Grafana + Playwright + Docker Problems

I am using Grafana to graph one of my applications, and I wanted to export these graphs to PDF and email them periodically.

I decidede to use playwright, which is a testing framework that uses a real browser engine and run it without user interface, and it support PDF printing too (only chromium engine).

I used the following Python code:

import time
from playwright.sync_api import sync_playwright
def print_reports():
    with sync_playwright() as p:
        browser = p.chromium.launch(headless=True)
        ctx = browser.new_context()
        page = ctx.new_page()
        page.goto(f"http://nginx/grafana/")
        time.sleep(2)
        page.pdf(path="report.pdf")
        browser.close()

It worked perfeclty from my Mac, but when I tried the same code from the container, grafana started to misbehave and give this error:

If you’re seeing this Grafana has failed to load its application files

After many trial and errors, I added the following line to my code to show and page loading issues:

page.on("pageerror", lambda exc: print(f"uncaught exception: {exc}"))

and I got this error:

uncaught exception: Invalid language tag: en-US@posix

So the problem was with default language setting in the container, to resolve it I added a locale argument to the context creattion:

ctx = browser.new_context(locale="en-US")