# Initialization tasks

There are often initialization tasks performed by Quarkus extensions that are meant to be run once. For example, Flyway or Liquibase initialization falls into that category. But what happens when the scaling needs of an application requires more instances of the application to run? Or what happens when the application restarts?

A common environment where both of these cases are pretty common is Kubernetes. To address these challenges, Quarkus allows externalization of such tasks as Kubernetes Jobs and uses init containers to ensure that an application instance only starts once the initialization jobs have finished. With this approach even if an application has multiple replicas, the initialization logic will only run once.

This approach is reflected in the manifests generated by Kubernetes extension.

## Disabling the feature

The feature can be explicitly disabled per task (enabled by default). The default behavior can change by setting the following property to `false`:

    quarkus.kubernetes.init-task-defaults.enabled=false

or on OpenShift:

    quarkus.openshift.init-task-defaults.enabled=false

Note: All the configuration options in this guide are available on both OpenShift and Kubernetes. The rest of the guide will use Kubernetes(`quarkus.kubernetes` prefix) configuration prefix, but all the configuration options are also available for OpenShift(`quarkus.openshift` prefix) too.

In the case where we need to disable a particular task, we can use the following property:

    quarkus.kubernetes.init-tasks."<task name>".enabled=false

The task name is the name of the extension that performs the initialization. Examples:

For Flyway:

    quarkus.kubernetes.init-tasks.flyway.enabled=false

For Liquibase:

    quarkus.kubernetes.init-tasks.liquibase.enabled=false

For Liquibase Mongodb:

    quarkus.kubernetes.init-tasks.liquibase-mongodb.enabled=false

## Controlling the generated job

The job container is pretty similar to the application container, and the only thing that changes is the configured environment variables. More specifically, the following environment variable is added, to tell the job to exit right after initialization.

    QUARKUS_INIT_AND_EXIT=true

The image, image pull policy, service account, volumes, mounts and additional environment variables are inherited/copied from the deployment resource. Any customization to the original deployment resource (via configuration or extension) will also be reflected in the job.

## Controlling the generated init container

The name of the generated init container is `wait-for-${task name}` by default. Given that the init container is part of the same pod as the actual application, it will get the same service account (and therefore permissions) and volumes as the application. Further customization to the container can be done using the configuration options for init containers (see `quarkus.kubernetes.init-containers` or `quarkus.openshift.init-containers`).

Examples:

To set the `imagePullPolicy` to `IfNotPresent` on the init container that waits for the `flyway` job:

    quarkus.kubernetes.init-containers.flyway.image-pull-policy=if-not-present

To set custom command (say `custom-wait-for`) on the init container that waits for the `flyway` job:

    quarkus.kubernetes.init-containers.flyway.command=custom-wait-for

## Orchestration of the initialization tasks

The deployment resource should not start until the job has been completed. The typical pattern that is used among Kubernetes users is the use of init containers to achieve this. An init container that `waits for` the job to complete is enough to enforce that requirement.

### Using a custom wait-for container image

By default, the `wait-for` image is `groundnuty/k8s-wait-for:no-root-v1.7`. You can define another image:

    quarkus.kubernetes.init-task-defaults.wait-for-container.image=my/wait-for-image:1.0

The `imagePullPolicy` can also be configured:

    quarkus.kubernetes.init-task-defaults.wait-for-container.image-pull-policy=if-not-present

To change the `wait-for` image for a particular init container (e.g. one that waits for the `flyway` job), you can use:

    quarkus.kubernetes.init-tasks.flyway.wait-for-container.image=my/wait-for-image:1.0

You can define the `imagePullPolicy` for this particular init container with:

    quarkus.kubernetes.init-tasks.flyway.wait-for-container.image-pull-policy=if-not-present

### Configuring permissions

For an init container to be able to perform the `wait for job`, it needs to be able to perform `get` operations on the job resource. This is done automatically and the generated manifests include the required `Role` and `RoleBinding` resources.

If, for any reason, additional permissions are required either by the init container or the job, they can be configured with the Kubernetes RBAC configuration.

| The application, the init container and the job use the same `ServiceAccount` and therefore, share the same permissions.

## Extensions providing Initialization Tasks

Currently, this feature is used by the following extensions:

- Flyway

- Liquibase

- Liquibase MongoDB