(manage-applications)= # How to manage applications > See also: {ref}`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: {ref}`deploy-a-charm` ````{note} - **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: ```text juju deploy --debug --verbose ``` If it still fails, connect to the machine and examine the logs. > See more: {ref}`manage-logs`, {ref}`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`: ```text kubectl exec -itc -n -- 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: ```text juju show-application ``` By specifying various flags you can also specify a model, or an output format or file. > See more: {ref}`command-juju-deploy` ## 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: ```text 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: ```text juju set-application-base ubuntu ubuntu@20.04 ``` > See more: {ref}`command-juju-set-application-base` (trust-an-application-with-a-credential)= ## 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 ```text juju deploy --trust ... ``` > See more: {ref}`command-juju-deploy` **Trust an application after deployment.** To trust an application after deployment, use the `trust` command: ```text juju trust ``` 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: {ref}`command-juju-trust` ## Run an application action > See also: {ref}`action` > > See more: {ref}`manage-actions` (configure-an-application)= ## Configure an application > See also: {ref}`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: https://charmhub.io/mediawiki/configure. - 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: ``` text juju config mediawiki ``` ````{dropdown} Expand to view a sample output ``` text 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: {ref}`command-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](https://charmhub.io/mediawiki/configure); below, we set it to `my media wiki`: ```text 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: {ref}`command-juju-deploy` - 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](https://charmhub.io/mediawiki/configure); below we set both: ``` text 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: {ref}`command-juju-config` (scale-an-application)= ## Scale an application > See also: {ref}`scaling` (scale-an-application-vertically)= ### 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: {ref}`manage-constraints-for-an-application` (scale-an-application-horizontally)= ### Scale an application horizontally To scale an application horizontally, control the number of units. > See more: {ref}`control-the-number-of-units` (make-an-application-highly-available)= ## Make an application highly available > See also: {ref}`high-availability` 1. 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 > ` See more: {ref}`scale-an-application-horizontally` ````{dropdown} 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: ```text juju add-unit wordpress ``` ```` ````{dropdown} 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: ``` text # 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`](https://charmhub.io/wordpress), [Charmhub | `mediawiki`](https://charmhub.io/mediawiki), [Charmhub | `haproxy`](https://charmhub.io/haproxy) ## Integrate an application with another application > See more: {ref}`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. ```{note} 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: ```text 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: ```text 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: ```text juju expose percona-cluster --endpoints db-admin --to-cidrs 10.0.0.0/24 ``` ```{important} To override an initial `expose` command, run the command again with the new desired specifications. ``` > See more: {ref}`command-juju-expose` **Inspect exposure.** To view details of how the application has been exposed, run the `show-application` command. Sample session: ```text $ 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: {ref}`command-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: ``` text 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: ```text juju unexpose percona-cluster --endpoints db-admin ``` > See more: {ref}`command-juju-unexpose` (manage-constraints-for-an-application)= ## Manage constraints for an application > See also: {ref}`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: ``` text juju deploy mysql --constraints "mem=6G cores=2" ``` ````{dropdown} 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. ``` text 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: ``` text juju deploy zookeeper --constraints "mem=5G cores=2" --to lxd ``` To deploy two units of Redis across two AWS availability zones, run: ``` text juju deploy redis -n 2 --constraints zones=us-east-1a,us-east-1d ``` ```` > See more: {ref}`command-juju-deploy` ```{caution} **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: {ref}`command-juju-deploy` - 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. ``` text juju set-constraints mariadb cores=2 ``` ```{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: {ref}`command-juju-set-constraints` **Get values.** To view an application's current constraints, use the `constraints` command: ``` text juju constraints mariadb ``` > See more: {ref}`command-juju-constraints` ## Change space bindings for an application 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): ```text juju deploy --bind "public db=db db-client=db admin-api=public" ``` > See more: {ref}`command-juju-deploy` - 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: ```text juju bind new-default endpoint-1=space-1 ``` > See more: {ref}`command-juju-bind` (upgrade-an-application)= ## Upgrade an application To upgrade an application, update its charm. > See more: {ref}`update-a-charm` ## Remove an application > See also: {ref}`removing-things` To remove an application, run the `remove-application` command followed by the name of the application. For example: ```text 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: {ref}`command-juju-remove-application` ````{note} Troubleshooting: ````{dropdown} 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: {ref}`mark-unit-errors-as-resolved` ``` ```` 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.