111 Connection Refused on file upload - Flask / Nginx - nginx

Question

Looking for some insight into a problem I have been unable to solve, as I am inexperienced with server workings.
Main question: how can I see more detailed error information?
I have a web application that allows a user to upload a csv file; this csv is altered and returned to the user as a download. As it stands, this webapp worked just fine in my localhost development environment. As I try to use it on a separate server I have run into an issue when the file is uploaded. I am getting a 500 Internal Server Error (111 connection refused).
Since I am inexperienced, I don't know how to diagnose this error beyond checking error logs at /var/log/myapp-error.log
2018/10/04 09:24:53 [error] 24401#0: *286 connect() failed (111: Connection refused) while connecting to upstream, client: 128.172.245.174, server: _, request: "GET / HTTP/1.1", upstream: "http://[::1]:8000/", host: "ip addr here"
I would like to know how I can learn more about what is causing this error. I have set flask into debug mode but can't get a stack trace on that either. I will put some of the flask app and nginx configurations below in case that is helpful.
#app.route('/<path:filename>')
def get_download(filename):
return send_from_directory(UPLOAD_FOLDER, filename, as_attachment=True)
#app.route('/', methods = ['GET', 'POST'])
#app.route('/index', methods = ['GET', 'POST'])
def index():
path = os.path.join(dirname(realpath(__file__)), 'uploads')
uploaded = ''
if request.method == 'POST':
if 'file' not in request.files:
flash('no file part')
return redirect(request.url)
file = request.files['file']
if file.filename == '':
flash('no selected file')
return redirect(request.url)
if file and allowed_file(file.filename):
filename = secure_filename(file.filename)
file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
uploaded = str(path + '/' + filename)
df = preprocess_table(uploaded)
fp = classify(df, filename)
print(fp)
head, tail = os.path.split(fp)
print(tail)
get_download(tail)
return send_from_directory(UPLOAD_FOLDER, tail, as_attachment=True)
return render_template('index.html')
And here are my nginx settings.
server {
#listen on port 80 http
listen 80;
server_name _;
location / {
#redirect requests to same URL but https
return 301 https://$host$request_uri;
}
}
server {
#listen on port 443 https
listen 443 ssl;
server_name _;
#location of the self sign ssl cert
ssl_certificate /path/to/certs/cert.pem;
ssl_certificate_key /path/to/certs/key.pem;
#write access and error logs to /var/log
access_log /var/log/myapp_access.log;
error_log /var/log/myapp_error.log;
location / {
#forward application requests to the gunicorn server
proxy_pass http://localhost:8000;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
location /static {
#handle static files directly, without forwarding to the application
alias /path/to/static;
expires 30d;
}
}
Appreciate any insight/advice. Thank you!