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How to deploy

As there is a great diversity of operating systems, hosting environments, and WSGI servers, it is hard to provide universal and useful instructions for setting up KerkoApp for use in production.

You can expect a procedure similar to that of any Flask application, and there are many guides on the web covering this topic for various environments.

That said, you may refer to the guide below for step-by-step instructions. Even if your environment is different from the one this guide was designed for, it might provide you with some useful hints.

Deploying on Ubuntu 20.04 or 22.04 with nginx and gunicorn

These instructions will detail the steps and configurations required to get KerkoApp running on an Ubuntu 20.04 or 22.04 web server, using Gunicorn as the WSGI container and nginx as a HTTP proxy.

The procedure is similar that of any Flask application, but KerkoApp-specific steps are also covered here.

Install some required packages, including Python 3:

sudo apt install git nginx python3 python3-pip python3-venv

Create the user who will run the app:

sudo groupadd --system kerkoapp
sudo useradd --gid kerkoapp --shell /bin/bash --create-home --home-dir /home/kerkoapp --groups www-data kerkoapp

Switch to that user and clone the desired version of KerkoApp. If you want to use version 1.0.0, for example, replace VERSION in the command below with 1.0.0:

sudo su kerkoapp
git clone --branch VERSION ~/kerkoapp

Still as user kerkoapp, create a Python virtual environment and install the Python packages required by KerkoApp:

python3 -m venv ~/venv
source ~/venv/bin/activate
pip3 install -r ~/kerkoapp/requirements/run.txt
pip3 install gunicorn

Always as user kerkoapp, create the ~/.secrets.toml file. This is where you will put secret keys that should only be known to your server. Its content should look like the following:


You must set SECRET_KEY with a random string, and ZOTERO_API_KEY with an appropriate value (see configuration parameters).

Then create the ~/instance.toml file. This file will contain settings that are specific to your server, but are not secret. Its content should look like the following:


enabled = true
x_for = 1
x_proto = 1
x_host = 1
x_port = 0
x_prefix = 0

We are enabling the kerkoapp.proxy_fix parameters because we will configure nginx as a reverse proxy.

Then create the ~/config.toml file. This file will contain general settings for Kerko. You might have already tested KerkoApp on your desktop computer and created such file. If so, you could just copy that file to your server. At the very least it should contain the following settings:


title = "My Bibliography"

You must set ZOTERO_LIBRARY_ID and ZOTERO_LIBRARY_TYPE with appropriate values (see configuration parameters) so that Kerko can connect to your Zotero library.

It is not absolutely necessary to use three separate configuration files for KerkoApp as we just did. You could, for example, have just ~/instance.toml and put all of the settings there. However, it is a good practice to split the configuration, and that allows you to copy config.toml from or to other machines, or even share it with other people, without worrying about leaking secret keys or messing up your server-specific settings.

Once the configuration files are ready, Kerko should be able to talk to Zotero. Have Kerko retrieve your Zotero library's data by running the following command:

flask --debug kerko sync

The --debug switch is optional. If you use it, some messages will give you an better idea of the progress of the sync process. If you omit it, the command will run silently unless there are warnings or errors.

Depending on the size of your library, this process can complete within less than a minute or take an hour or more. Zotero throttles API requests to prevent its servers from getting overloaded, so sometimes the process might seem to freeze, but be patient and Kerko will resume synchronization a few minutes later.

Now that synchronization works, configure the cron task that will synchronize data from your Zotero library on a regular basis. Run the following command (always from the kerkoapp user):

crontab -e

That will launch the default nano editor. Add the following line at the very bottom, then save the file and exit the editor:

10 4 * * * cd /home/kerkoapp/kerkoapp && /home/kerkoapp/venv/bin/flask kerko sync

That will synchronize the data once a day, at 4:10am. You may specify a different time, of course.

Now exit from the kerkoapp user's shell, and go back to your usual sudoer account to finish the installation.

Configure a socket that will let Gunicorn to speak with nginx. As the superuser, create the /etc/systemd/system/kerkoapp.socket file, with the following content:

Description=KerkoApp socket



Configure a service that will run Gunicorn. As the superuser, create the /etc/systemd/system/kerkoapp.service file, with the following content:

Description=KerkoApp daemon

ExecStart=/home/kerkoapp/venv/bin/gunicorn wsgi:app --name kerkoapp --user kerkoapp --group www-data --workers 4 --log-level warning --error-logfile - --access-logfile - --bind unix:/run/kerkoapp.socket
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID


Reload the systemd configurations, then enable and start the new service by running the following commands:

sudo systemctl daemon-reload
sudo systemctl enable kerkoapp.socket
sudo systemctl enable kerkoapp.service
sudo systemctl start kerkoapp.socket

You can check whether the socket is active with this command:

sudo systemctl status kerkoapp.socket

If it shows up as 'active (listening)', you may now verify that it triggers the service:

curl --unix-socket /run/kerkoapp.socket localhost
sudo systemctl status kerkoapp.service

The curl command should output some HTML, and the systemctl command should now show the KerkoApp daemon as 'active (running)'.

If either the socket or the service doesn't work, you might want to check for errors in the log:

sudo journalctl --unit=kerkoapp

Once all of the above works, configure nginx to pass requests to Gunicorn. As the superuser, create the /etc/nginx/sites-available/kerkoapp.conf file with the following content, replacing with your actual domain name:

server {
    listen 80;

    location / {
        proxy_redirect off;
        proxy_set_header Host $http_host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Host $server_name;
        proxy_set_header X-Forwarded-Proto $scheme;

        if (!-f $request_filename) {
            proxy_pass http://unix:/run/kerkoapp.socket;

Enable the site by running the following command:

sudo ln -s /etc/nginx/sites-available/kerkoapp.conf /etc/nginx/sites-enabled/

Have nginx test the configuration:

sudo nginx -t

If the command reports the configuration test as successful, reload nginx to make the configuration changes effective:

sudo service nginx reload

You should now be able to view your KerkoApp site at!

The nginx configuration above will serve the application using the HTTP protocol. As for any website, HTTPS is strongly recommended. That will require that you install a SSL certificate and configure nginx to use it; that exercise is left to the reader.

Changing the configuration can be disruptive

Making any change to a configuration file requires that you at least restart the application afterwards for the change to become effective.

Moreover, some parameters have an effect on the structure of the cache or the search index that Kerko depends on. Changing this kind of parameter may require that you rebuild either. Refer to the documentation of the parameter to check if specific actions need to be taken after a change.

The commands below, for example, will allow you to clean and rebuild the search index, and to restart KerkoApp:

sudo -iu kerkoapp bash -c 'cd /home/kerkoapp/kerkoapp && /home/kerkoapp/venv/bin/flask kerko clean index'
sudo -iu kerkoapp bash -c 'cd /home/kerkoapp/kerkoapp && /home/kerkoapp/venv/bin/flask kerko sync'
sudo systemctl stop kerkoapp.socket
sudo systemctl start kerkoapp.socket

Submitting your sitemap to search engines

Kerko generates an XML Sitemap that can help search engines discover your bibliographic records.

The path of the sitemap is BASE_URL/sitemap.xml, where BASE_URL should be replaced with the protocol, domain, port, and Kerko URL path prefix that are relevant to your installation, e.g.,

Different search engines may have different procedures for submitting sitemaps (Google, Bing, Yandex).

However, a standard method consists in adding a Sitemap directive to a robots.txt file served at the root of your site, to tell web crawlers where to find your sitemap. For example, one might add the following line to robots.txt:


A robots.txt file can have multiple Sitemap directives, thus the Kerko sitemap can be specified alongside any other sitemaps you might already have.