Go framework extension¶
The go-framework
extension includes configuration options customised for a Go
application. This document describes all the keys that a user may interact with.
Tip
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 case you want to add extra configuration options, 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
In addition to this, you can set the configuration option to be
mandatory by setting the optional
key to false
. This will
block the charm and stop services until the configuration is supplied. For example,
if your application needs an api-token
to function correctly you can set
optional
, as shown below. This will block the charm and stop the
services until the api-token
configuration is supplied.
config:
options:
api-token:
description: The token necessary for the service to run.
type: string
optional: false
Note
A configuration with optional: false
can’t also have a default
key.
If it has both, the charm will fail to pack.
peers
, provides
, and requires
keys¶
Your charm already has some peers
, provides
, and requires
integrations, for internal purposes.
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 integrations, in each provides
and requires
block you may specify further integration endpoints, to integrate with
the following charms and bundles:
Ingress: traefik and nginx ingress integrator
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
requires:
tracing:
interface: tracing
optional: True
limit: 1
requires:
smtp:
interface: smtp
optional: True
limit: 1
Note
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
project 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 Tracing integration creates the following environment variables that you can use to configure your application:
OTEL_EXPORTER_OTLP_ENDPOINT
OTEL_SERVICE_NAME
The provided SMTP environment variables are as follows:
SMTP_HOST
SMTP_PORT
SMTP_USER
SMTP_PASSWORD_ID
SMTP_AUTH_TYPE
SMTP_TRANSPORT_SECURITY
SMTP_DOMAIN
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.
Observability¶
12-Factor charms are designed to be easily observable using the Canonical Observability Stack.
You can easily integrate your charm with Loki, Prometheus and Grafana using Juju.
juju integrate go-k8s grafana
juju integrate go-k8s loki
juju integrate go-k8s prometheus
After integration, you will be able to observe your workload using Grafana dashboards.
In addition to that you can also trace your workload code using Tempo.
To learn about how to deploy Tempo you can read the documentation here.
OpenTelemetry will automatically read the environment variables and configure the OpenTelemetry SDK to use them. See the OpenTelemetry documentation for further information about tracing.
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 project 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: Juju | Secret