(Optional) By default, your dev server will target localhost:8080. If your backend is running elsewhere, you can create .env.development.local under ui folder with this content:

VITE_APP_API_URL={myApiUrl}

Navigate into the ui folder and run npm install to install the dependencies for the frontend project.
Now go to the cli/src/main/resources folder and create a application-override.yml file.

Now you have two choices:

Local mode:

Runs the Kestra server in local mode which uses a H2 database, so this is the only config you'd need:

micronaut:
  server:
    cors:
      enabled: true
      configurations:
        all:
          allowedOrigins:
            - http://localhost:5173

You can then open a new terminal and run the following command to start the backend server: ./gradlew runLocal

Standalone mode:

Runs in standalone mode which uses Postgres. Make sure to have a local Postgres instance already running on localhost:

kestra:
  repository:
    type: postgres
  storage:
    type: local
    local:
      base-path: "/app/storage"
  queue:
    type: postgres
  tasks:
    tmp-dir:
      path: /tmp/kestra-wd/tmp
  anonymous-usage-report:
    enabled: false

datasources:
  postgres:
    # It is important to note that you must use the "host.docker.internal" host when connecting to a docker container outside of your devcontainer as attempting to use localhost will only point back to this devcontainer.
    url: jdbc:postgresql://host.docker.internal:5432/kestra
    driverClassName: org.postgresql.Driver
    username: kestra
    password: k3str4

flyway:
  datasources:
    postgres:
      enabled: true
      locations:
        - classpath:migrations/postgres
      # We must ignore missing migrations as we may delete the wrong ones or delete those that are not used anymore.
      ignore-migration-patterns: "*:missing,*:future"
      out-of-order: true

micronaut:
  server:
    cors:
      enabled: true
      configurations:
        all:
          allowedOrigins:
            - http://localhost:5173

If you're doing frontend development, you can run npm run dev from the ui folder after having the above running (which will provide a backend) to access your application from localhost:5173. This has the benefit to watch your changes and hot-reload upon doing frontend changes.