Charmcraft extension 'flask-framework'

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The flask-framework Charmcraft extension includes configuration options customised for a Flask application. This document describes all the keys that a user may interact with.

If you’d like to see the full contents contributed by this extension:
See How to manage extensions.

charmcraft.yaml > config > options

You can use the predefined options (run charmcraft expand-extensions for details) but also add your own, as needed.

In the latter case, any option you define will be used to generate environment variables; a user-defined option config-option-name will generate an environment variable named FLASK_CONFIG_OPTION_NAME where the option name is converted to upper case and dashes are converted to underscores.

In either case, you will be able to set it in the usual way by running juju config <application> <option>=<value>. For example, if you define an option called token, as below, this will generate a FLASK_TOKEN environment variable, and a user of your charm can set it by running juju config <application> token=<token>.

config:
  options:
    token:
      description: The token for the service.
      type: string
      required: true

charmcraft.yaml > peers, provides, requires

Your charm already has some peers, provides, and requires integrations, for internal purposes.

Expand to view pre-loaded integrations 
peers:
  secret-storage:
    interface: secret-storage
provides:
  metrics-endpoint:
    interface: prometheus_scrape
  grafana-dashboard:
    interface: grafana_dashboard
requires:
  logging:
    interface: loki_push_api
  ingress:
    interface: ingress
    limit: 1

In addition to these, in each provides and requires block you may specifying further integration endpoints, to integrate with the following charms and bundles:

These endpoint definitions are as below:

requires:
  mysql:
    interface: mysql_client
    optional: True
    limit: 1

requires:
  postgresql:
    interface: postgresql_client
    optional: True
    limit: 1

requires:
  mongodb:
    interface: mongodb_client
    optional: True
    limit: 1

requires:
  redis:
    interface: redis
    optional: True
    limit: 1

requires:
  saml:
    interface: saml
    optional: True
    limit: 1

requires:
  s3:
    interface: s3
    optional: True
    limit: 1

To add one of these integrations, e.g. postgresql, in the charmcraft.yaml file include the appropriate requires block and integrate with juju integrate <flask charm> postgresql as usual.

After the integration has been established, the connection string will be available as an environment variable. Integration with PostgreSQL, MySQL, MongoDB or Redis provides the string as the POSTGRESQL_DB_CONNECT_STRING, MYSQL_DB_CONNECT_STRING, MONGODB_DB_CONNECT_STRING or REDIS_DB_CONNECT_STRING environment variables respectively. Furthermore, the following environment variables will be provided to your Flask application for integrations with PostgreSQL, MySQL, MongoDB or Redis:

  • <integration>_DB_SCHEME
  • <integration>_DB_NETLOC
  • <integration>_DB_PATH
  • <integration>_DB_PARAMS
  • <integration>_DB_QUERY
  • <integration>_DB_FRAGMENT
  • <integration>_DB_USERNAME
  • <integration>_DB_PASSWORD
  • <integration>_DB_HOSTNAME
  • <integration>_DB_PORT
  • <integration>_DB_NAME

Here, <integration> is replaced by POSTGRESQL, MYSQL MONGODB or REDIS for the relevant integration.

The provided SAML environment variables are as follows:

  • SAML_ENTITY_ID (required)
  • SAML_METADATA_URL (required)
  • SAML_SINGLE_SIGN_ON_REDIRECT_URL (required)
  • SAML_SIGNING_CERTIFICATE (required)

The S3 integration creates the following environment variables that you may use to configure your Flask application: :

  • S3_ACCESS_KEY (required)
  • S3_SECRET_KEY (required)
  • S3_BUCKET (required)
  • S3_REGION
  • S3_STORAGE_CLASS
  • S3_ENDPOINT
  • S3_PATH
  • S3_API_VERSION
  • S3_URI_STYLE
  • S3_ADDRESSING_STYLE
  • S3_ATTRIBUTES
  • S3_TLS_CA_CHAIN

The environment variable FLASK_BASE_URL provides the Ingress URL for an Ingress integration or the Kubernetes service URL if there is no Ingress integration.

HTTP Proxy

Proxy settings should be set as model configurations. Charms generated using the flask-framework extension will make the Juju proxy settings available as the HTTP_PROXY, HTTPS_PROXY and NO_PROXY environment variables. For example, the juju-http-proxy environment variable will be exposed as HTTP_PROXY to the Flask service.

See more: Juju | List of model configuration keys


Contributors: @econley, @javierdelapuente, @jdkandersson, @tmihoc