Imagine you have a FastAPI application backed up by a database such as PostgreSQL and need to deploy it. In a traditional setup, this can be quite a challenge, but with Juju you’ll find yourself deploying, configuring, scaling, integrating, monitoring, etc., your FastAPI application in no time. Let’s get started!
In this tutorial we will build a rock and Kubernetes charm for a FastAPI application using the charm SDK, so we can have a FastAPI application up and running with Juju in about 90 minutes.
rock
An Ubuntu LTS-based OCI compatible container image designed to meet security, stability, and reliability requirements for cloud-native software.
charm
A package consisting of YAML files + Python code that will automate every aspect of an application’s lifecycle so it can be easily orchestrated with Juju.
Juju
An orchestration engine for software operators that enables the deployment, integration and lifecycle management of applications using charms.
What you’ll need:
- A workstation, e.g., a laptop, with amd64 architecture which has sufficient resources to launch a virtual machine with 4 CPUs, 4 GB RAM, and a 50 GB disk
- Note that a workstation with arm64 architecture can complete the majority of this tutorial.
- Familiarity with Linux
What you’ll do:
- Set things up
- Create the FastAPI application
- Run the FastAPI application locally
- Pack the FastAPI application into a rock
- Create the charm
- Deploy the FastAPI application
- Enable
juju config fastapi-hello-world greeting=<greeting>
- Integrate with a database
- Expose the app using ingress
- Clean up environment
Set things up
Install Multipass.
See more: Multipass | How to install Multipass
Use Multipass to launch an Ubuntu VM.
There are two tracks you can follow to complete the setup process:
- A fast track approach where one command will set up nearly everything for you.
- A hands-on approach where you will set up everything yourself.
Fast track approach
To fast-track the setup, launch a VM with the name charm-dev
using the charm-dev blueprint:
multipass launch --cpus 4 --disk 50G --memory 4G --name charm-dev charm-dev
This step may take a few minutes to complete (10-15 minutes).
This is because the command downloads, installs, (updates,) and configures a number of packages, and the speed will be affected by network bandwidth (not just your own, but also that of the package sources).
However, once it’s done, you’ll have everything you’ll need.
Once the VM is up, open a shell into it:
multipass shell charm-dev
MicroK8s ingress is required to expose the FastAPI application. Enable using:
sudo microk8s enable ingress
See more: ingress^
Hands-on approach
For a more hands-on setup, use Multipass to launch an Ubuntu VM with the name charm-dev
from the 24.04 blueprint:
multipass launch --cpus 4 --disk 50G --memory 4G --name charm-dev 24.04
Once the VM is up, open a shell into it:
multipass shell charm-dev
In order to create the rock, you’ll need to install Rockcraft:
sudo snap install rockcraft --channel latest/edge --classic
LXD
will be required for building the rock. Make sure it is installed and initialised:
sudo snap install lxd
lxd init --auto
In order to create the charm, you’ll need to install Charmcraft:
sudo snap install charmcraft --channel latest/edge --classic
MicroK8s is required to deploy the FastAPI application on Kubernetes. Install MicroK8s:
sudo snap install microk8s --channel 1.31-strict/stable
sudo adduser $USER snap_microk8s
newgrp snap_microk8s
Wait for MicroK8s to be ready using sudo microk8s status --wait-ready
. Several MicroK8s add-ons are required for deployment. The MicroK8s registry is required to host the OCI image of the FastAPI application and ingress is required to expose the FastAPI application. Enable all using:
sudo microk8s enable hostpath-storage
sudo microk8s enable registry
sudo microk8s enable ingress
See more: ingress^
Juju is required to deploy the FastAPI application. Install Juju and bootstrap a development controller:
sudo snap install juju --channel 3.5/stable
mkdir -p ~/.local/share
juju bootstrap microk8s dev-controller
Create the tutorial directory
This tutorial requires version 3.0.0
or later of Charmcraft. Check the version of Charmcraft using charmcraft --version
If you have an older version of Charmcraft installed, use sudo snap refresh charmcraft --channel latest/edge
to get the latest edge version of Charmcraft.
This tutorial requires version 1.5.4
or later of Rockcraft. Check the version of Rockcraft using rockcraft --version
If you have an older version of Rockcraft installed, use sudo snap refresh rockcraft --channel latest/edge
to get the latest edge version of Rockcraft.
Finally, create a new directory for this tutorial and go inside it:
mkdir fastapi-hello-world
cd fastapi-hello-world
Create the FastAPI application
Start by creating the “Hello, world” FastAPI application that will be used for this tutorial.
Create a requirements.txt
file, copy the following text into it and then save it:
fastapi[standard]
In the same directory, copy and save the following into a text file called app.py
:
from fastapi import FastAPI
app = FastAPI()
@app.get("/")
async def root():
return {"message": "Hello World"}
Run the FastAPI application locally
Install python3-venv
and create a virtual environment:
sudo apt-get update && sudo apt-get install python3-venv -y
python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
Now that we have a virtual environment with all the dependencies, let’s run the FastAPI application to verify that it works:
fastapi dev app.py --port 8080
Test the FastAPI application by using curl
to send a request to the root endpoint. You may need a new terminal for this; if you are using Multipass use multipass shell charm-dev
to get another terminal:
curl localhost:8080
The FastAPI application should respond with {"message":"Hello World"}
. The FastAPI application looks good, so we can stop for now using ctrl + c.
Pack the FastAPI application into a rock
First, we’ll need a rockcraft.yaml
file. Rockcraft will automate its creation and tailoring for a FastAPI application by using the fastapi-framework
profile:
rockcraft init --profile fastapi-framework
The rockcraft.yaml
file will automatically be created and set the name based on your working directory. Open the file in a text editor and check that the name
is fastapi-hello-world
. Ensure that platforms
includes the architecture of your host. For example, if your host uses the ARM architecture, include arm64
in platforms
.
For this tutorial, we’ll use the name
“fastapi-hello-world” and assume you are on the amd64
platform. Check the architecture of your system using dpkg --print-architecture
. Choosing a different name or running on a different platform will influence the names of the files generated by Rockcraft.
Pack the rock:
ROCKCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true rockcraft pack
Depending on your system and network, this step can take a couple of minutes to finish.
ROCKCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS
is required whilst the FastAPI extension is experimental.
Once Rockcraft has finished packing the FastAPI rock, you’ll find a new file in your working directory with the .rock
extension:
ls *.rock -l
If you changed the name
or version
in rockcraft.yaml
or are not on an amd64
platform, the name of the .rock
file will be different for you.
The rock needs to be copied to the MicroK8s registry so that it can be deployed in the Kubernetes cluster:
rockcraft.skopeo --insecure-policy copy --dest-tls-verify=false \
oci-archive:fastapi-hello-world_0.1_amd64.rock \
docker://localhost:32000/fastapi-hello-world:0.1
See more: skopeo^
Create the charm
Create a new directory for the charm and go inside it:
mkdir charm
cd charm
We’ll need a charmcraft.yaml
, requirements.txt
and source code for the charm. The source code contains the logic required to operate the FastAPI application. Charmcraft will automate the creation of these files by using the fastapi-framework
profile:
charmcraft init --profile fastapi-framework --name fastapi-hello-world
The files will automatically be created in your working directory.
The charm depends on several libraries. Download the libraries and pack the charm:
CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft fetch-libs
CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft pack
Depending on your system and network, this step can take a couple of minutes to finish.
CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS
is required whilst the FastAPI extension is experimental.
Once Charmcraft has finished packing the charm, you’ll find a new file in your working directory with the .charm
extension:
ls *.charm -l
If you changed the name in charmcraft.yaml or are not on the amd64 platform, the name of the .charm
file will be different for you.
Deploy the FastAPI application
A Juju model is needed to deploy the application. Let’s create a new model:
juju add-model fastapi-hello-world
Now the FastAPI application can be deployed using Juju:
juju deploy ./fastapi-hello-world_amd64.charm fastapi-hello-world \
--resource app-image=localhost:32000/fastapi-hello-world:0.1
It will take a few minutes to deploy the FastAPI application. You can monitor the progress using juju status --watch 5s
. Once the status of the App has gone to active
, you can stop watching using ctrl + c.
See more: Command ‘juju status’
The FastAPI application should now be running. We can monitor the status of the deployment using juju status
which should be similar to the following output:
Model Controller Cloud/Region Version SLA Timestamp
fastapi-hello-world dev-controller microk8s/localhost 3.5.4 unsupported 13:45:18+10:00
App Version Status Scale Charm Channel Rev Address Exposed Message
fastapi-hello-world active 1 fastapi-hello-world 0 10.152.183.53 no
Unit Workload Agent Address Ports Message
fastapi-hello-world/0* active idle 10.1.157.75
Test the deployment using curl
to send a request to the root endpoint. The IP address is the Address listed in the Unit section of the juju status
output (e.g., 10.1.157.75
in the sample output above):
$ curl 10.1.157.75:8080
{"message":"Hello World"}
Configure the FastAPI application
Now let’s customise the greeting using a configuration option. We will expect this configuration option to be available in the environment variable APP_GREETING
. Go back out to the root directory of the project using cd ..
and copy the following code into app.py
:
import os
from fastapi import FastAPI
app = FastAPI()
@app.get("/")
async def root():
return {"message": os.getenv("APP_GREETING", "Hello World")}
Open rockcraft.yaml
and update the version to 0.2
. Run ROCKCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true rockcraft pack
again, then upload the new OCI image to the MicroK8s registry:
rockcraft.skopeo --insecure-policy copy --dest-tls-verify=false \
oci-archive:fastapi-hello-world_0.2_amd64.rock \
docker://localhost:32000/fastapi-hello-world:0.2
Change back into the charm directory using cd charm
. The fastapi-framework
Charmcraft extension supports adding configurations to charmcraft.yaml
which will be passed as environment variables to the FastAPI application. Add the following to the end of the charmcraft.yaml
file:
config:
options:
greeting:
description: |
The greeting to be returned by the FastAPI application.
default: "Hello, world!"
type: string
Configuration options are automatically capitalised and -
are replaced by _
. A APP_
prefix will also be added to ensure that environment variables are namespaced.
Run CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft pack
again. The deployment can now be refreshed to make use of the new code:
juju refresh fastapi-hello-world \
--path=./fastapi-hello-world_amd64.charm \
--resource app-image=localhost:32000/fastapi-hello-world:0.2
Wait for juju status
to show that the App is active
again. Verify that the new configuration has been added using juju config fastapi-hello-world | grep -A 6 greeting:
which should show the configuration option.
The grep
command extracts a portion of the configuration to make it easier to check whether the configuration option has been added.
Get the updated IP address shown in the Unit section of juju status
. Using curl 10.1.157.76:8080
shows that the response is still {"message":"Hello, world!"}
as expected. The greeting can be changed using Juju:
juju config fastapi-hello-world greeting='Hi!'
curl 10.1.157.76:8080
now returns the updated {"message":"Hi!"}
greeting.
It might take a short time for the configuration to take effect.
Integrate with a database
Now let’s keep track of how many visitors your application has received. This will require integration with a database to keep the visitor count. This will require a few changes:
- We will need to create a database migration that creates the
visitors
table - We will need to keep track how many times the root endpoint has been called in the database
- We will need to add a new endpoint to retrieve the number of visitors from the database
The charm created by the fastapi-framework
extension will execute the migrate.py
script if it exists. This script should ensure that the database is initialised and ready to be used by the application. We will create a migrate.py
file containing this logic.
Go back out to the tutorial root directory using cd ..
. Create the migrate.py
file using a text editor and paste the following code into it:
import os
import psycopg2
DATABASE_URI = os.environ["POSTGRESQL_DB_CONNECT_STRING"]
def migrate():
with psycopg2.connect(DATABASE_URI) as conn, conn.cursor() as cur:
cur.execute("""
CREATE TABLE IF NOT EXISTS visitors (
timestamp TIMESTAMP NOT NULL,
user_agent TEXT NOT NULL
);
""")
conn.commit()
if __name__ == "__main__":
migrate()
The charm will pass the Database connection string in the POSTGRESQL_DB_CONNECT_STRING
environment variable once postgres has been integrated with the charm.
Open the rockcraft.yaml
file in a text editor and update the version to 0.3
.
To be able to connect to postgresql from the FastAPI app the psycopg2-binary
dependency needs to be added in requirements.txt
. The app code also needs to be updated to keep track of the number of visitors and to include a new endpoint to retrieve the number of visitors to the app. Open app.py
in a text editor and replace its contents with the following code:
import datetime
import os
from typing import Annotated
from fastapi import FastAPI, Header
import psycopg2
app = FastAPI()
DATABASE_URI = os.environ["POSTGRESQL_DB_CONNECT_STRING"]
@app.get("/")
async def root(user_agent: Annotated[str | None, Header()] = None):
with psycopg2.connect(DATABASE_URI) as conn, conn.cursor() as cur:
timestamp = datetime.datetime.now()
cur.execute(
"INSERT INTO visitors (timestamp, user_agent) VALUES (%s, %s)",
(timestamp, user_agent)
)
conn.commit()
return {"message": os.getenv("APP_GREETING", "Hello World")}
@app.get("/visitors")
async def visitors():
with psycopg2.connect(DATABASE_URI) as conn, conn.cursor() as cur:
cur.execute("SELECT COUNT(*) FROM visitors")
total_visitors = cur.fetchone()[0]
return {"count": total_visitors}
Run ROCKCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true rockcraft pack
and upload the newly created rock to the MicroK8s registry:
rockcraft.skopeo --insecure-policy copy --dest-tls-verify=false \
oci-archive:fastapi-hello-world_0.3_amd64.rock \
docker://localhost:32000/fastapi-hello-world:0.3
The FastAPI app now requires a database which needs to be declared in the charmcraft.yaml
file. Go back into the charm directory using cd charm
. Open charmcraft.yaml
in a text editor and add the following section to the end:
requires:
postgresql:
interface: postgresql_client
optional: false
Pack the charm using CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft pack
and refresh the deployment using Juju:
juju refresh fastapi-hello-world \
--path=./fastapi-hello-world_amd64.charm \
--resource app-image=localhost:32000/fastapi-hello-world:0.3
Deploy postgresql-k8s
using Juju and integrate it with fastapi-hello-world
:
juju deploy postgresql-k8s --trust
juju integrate fastapi-hello-world postgresql-k8s
Wait for juju status
to show that the App is active
again. Get the updated IP address shown in the Unit section of juju status
. curl 10.1.157.81:8080
should still return the {"message":"Hi!"}
greeting. To check the total visitors, use curl 10.1.157.81:8080/visitors
which should return {"count":1}
after the previous request to the root endpoint and should be incremented each time the root endpoint is requested. If we perform another request to curl 10.1.157.81:8080
, curl 10.1.157.81:8080/visitors
will return {"count":2}
.
Expose the app using ingress
This step of the tutorial only works for hosts with the amd64
architecture. For other architectures, skip this step.
As a final step, let’s expose the application using ingress. Deploy the nginx-ingress-integrator
charm and integrate it with the FastAPI app:
juju deploy nginx-ingress-integrator
juju integrate nginx-ingress-integrator fastapi-hello-world
RBAC is enabled in the charm-dev
Multipass blueprint. You will need to run juju trust nginx-ingress-integrator --scope cluster
if you’re using the charm-dev
blueprint.
The hostname of the app needs to be defined so that it is accessible via the ingress. We will also set the default route to be the root endpoint:
juju config nginx-ingress-integrator \
service-hostname=fastapi-hello-world path-routes=/
Monitor juju status
until everything has a status of active
. Use curl http://fastapi-hello-world --resolve fastapi-hello-world:80:127.0.0.1
to send a request via the ingress. It should still be returning the {"message":"Hi!"}
greeting.
The --resolve fastapi-hello-world:80:127.0.0.1
option to the curl
command is a way of resolving the hostname of the request without setting a DNS record.
Clean up environment
We’ve reached the end of this tutorial. We have created a FastAPI application, deployed it locally, integrated it with a database and exposed it via ingress!
If you’d like to reset your working environment, you can run the following in the root directory for the tutorial:
# exit and delete the virtual environment
deactivate
rm -rf charm .venv __pycache__
# delete all the files created during the tutorial
rm fastapi-hello-world_0.1_amd64.rock fastapi-hello-world_0.2_amd64.rock \
fastapi-hello-world_0.3_amd64.rock rockcraft.yaml app.py \
requirements.txt migrate.py
# Remove the juju model
juju destroy-model fastapi-hello-world --destroy-storage
If you created an instance using Multipass, you can also clean it up. Start by exiting it:
exit
And then you can proceed with its deletion:
multipass delete charm-dev
multipass purge
Next steps
If you are wondering… | visit… |
---|---|
“How do I…?” | SDK How-to docs |
“How do I debug?” | Charm debugging tools |
“What is…?” | SDK Reference docs |
“Why…?”, “So what?” | SDK Explanation docs |
Contributors: @econley, @jdkandersson, @javierdelapuente