Vercel Error 'FUNCTION_INVOCATION_TIMEOUT' when making POST request from Flask Application

Question

The Problem

Whenever I try to make a POST request to send an email using SMTPlib through my Flask web application hosted in Vercel I get the following error message FUNCTION_INVOCATION_TIMEOUT. The Flask route the I use looks as follows:

@app.route("/", methods=["GET", "POST"])
def home():
    form = ContactForm()
    if form.validate_on_submit():
        print("Sent")
        username = form.name.data
        email = form.email.data
        phone_number = form.phone.data
        message = form.message.data
        full_email = (f"Subject: Message from Personal Website\n\n{message.encode('utf-8')}\n\n\n"
                      f"From: {username}\nEmail: {email}\nPhone Number: {phone_number}")
        with smtplib.SMTP("smtp.gmail.com") as connection:
            connection.starttls()
            connection.login(user=USERNAME,
                             password=PASSWORD)
            connection.sendmail(from_addr=USERNAME,
                                to_addrs=USERNAME,
                                msg=full_email)
            return redirect(url_for("receive_data"))
    return render_template("index.html",
                           form=form,
                           year=str(CURRENT_YEAR))

Also, I am using the default vercel.json file as:

{
    "version": 2,
    "builds": [
        {
        "src":"app.py",
        "use":"@vercel/python"
        }
    ],
    "routes": [
        {
        "src":"/(.*)",
        "dest":"app.py"
        }
    ]
}

The file structure of my application is:

my-flask-app/
│
├── static
│     ├── assets
│     ├── files
│     └── images
├── templates  
├── app.py
├── flaskforms.py
├── Procfile
├── README.md
├── requirements.txt
└── vercel.json

Things I've tried

I tried extending the timeout duration using the function property within the vercel.json file as in the code below. However, this creates a deploy error in Vercel.

{
    "version": 2,
    "builds": [
        {
        "src":"app.py",
        "use":"@vercel/python"
        }
    ],
    "routes": [
        {
        "src":"/(.*)",
        "dest":"app.py"
        }
    ],
    "functions": {
    "app.py": {
      "maxDuration": 60
    }
  }
}

I think that the problem is the time Vercel takes to run a serverless function. However, all the solution I've seen so far apply for NodeJS applications. If anyone could provide me with some advise, I would appreciate it a lot.

Answer 1

Try the Asynchronous Email Sending which may solve this FUNCTION_INVOCATION_TIMEOUT