , @pedroleaoc , @pmatulis , @stephanpampel , @timClicks , @tmihoc

pedroleaoc · 7 April 2022 08:31

pedroleaoc · 14 October 2022 11:31

pmatulis · 19 July 2023 16:04

There used to be a section on deploying to specific machines. This is a very common use case with enterprise workloads and it would be great to have it again. The deploy help page is super long to point people at.

ameberg · 3 November 2023 14:54

There is a broken link here

https://juju.is/t//5476#heading--upgrade-an-application

I have updated containerd config but the changes are not getting pushed out the machines. Is it documented anywhere how juju/charms poll for app changes, polling frequency ?

camille.rodriguez1 · 4 December 2023 19:47

It would be useful to add a full example on upgrading a charm to a latest version.

tmihoc · 9 February 2024 14:10

@camille.rodriguez1 Sorry for the late reply. In the applications doc I’ve clarified that updating an application means updating the charm, and link to the doc on managing charms: How to manage applications In the doc on managing charms I’ve added an expand box with a full example for PostgreSQL: How to manage charms

tmihoc · 9 February 2024 14:26

@pmatulis Sorry for the very late reply. I’ve updated that section with an expand box with examples of placement directives for various clouds.

tmihoc · 9 February 2024 14:33

@ameberg : Sorry for the late reply. I’m not sure I understand your question entirely, but here is what I can say: Juju will poll Charmhub once a day to check for updates. The poll will cause juju status to indicate a newer charm version is available. The user can then update the charm to that version, if they wish to. I’ve updated the doc to clarify this.