FastAPI framework extension¶
The fastapi-framework
extension includes configuration options
customised for a FastAPI 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.
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 APP_CONFIG_OPTION_NAME
where
the option name is converted to upper case, dashes will be converted to
underscores and the APP_
prefix will be added.
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.
Relations¶
Your charm already has the following peers
, provides
, and requires
relations, as they were automatically supplied by the FastAPI extension:
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 relations, in each provides
and requires
block you may specify further relations, to integrate with
the following charms:
Relation |
Endpoint definition |
---|---|
Ingress traefik and nginx ingress integrator |
Already available in the charm |
MySQL machine and Kubernetes charm |
requires:
mysql:
interface: mysql_client
optional: True
limit: 1
|
PostgreSQL machine and Kubernetes charm |
requires:
postgresql:
interface: postgresql_client
optional: True
limit: 1
|
MongoDB charm |
requires:
mongodb:
interface: mongodb_client
optional: True
limit: 1
|
Already available in the charm |
|
Redis charm |
requires:
redis:
interface: redis
optional: True
limit: 1
|
SAML charm |
requires:
saml:
interface: saml
optional: True
limit: 1
|
S3 charm |
requires:
s3:
interface: s3
optional: True
limit: 1
|
RabbitMQ machine and Kubernetes charm |
requires:
rabbitmq:
interface: rabbitmq
optional: True
limit: 1
|
Tempo charm |
requires:
tracing:
interface: tracing
optional: True
limit: 1
|
SMTP charm |
requires:
smtp:
interface: smtp
optional: True
limit: 1
|
OpenFGA charm |
requires:
openfga:
interface: openfga
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 relations, e.g., PostgreSQL, in the
project file, include the appropriate requires
block and
integrate with juju integrate <fastapi charm> postgresql
as usual.
Environment variables¶
Each relation adds its own environment variables to your FastAPI app. Some are required, meaning they must be set for the relation to function.
The environment variable APP_BASE_URL
provides the Ingress URL
for an Ingress relation or the Kubernetes service URL if there is no
Ingress relation.
Relation |
Environment variables |
---|---|
PostgreSQL |
|
MySQL |
|
MongoDB |
|
Redis |
|
SAML |
|
S3 |
|
RabbitMQ |
|
Tracing |
|
SMTP |
|
OpenFGA |
|
HTTP Proxy¶
Proxy settings should be set as model configurations. Charms generated
using the fastapi-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 FastAPI
service.
See more: Juju | 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 fastapi-k8s grafana
juju integrate fastapi-k8s loki
juju integrate fastapi-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.
Regarding the migrate.sh
file¶
If your app depends on a database it is common to run a database
migration script before app startup which, for example, creates or
modifies tables. This can be done by including the migrate.sh
script
in the root of your project. It will be executed with the same
environment variables and context as the FastAPI application.
If the migration script fails, the app won’t be started and the app charm will go into blocked state. The migration script will be run on every unit and it is assumed that it is idempotent (can be run multiple times) and that it can be run on multiple units at the same time without causing issues. This can be achieved by, for example, locking any tables during the migration.
Secrets¶
Juju secrets can be passed as environment variables to your FastAPI 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