Connection Error on Local Streamlit App - Works on Streamlit Cloud

Using Streamlit
1

Issue Description:
I have developed a Streamlit application for helping coaches. The app works flawlessly when deployed via GitHub on Streamlit Cloud, but I encounter persistent connection issues when running it locally on my machine.

Environment:
-OS: Windows 10
-Python Version: 3.10
-Streamlit Version: Latest

Issue
When I execute streamlit run app.py in my VS terminal, the app opens in my local http://localhost:8501. I see my app. But when I press, an actionable button (e.g., “Generate”), the app runs (indicated by “RUNNING” status), but then it hangs with a “CONNECTING” message in the upper right corner. Eventually, I receive the following error:
Connection error
Is Streamlit still running? If you accidentally stopped Streamlit, just restart it in your terminal:
I get the same message every time I try to execute the app from the terminal.

Steps Taken:

  • Cleared Streamlit cache programmatically using st.cache_data.clear().
  • Cleared browser history and cache (Google Chrome).
  • Simplified button callback to isolate the issue.
  • Added logging and diagnostics to trace the problem, identifying it might be related to solver.Solve(model) in the CP-SAT solver from OR-Tools.

Imports
import streamlit as st
import pandas as pd
from ortools.sat.python import cp_model
import random
from datetime import datetime
import uuid
import subprocess
import pyarrow as pa
import logging
import os

Code Snippet:
When, I press the Generate button in the app:
if st.button(“Generate Lineup”):
model, lineup_vars = create_model(players, positions, skills)
st.session_state.lineup_df = solve_lineup_model(model, vars, players, skills, team_name)
st.session_state.lineup_generated = True,

Based on some debugging print lines, the app hangs during this function call:

Function to solve the model

def solve_lineup_model(model, vars, players, skills, team_name):
try:
st.markdown(‘

Starting to solve the model…
’, unsafe_allow_html=True)
solver = cp_model.CpSolver()
status = solver.Solve(model)
st.markdown(‘
Checking on the status…
’, unsafe_allow_html=True)
if status == cp_model.OPTIMAL or status == cp_model.FEASIBLE:
code continues…
The app never gets to display the print statement - Checking on the status…

Notes:

  • The issue seems to happen at the line status = solver.Solve(model), as the code never progresses beyond this point. However, since the same code/library runs in the deployed cloud app, it seems unlikely that the issue is related to the OR-Tools CP-SAT solver.
  • This function runs - and same entire python code - without issues on the Streamlit Cloud deployment via GitHub but fails locally now. Note that it used to run just fine locally a couple days ago with the same python code

Questions:

  1. Has anyone encountered a similar issue with Streamlit?
  2. Could this be related to local environment configuration or some underlying resource constraint?
  3. Any other suggestions or debugging steps I should consider?

I appreciate any insights or suggestions the community can provide.

2

Hi @Steven3 , did you identify the source of the issue here? I am experiencing the same issue. I’m new to streamlit and not sure where to dig.

3

Hi @Steven3,
I am running in the same error. The error also occurs when loading a model. My 2 cents is that I think Streamlit is getting overloaded with large files/models. I have attempted to use st.cache_resource decorators, but to no avail. If anyone has a solution, I’d love to hear it!

The code snippet breaking streamlit (1.28.2; upgrading the library didn’t work)
results = vector_store.similarity_search_by_vector(query_embedding, k=top_k)

update: after some fooling around, it turns out that my error was the result of faulty python code that persisted even when running outside of a streamlit environment.

4

I am running in the same error.

5

Good day. Thanks for everybody’s comments and feedback. It appears that this issue has occured with others too. Good news, is that I no longer have the “connect” issues that I had documented. The bad news, is that it was a few months ago and I don’t exactly remember the actions that I did in order to remedy the issue. I even reviewed my notes this am but nothing of importance. Today, the app properly runs on my local terminal and the Streamlit Community. Some users/coaches are already testing the app to see if it can help them too. If I recall, there was no major “aha” moment or comprehensive code redo. In fact, I think my solution at the time had more to with rebooting my local computer, restarting VS, and restarting Streamlit. I apologize for the very non-descript, non-technical recollection. I am not a programmer by trade and this project started with my need as a little league coach to have an app help me develop my team game lineups quickly, efficiently and effectively. Nonetheless, perhaps the underlying message is that the problem was indeed remedied. I hope everybody is able to fix their issues similarly and if anybody here has more illumination on their solutions, please provide any update for the benefit of the others. Thanks

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