Charmcraft extension 'go-framework'

The go-framework Charmcraft extension includes configuration options customised for a Go 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.

The predefined configuration options for the go-framework are:

app-port: Port in which the application should listen. The ingress will be configured using this port. The environment variable passed to the app is APP_PORT. Default value is 8080.
app-secret-key: Long secret you can use for sessions, csrf or any other thing where you need a random secret shared by all units. The environment variable passed to the app is APP_METRICS_PORT. The default value is random.
metrics-port: Port where the prometheus metrics will be scraped. The environment variable passed to the app is APP_PORT. Default value is 8080.
metrics-path: Path where the prometheus metrics will be scraped. The environment variable passed to the app is APP_METRICS_PATH. Default value is /metrics.

In the case you want to add extra configuration optoins, any option you define will be used to generate environment variables; a user-defined option config-option-name will generate an environment variable named APP_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 APP_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

`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:

Ingress: traefik and nginx ingress integrator
MySQL: machine and k8s charm
PostgreSQL: machine and k8s charm
MongoDB
Canonical Observability Stack (COS)
Redis
SAML
S3
RabbitMQ: machine and k8s charm

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

requires:
  rabbitmq:
    interface: rabbitmq
    optional: True
    limit: 1

The key optional with value False means that the charm will get blocked and stop the services if the integration is not provided.

To add one of these integrations, e.g. postgresql, in the charmcraft.yaml file include the appropriate requires block and integrate with juju integrate <go 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 Go 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 Go 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 RabbitMQ integration creates the connection string in the environment variable RABBITMQ_CONNECT_STRING. Furthermore, the following environment variables may be provided, derived from the connection string:

RABBITMQ_SCHEME
RABBITMQ_NETLOC
RABBITMQ_PATH
RABBITMQ_PARAMS
RABBITMQ_QUERY
RABBITMQ_FRAGMENT
RABBITMQ_USERNAME
RABBITMQ_PASSWORD
RABBITMQ_HOSTNAME
RABBITMQ_PORT
RABBITMQ_VHOST

The environment variable APP_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 go-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 Go service.

See more: List of model configuration keys

Background Tasks

Extra services defined in the file rockcraft.yaml^ with names ending in -worker or -scheduler will be passed the same environment variables as the main application. If there is more than one unit in the application, the services with the name ending in -worker will run in all units. The services with name ending in -scheduler will only run in one of the units of the application.

Secrets

Juju secrets can be passed as environment variables to your Go application. The secret ID has to be passed to the application as a config option in the file charmcraft.yaml file of type secret. This config option has to be populated with the secret ID, in the format secret:<secret ID>.

The environment variable name passed to the application will be:

APP_<config option name>_<key inside the secret>

The <config option name> and <key inside the secret> keywords in the environment variable name will have the hyphens replaced by underscores and all the letters capitalised.

See more: Secret

Contributors: @javierdelapuente, @econley, @jdkandersson

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