How To Install Enketo On Ubuntu 16.04

Martijn van de Rijdt, 19 May 2015

This post describes how to setup a secure production server running Enketo for use with e.g. ODK Aggregate or KoBoCAT on DigitalOcean. It is meant to be a living document that will continuously improve. Use the forum to discuss any issues or suggestions for improvement, or if you’d like to expand it with instructions for other hosting providers.

Enketo Webform

1. Considerations

Installation is the easy part. Maintaining a reliable server with close to 0% downtime - especially when it becomes popular - is a whole lot harder. This document just provides a good starting point to launch a service, but does not help with running, troubleshooting and continuously updating a server. So before self-installing a production server, be prepared to spend a significant amount of time to run it afterwards.

Self-installation for most people is going to be far more expensive than using a public supported service, even if that service is not free. The time required to install and maintain a server and the “cost” of the likely longer periods of downtime will normally outweigh any fee you would pay for a provided service. If cost is the primary argument to self-install, it is probably not the right decision.

2. Create a public/private key pair

To authenticate with the server we are going to use a public key, because this is more secure than using (just) a password. Make sure you backup your private and public key combo, so that you do not lose access to your server when your computer breaks down.

If you’ve already created a public/private key pair for your computer you can skip this step.

OS X or Linux Users

Use the following command in the terminal in OS X or Linux:

ssh-keygen -t rsa

The location of the keys is ~/.ssh.

Windows Users

Download PuTTY.exe and PuTTYgen.exe. PuTTYgen is only required once, so can be run from the Downloads folder. PuTTY is a program you’d want to keep, so should be put in e.g. a newly created C:\Program Files\PuTTY folder and added to the Windows Start Menu.

Run PuTTYgen.exe and click Generate with the defaults (SSH-2 RSA, 2048 bits). Move the mouse as directed. Passphrase is optional. Save the private and public keys both (e.g. in My Documents\Keys). Make sure to use clear filenames (e.g. private_key.ppk and public_key.ppk). Copy the contents of the public key from the PuTTY Key Generator window to the clipboard with Ctrl-C.

Make a note of the location of the keys as you’ll need the keys soon. Also, make sure you have a backup of your keys!

More details:

More detailed instructions for OS X, Linux users can be found here (step 1 and 2 only) and for Windows users here (only the section: “Generating an SSH Key”).

3. Create a Server

For this tutorial, we are going to use Ubuntu 16.04 on a DigitalOcean server (aka a droplet). DigitalOcean provides the best bang for the buck when looking at CPU speed and CPU cores, both of which are the key criteria for Enketo Express performance. Their user interface is refreshingly well designed too. The tutorial should be quite similar for other VPS providers from section 4 onwards. If you do not have a DigitalOcean account yet, create one using this referral link to get a $10 credit.

Add your public key to your DigitalOcean account

In the DigitalOcean interface click on Your Settings and go to the security tab. Click on Add SSH Key and cut-and-paste your public key here. Do the same for any other users that will access your server.

Add SSH Key

Now, whenever you create a new server in DigitalOcean you can add any of these keys with the click of a button and will have immediate secure access via SSH, without a password!

When you buy a new computer you could just move your public and private key pair.

If multiple people/computers have (root) access to the server it is helpful to get the public key from all of them before you create your server, though you can also add them to your server later using a different method.

Create a Droplet

Click the Create Droplet button at the top of the screen to create your server.

  1. Give it a meaningful hostname, e.g. enketo-production
  2. Select a size. The $10/month option is fine to start with, but when traffic becomes meaningful you’ll probably quickly want to upgrade to the $20/month a plan because it has 2 CPU cores. Thankfully, upgrading can be done with the click of a button with only about 2-3 minutes downtime. The storage size is irrelevant for Enketo. When you upgrade you will have the (default) option to only upgrade RAM and CPU, or to upgrade storage size as well. It is usually best to choose the first because then you will be able to downgrade again later. You cannot downgrade to a droplet with less storage than you currently have. This allows you to easily try out different server sizes with little risk and little downtime. And because DigitalOcean bills per hour, the cost of trying out a different size is minimal too.
  3. Select a region that is closest to the geographical center of where your users are located.
  4. Select the Ubuntu 16.04 x64 image.
  5. Click on the SSH key(s) that may be used to access the server.
  6. Click Create and wait until this is finished.

Test: In your list of droplets you will now see an IP address that was assigned to your server (e.g. You should now be able to login to this server as root.

OS X and Linux users, try this out in the terminal with your assigned IP address as follows:

ssh root@

Windows users, try this out by opening PuTTY, adding the IP address as Host Name, clicking on SSH and Auth in the left Category tree, and adding the private key. For detailed instructions see this page. Select Yes when asked, and type root when asked. After verifying that this works, you can save your session so you won’t have to repeat these steps next time.

4. Server Installation

Login to your server as root via SSH if you haven’t done this already. You will probably never need to login as root again after this, because we are going to create a new user now (and will actually block root access during this process).

Create a user

In these examples we’ll create a user named enketo but you can use any other name. You will be prompted to enter a new password which you will need for configuring and updating your server (ie. for anything requiring sudo privileges). Note: All the terminal snippets below assume you chose enketo as username.

adduser enketo

To allow this user to login using your private key, we need to copy your public key (already added for root) to your new user account.

mkdir /home/enketo/.ssh
cp ~/.ssh/authorized_keys /home/enketo/.ssh
chown enketo:enketo /home/enketo/.ssh/authorized_keys
chmod 600 /home/enketo/.ssh/authorized_keys

To give this user sufficient privileges:

gpasswd -a enketo sudo

Configure ssh by disabling root access, and forcing public key authentication:

nano /etc/ssh/sshd_config

Scroll down with your keyboard arrow keys to find the existing settings and change their values to no as mentioned below. Remove the # in front of the sentence if present. These are the correct settings:

PermitRootLogin no
ChallengeResponseAuthentication no
PasswordAuthentication no
UsePAM no

Save your changes with CTRL+X, enter Y to confirm, and then hit Enter

Now restart the SSH service and exit:

service ssh restart

Test: You should now be able to login as enketo (instead of root) without being asked for a password and have sudo privileges with a password.

OS X and Linux users (change the IP address):

ssh enketo@

Windows users, do the same as before but enter user name enketo when asked.

Install required software

Login via ssh as the user you created previously (not as root). Install the first batch of software packages as follows and enter Y when asked to confirm:

sudo add-apt-repository -y ppa:chris-lea/redis-server
sudo apt-get update
sudo apt-get upgrade -y
sudo apt-get install -y git nginx htop build-essential redis-server checkinstall python

Install NodeJS and global Node packages

curl -sL | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g grunt-cli pm2

Let Ubuntu automatically install security updates (keep default values and select Yes when asked):

sudo dpkg-reconfigure -plow unattended-upgrades

5. Enketo Express Installation

Install Enketo Express and its dependencies. Warnings during the “npm install” step can be ignored. Errors should not be ignored.

cd ~
git clone
cd enketo-express
npm install --production

6. Configuration

Database configuration

Configure 2 redis instances that run on different ports:

sudo systemctl stop redis

sudo mv /etc/redis/redis.conf /etc/redis/redis-origin.conf
sudo cp ~/enketo-express/setup/redis/conf/redis-enketo-main.conf /etc/redis/
sudo cp ~/enketo-express/setup/redis/conf/redis-enketo-cache.conf /etc/redis/

sudo cp ~/enketo-express/setup/redis/systemd/system/* /etc/systemd/system/

Then, start the 2 redis instances:

sudo systemctl disable redis
sudo systemctl daemon-reload
sudo systemctl start redis@redis-enketo-main
sudo systemctl enable redis@redis-enketo-main
sudo systemctl start redis@redis-enketo-cache
sudo systemctl enable redis@redis-enketo-cache

Test: Cache database

redis-cli -p 6380

Test: Main database

redis-cli -p 6379

The response to both tests should be: “PONG”.

Note that configuring redis is pretty complex and Enketo’s sample configuration is not a one-size-fits-all solution. The size of the enketo-main database plays a big role in how you want to secure persistence. If enketo-main becomes too big, you’d probably want to switch to using both rdb and aof persistence. Read more here. It is also possible to use a 3rd-party redis service.

Enketo configuration

Create a configuration file by copying the default configuration:

cp ~/enketo-express/config/default-config.json ~/enketo-express/config/config.json
nano ~/enketo-express/config/config.json

The default configuration is almost functional. We just need to create a secret API key and encryption key. See this document for a detailed explanation of these configuration items. In this example we use a server at, but it is easiest to just set the server url to "" for now. So the minimum configuration items to change are:

    "linked form and data server": {
        "name": "My Aggregate",
        "server url": "",
        "api key": "EERTIUCJSHDGKHD234325",
    "encryption key": "a34sgfj324113413y",
    "less secure encryption key": "b542sdf32dabdery"

Use Ctrl-X and enter Y to save the configuration.


cd ~/enketo-express

The subsequent ‘Local Npm module “…” not found’ errors can be ignored as those modules are only used during development. Further configuration should be done in step 15.

7. Automatic Enketo Launch and Restart

Enketo Express should now be functional.

Test: Launch Enketo

cd ~/enketo-express
npm start

In your browser visit the IP address of the server, and add port 8005. E.g. visit You should see a page similar to the screenshot below.

Enketo Express front page

To make sure Enketo will run automatically upon reboot and will restart itself if it fails, we configure pm2. First stop the server with CTRL-C.

cd ~/enketo-express
pm2 start app.js -n enketo
pm2 save
sudo pm2 startup ubuntu -u enketo

Test: OS X and Linux users can test the API response, using the linked server url and corresponding api key for a non-existing form called test, by entering something like the following into a new terminal window:

curl --user EERTIUCJSHDGKHD234325: -d "server_url="

You should see a JSON response like this:

    "url": "",
    "code": 201

Test: To verify that Enketo starts automatically when the server reboots, you could reboot the server with:

sudo shutdown -r now

Then wait about 15 seconds and check that Enketo is running by visiting the URL in the browser as in the beginning of this section. Then SSH back into your server.

8. Domain setup

DNS Settings

If you have rented a domain name for your Enketo installation, we can configure the webserver. In this example we’ll be using a subdomain,, but you can also use the main domain.

First create a DNS entry for your domain using the tools that your DNS registrar provides. If you haven’t found a DNS registrar yet, you could use NameCheap. Create an A record that points to your IP address.

DNS example

NGINX Configuration

Create a webserver configuration as follows:

sudo nano /etc/nginx/sites-available/enketo

Use the following temporary configuration to test whether the domain and webserver are working:

server {
    listen 80;

    location / {
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;

Save the configuration with Ctrl-X and type Y.

Activate the new configuration:

sudo rm /etc/nginx/sites-enabled/default
sudo ln -s /etc/nginx/sites-available/enketo /etc/nginx/sites-enabled/enketo
sudo service nginx restart

Test: Go to your (sub)domain in the browser (e.g. You should be seeing the front page.

9. Install an SSL certificate

Nothing in this section is specific to Enketo. You can also use one of the thousands of SSL-certificate-installation-tuturials on the web.

Purchase an SSL certificate for your (sub)domain somewhere. This should not cost more than $10/year. You will be asked to provide a CSR. The recommended way of generating a CSR is to log in to your Enketo server and:

sudo mkdir /etc/nginx/ssl
sudo openssl genrsa -out /etc/nginx/ssl/enketo.key 2048
sudo openssl req -new -key /etc/nginx/ssl/enketo.key -out /etc/nginx/ssl/enketo.csr

Make sure to enter Country Name, State/Province, City/Locality, and Common Name. The Common Name is very important. In the example above the common name is

To display the content of the newly created CSR in order to copy and paste it:

sudo cat /etc/nginx/ssl/enketo.csr

Once you have received your SSL certificate bundle (or have created one from the various files that were sent), copy this enketo-bundle.crt to the server into /etc/nginx/ssl. Then change the permissions:

sudo chmod 600 /etc/nginx/ssl/enketo-bundle.crt

Create a DHE parameter: (This could easily take half an hour!)

cd /etc/nginx/ssl
sudo openssl dhparam -out dhparam.pem 4096

Update your webserver configuration:

sudo nano /etc/nginx/sites-available/enketo

The following configuration works well. Make sure to change to your domain and make sure the ssl certificate and key paths are correct. If you are going to iframe Enketo webforms into other web pages, you need to take out the line with X-Frame-Options DENY or change it.

server {
    listen       80;
    return 307 https://$server_name$request_uri;
server {
    listen 443;
    ssl on;
    ssl_certificate /etc/nginx/ssl/enketo-bundle.crt;
    ssl_certificate_key /etc/nginx/ssl/enketo.key;
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ssl_session_cache shared:SSL:10m;
    ssl_stapling on;
    ssl_stapling_verify on;
    resolver valid=300s;
    resolver_timeout 10s;
    ssl_prefer_server_ciphers on;
    ssl_dhparam /etc/nginx/ssl/dhparam.pem;
    client_max_body_size 100M;
    add_header Strict-Transport-Security max-age=63072000;
    add_header X-Frame-Options DENY; 
    add_header X-Content-Type-Options nosniff;
    location / {
        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 ;
        proxy_set_header X-Forwarded-Proto https ;

Restart the webserver and check if any errors are shown:

sudo service nginx restart

Test: Go to to test your SSL configuration. If all is done correctly you should get an A+.

SSL Labs result

10. Ban Rogue Users

Install fail2ban to reduce the disruption caused by bots continuously trying to break into your server:

sudo apt-get install -y fail2ban
sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local
sudo service fail2ban restart

You can optionally further tweak fail2ban by editing the configuration (sudo nano /etc/fail2ban/jail.local). Make sure to restart it after editing.

11. Firewall Setup

The following sets up a firewall:

sudo apt-get install ufw
sudo ufw allow ssh
sudo ufw allow 80
sudo ufw allow 443
sudo ufw enable
sudo ufw status

Type y when asked to proceed with operation.

Test: You should now no longer be able to access enketo in your browser using the server’s IP address and port.

12. Monitoring

A simple and very useful service to monitor uptime is E.g. use a HTTP(s) monitor for that checks every 5 minutes. Specify how you’d like to be alerted when your Enketo server is unresponsive.

UptimeRobot config

To add: monit and mmonit setup for advanced monitoring.

13. Backups

Only two files contain critical information that absolutely should be backed up: the main database and the Enketo configuration file.

The database file is located at /var/lib/redis/enketo-main.rdb. Restoring can be done simply by stopping redis (sudo systemctl stop redis@redis-enketo-main), copying the backup file, and starting redis (sudo systemctl start redis@redis-enketo-main).

The configuration file is located at ~/enketo-express/config/config.json. Restore this file by copying it and restarting Enketo.

Other files to perhaps consider backing up: NGINX configuration, custom scripts, other app configuration files.

14. Logging

You can log the unique instanceIDs of each successfully submitted record. This can be useful for troubleshooting your form/data server or Enketo.

  1. set log.submission to true in config/config.json
  2. create a logrotate.conf file (see sample in setup/config/logrotate.conf, you could cp this to the home directory e.g. and then modify it as required)
  3. setup cronjob for logrotate e.g. with 30 2 * * * /usr/sbin/logrotate /home/enketo/logrotate.conf -s /home/enketo/enketo-express/logs/logrotate

15. Final configuration

Once, you server and its integration with the form server is working, go through each item in this document to further configure your Enketo installation. Start by setting the server url to its proper value and see if the integration still works afterwards. Make sure to rebuild with grunt and pm2 restart enketo after updating your configuration.