open-notebook/docs/6-TROUBLESHOOTING/connection-issues.md

Connection Issues - Network & API Problems

Frontend can't reach API or services won't communicate.

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"Cannot connect to server" (Most Common)

What it looks like:

• Browser shows error page
• "Unable to reach API"
• "Cannot connect to server"
• UI loads but can't create notebooks

Diagnosis:

# Check if API is running
docker ps | grep api
# Should see "api" service running

# Check if API is responding
curl http://localhost:5055/health
# Should show: {"status":"ok"}

# Check if frontend is running
docker ps | grep frontend
# Should see "frontend" or React service running

Solutions:

Solution 1: API Not Running

# Start API
docker compose up api -d

# Wait 5 seconds
sleep 5

# Verify it's running
docker compose logs api | tail -20

Solution 2: Port Not Exposed

# Check docker-compose.yml has port mapping:
# api:
#   ports:
#     - "5055:5055"

# If missing, add it and restart:
docker compose down
docker compose up -d

Solution 3: API_URL Mismatch

# In .env, check API_URL:
cat .env | grep API_URL

# Should match your frontend URL:
# Frontend: http://localhost:8502
# API_URL: http://localhost:5055

# If wrong, fix it:
# API_URL=http://localhost:5055
# Then restart:
docker compose restart frontend

Solution 4: Firewall Blocking

# Verify port 5055 is accessible
netstat -tlnp | grep 5055
# Should show port listening

# If on different machine, try:
# Instead of localhost, use your IP:
API_URL=http://192.168.1.100:5055

Solution 5: Services Not Started

# Restart everything
docker compose restart

# Wait 10 seconds
sleep 10

# Check all services
docker compose ps
# All should show "Up"

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Connection Refused

What it looks like:

Connection refused
ECONNREFUSED
Error: socket hang up

Diagnosis:

• API port (5055) not open
• API crashed
• Wrong IP/hostname

Solution:

# Step 1: Check if API is running
docker ps | grep api

# Step 2: Check if port is listening
lsof -i :5055
# or
netstat -tlnp | grep 5055

# Step 3: Check API logs
docker compose logs api | tail -30
# Look for errors

# Step 4: Restart API
docker compose restart api
docker compose logs api | grep -i "error"

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Timeout / Slow Connection

What it looks like:

• Page loads slowly
• Request times out
• "Gateway timeout" error

Causes:

• API is overloaded
• Network is slow
• Reverse proxy issue

Solutions:

Check API Performance

# See CPU/memory usage
docker stats

# Check logs for slow operations
docker compose logs api | grep "slow\|timeout"

Reduce Load

# In .env:
SURREAL_COMMANDS_MAX_TASKS=2
API_CLIENT_TIMEOUT=600

# Restart
docker compose restart

Check Network

# Test latency
ping localhost

# Test API directly
time curl http://localhost:5055/health

# Should be < 100ms

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502 Bad Gateway (Reverse Proxy)

What it looks like:

502 Bad Gateway
The server is temporarily unable to service the request

Cause: Reverse proxy can't reach API

Solutions:

Check Backend is Running

# From the reverse proxy server
curl http://localhost:5055/health

# Should work

Check Reverse Proxy Config

# Nginx example (correct):
location /api {
    proxy_pass http://localhost:5055/api;
    proxy_http_version 1.1;
}

# Common mistake (wrong):
location /api {
    proxy_pass http://localhost:5055;  # Missing /api
}

Set API_URL for HTTPS

# In .env:
API_URL=https://yourdomain.com

# Restart
docker compose restart

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Intermittent Disconnects

What it looks like:

• Works sometimes, fails other times
• Sporadic "cannot connect" errors
• Works then stops working

Cause: Transient network issue or database conflicts

Solutions:

Enable Retry Logic

# In .env:
SURREAL_COMMANDS_RETRY_ENABLED=true
SURREAL_COMMANDS_RETRY_MAX_ATTEMPTS=5
SURREAL_COMMANDS_RETRY_WAIT_STRATEGY=exponential_jitter

# Restart
docker compose restart

Reduce Concurrency

# In .env:
SURREAL_COMMANDS_MAX_TASKS=2

# Restart
docker compose restart

Check Network Stability

# Monitor connection
ping google.com

# Long-running test
ping -c 100 google.com | grep "packet loss"
# Should be 0% loss

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Different Machine / Remote Access

You want to access Open Notebook from another computer

Solution:

Step 1: Get Your Machine IP

# On the server running Open Notebook:
ifconfig | grep "inet "
# or
hostname -I
# Note the IP (e.g., 192.168.1.100)

Step 2: Update API_URL

# In .env:
API_URL=http://192.168.1.100:5055

# Restart
docker compose restart

Step 3: Access from Other Machine

# In browser on other machine:
http://192.168.1.100:8502
# (or your server IP)

Step 4: Verify Port is Exposed

# On server:
docker compose ps

# Should show port mapping:
# 0.0.0.0:8502->8502/tcp
# 0.0.0.0:5055->5055/tcp

If Still Doesn't Work

# Check firewall on server
sudo ufw status
# May need to open ports:
sudo ufw allow 8502
sudo ufw allow 5055

# Check on different machine:
telnet 192.168.1.100 5055
# Should connect

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CORS Error (Browser Console)

What it looks like:

Cross-Origin Request Blocked
Access-Control-Allow-Origin

In browser console (F12):

CORS policy: Response to preflight request doesn't pass access control check

Cause: Frontend and API URLs don't match

Solution:

# Check browser console error for what URLs are being used
# The error shows:
# - Requesting from: http://localhost:8502
# - Trying to reach: http://localhost:5055

# Make sure API_URL matches:
API_URL=http://localhost:5055

# And protocol matches (http/https)
# Restart
docker compose restart frontend

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Testing Connection

Full diagnostic:

# 1. Services running?
docker compose ps
# All should show "Up"

# 2. Ports listening?
netstat -tlnp | grep -E "8502|5055|8000"

# 3. API responding?
curl http://localhost:5055/health

# 4. Frontend accessible?
curl http://localhost:8502 | head

# 5. Network OK?
ping google.com

# 6. No firewall?
sudo ufw status | grep -E "5055|8502|8000"

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Checklist for Remote Access

• Server IP noted (e.g., 192.168.1.100)
• Ports 8502, 5055, 8000 exposed in docker-compose
• API_URL set to server IP
• Firewall allows ports 8502, 5055, 8000
• Can reach server from client machine (ping IP)
• All services running (docker compose ps)
• Can curl API from client (curl http://IP:5055/health)

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SSL Certificate Errors

What it looks like:

[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed
Connection error when using HTTPS endpoints
Works with HTTP but fails with HTTPS

Cause: Self-signed certificates not trusted by Python's SSL verification

Solutions:

Solution 1: Use Custom CA Bundle (Recommended)

# In .env:
ESPERANTO_SSL_CA_BUNDLE=/path/to/your/ca-bundle.pem

# For Docker, mount the certificate:
# In docker-compose.yml:
volumes:
  - /path/to/your/ca-bundle.pem:/certs/ca-bundle.pem:ro
environment:
  - ESPERANTO_SSL_CA_BUNDLE=/certs/ca-bundle.pem

Solution 2: Disable SSL Verification (Development Only)

# WARNING: Only use in trusted development environments
# In .env:
ESPERANTO_SSL_VERIFY=false

Solution 3: Use HTTP Instead

If services are on a trusted local network, HTTP is acceptable:

Change the base URL in your credential (Settings → API Keys) from https:// to http://
Example: http://localhost:1234/v1

Security Note: Disabling SSL verification exposes you to man-in-the-middle attacks. Always prefer custom CA bundle or HTTP on trusted networks.

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Still Having Issues?

• Check Quick Fixes
• Check FAQ
• Check logs: docker compose logs
• Try restart: docker compose restart
• Check firewall: sudo ufw status
• Ask for help on Discord