upgrades

🔄 Upgrade Your FastAPI Applications with Zero Downtime

The fastapi-serve library is a versatile tool that not only helps you deploy FastAPI applications to the cloud but also ensures zero downtime during application upgrades. This tutorial walks you through the process of testing zero downtime upgrades for your FastAPI applications.

📁 Directory structure

Here's the directory structure of the FastAPI app:

.
├── main.py            # The FastAPI app
├── README.md          # This README file
├── requirements.txt   # The requirements file for the FastAPI app
└── zero_downtime.py   # Python script to check service availability and version updates

This template application provides a simple /health endpoint and an /endpoint that responds with a Hello: World JSON object. We'll first deploy the application, then run a script that continually checks these endpoints. We'll then update the application, redeploy it, and verify that the version of the app was updated without any downtime.

# main.py
import os

from fastapi import FastAPI
from pydantic import BaseModel, Field

__version__ = "0.0.1"

app = FastAPI()

class Health(BaseModel):
    status: str
    version: str = __version__
    revision: str = Field(default_factory=lambda: os.environ.get("K_REVISION", "0.0.0"))

@app.get("/health")
def health():
    return Health(status="ok")

@app.get("/endpoint")
def endpoint():
    return {"Hello": "World"}

🐳 Deploy the FastAPI app

Let's start with deploying the app.

fastapi-serve deploy jcloud main:app

╭─────────────────────────┬────────────────────────────────────────────────────────────────────╮
│ App ID                  │                         fastapi-3a8d2d474f                         │
├─────────────────────────┼────────────────────────────────────────────────────────────────────┤
│ Phase                   │                              Serving                               │
├─────────────────────────┼────────────────────────────────────────────────────────────────────┤
│ Endpoint                │              https://fastapi-3a8d2d474f.wolf.jina.ai               │
├─────────────────────────┼────────────────────────────────────────────────────────────────────┤
│ App logs                │                       https://cloud.jina.ai/                       │
├─────────────────────────┼────────────────────────────────────────────────────────────────────┤
│ Base credits (per hour) │                  10.104 (Read about pricing here)                  │
├─────────────────────────┼────────────────────────────────────────────────────────────────────┤
│ Swagger UI              │            https://fastapi-3a8d2d474f.wolf.jina.ai/docs            │
├─────────────────────────┼────────────────────────────────────────────────────────────────────┤
│ OpenAPI JSON            │        https://fastapi-3a8d2d474f.wolf.jina.ai/openapi.json        │
╰─────────────────────────┴────────────────────────────────────────────────────────────────────╯

💻 Check service availability and version

The zero_downtime.py script continuously checks the /health endpoint and reports the status and version of the service. Run the script in your terminal:

python zero_downtime.py https://fastapi-3a8d2d474f.wolf.jina.ai

Service status: ok, Version: 0.0.1, Revision: gateway-00001
Service status: ok, Version: 0.0.1, Revision: gateway-00001
Service status: ok, Version: 0.0.1, Revision: gateway-00001

As you can see, the service is up and running, and the version is 0.0.1.

🔄 Upgrade the FastAPI app

Let's modify the FastAPI app. We'll change the version number __version__ and the response of the /endpoint endpoint to Hello: Universe.

# main.py
import os

from fastapi import FastAPI
from pydantic import BaseModel, Field

__version__ = "0.0.2"

app = FastAPI()

class Health(BaseModel):
    status: str
    version: str = __version__
    revision: str = Field(default_factory=lambda: os.environ.get("K_REVISION", "0.0.0"))

@app.get("/health")
def health():
    return Health(status="ok")

@app.get("/endpoint")
def endpoint():
    return {"Hello": "Universe"}

Then, redeploy your app with the new changes. Don't forget to use the same app ID as before.

fastapi-serve deploy jcloud main:app --app-id fastapi-3a8d2d474f

💻 Check service availability and version Again

While the update is going on, let's start another terminal and run the zero_downtime.py script again:

python zero_downtime.py https://fastapi-3a8d2d474f.wolf.jina.ai

...
Service status: ok, Version: 0.0.1, Revision: gateway-00001
Service status: ok, Version: 0.0.1, Revision: gateway-00001
Service status: ok, Version: 0.0.1, Revision: gateway-00001
Version updated from 0.0.1 to 0.0.2
Service status: ok, Version: 0.0.2, Revision: gateway-00002
Service status: ok, Version: 0.0.2, Revision: gateway-00002
Service status: ok, Version: 0.0.2, Revision: gateway-00002
...

Eventually, you'll see that the version has been updated to 0.0.2 without any downtime. The zero_downtime.py script also reports the revision number, which is incremented every time the app is updated. check

🎯 Wrapping up

With fastapi-serve, you gain the ability to perform zero-downtime upgrades, eliminating service disruptions and enhancing your application's reliability by providing your users with constant access even during updates. Users don't need to deal with application downtime or manually check for updates.