Server Back End for Android app (ktor-note-app )

Technology used

Deploy Instructions / Helpful commands

For SSL/HTTPS traffic.

Set up the server folder structure locally. From root folder:

 take root # create the `/root` folder locally (not used on the server)
 take home
 take keys
 keytool -genkey -v -keystore ktornoteapp.jks -alias ktor_note_app -keyalg RSA -keysize 4096
 -> password: <**ENTER_KEYSTORE_PASSWORD***> <-- keyStorePassword
 -> first and lastname: chris athanas
 -> organization unit: realityexpander
 -> organization: realityexpander
 -> city: austin
 -> state: texas
 -> country code: us
 -> correct: yes
 -> enter key password: <**PRIVATE_KEY_PASSWORD_NOT_NECESSARY**> <-- privateKeyPassword (may be same as keystore password)
 -> enter key password again: <**PRIVATE_KEY_PASSWORD_NOT_NECESSARY**>

For LOGIN to server.

Generate SSH keys:

 ssh-keygen -t rsa -m PEM
 Enter file in which to save the key (/Users/chrisathanas/.ssh/id_rsa):
 # Enter this (the location to save the .ssh key file):
 /Users/chrisathanas/.ssh/hostinger_rsa
 # Press enter twice (no passphrase needed)
 Your public key has been saved in /Users/chrisathanas/.ssh/hostinger_rsa.pub
 cat /Users/chrisathanas/.ssh/hostinger_rsa.pub # This is the public key. We need to copy the private (non-.pub) to the server.
 ssh-copy-id -i /Users/chrisathanas/.ssh/hostinger_rsa root@<server-ip> # copy the private key to the server (must use password to login)
 ssh -i /Users/chrisathanas/.ssh/hostinger_rsa root@<server-ip> # connect to the server using the private key
 To SSH into the server without long reference to `.../.ssh/hostinger_rsa`, do the following:
 nano ~/.ssh/config # & Add these lines: (to allow ssh/scp/sftp to work without supplying password)
 Host <shortcut-name>
 Host <server-ip-address>
 User root
 IdentityFile ~/.ssh/hostinger_rsa

Secure FTP (sftp) commands:

 Put folders recursively:
 put -R *
 Tree (tree) commands:
 tree -phD = show all files and folders in the current directory with -la and human-readable size & Date Modified
 tree -saD = show hidden files & dates
 How to create an SSH shortcut
 https://www.digitalocean.com/community/tutorials/how-to-create-an-ssh-shortcut
 Local dir structure (mirrored on the server):
 root # this is the same as root folder on the server
 home
 keys
 ktornoteapp.jks # keystore for the server app, allows for https traffic (self-signed)
 release
 app-0.X.X.jar
 startApp.sh

Deploy to an Ubuntu 20.04 (Focal) server: (also works with Ubuntu 18.04.6 LTS (GNU/Linux 4.15.0 x86_64))

 From root of project, create the FatJar file of our app:
 ./gradle jar
 Run sftp to upload the jar of the app to the server:
 sftp root@<ip address of server>
 --> enter <server_password>
 mkdir home
 cd home
 put app-0.0.1.jar
 Make a new tab in the terminal, to upload the keys to the server:
 cd keys
 sftp root@<ip address of server>:/home
 --> enter <server_password>
 mkdir keys
 cd keys
 put ktornoteapp.jks
 Install the app and mongo on our server:
 Make a new tab in the terminal.
 ssh root@<ip address of server>
 --> enter <server_password>
 sudo apt-get update
 cd /home
 ls
 Should see our files
 sudo apt-get install openjdk-8-jdk
 --> Press enter to install java
 java -version

Install community edition of MongoDB:

 https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-ubuntu/
 // wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -
 wget -qO - https://www.mongodb.org/static/pgp/server-5.0.asc | sudo apt-key add -
 Reload the package database:
 sudo apt-get update
 Install the MongoDB packages:
 sudo apt-get install -y mongodb-org
 Start the MongoDB service:
 sudo systemctl start mongod
 sudo systemctl status mongod
 Install nano editor:
 sudo apt-get install -y nano
 Create service configuration file for our app:
 sudo nano /etc/systemd/system/ktornoteapp.service
 [Unit]
 Description=Ktor Note App service
 After=mongod.service // defines which service to start after
 StartLimitIntervalSec=0 // prevents the service from not being started if it fails to start more than 5 times
 [Service]
 Type=simple
 RestartSec=5 // how long to wait before restarting the service
 Restart=always // restart the service if it fails to start
 User=root // run the service as root user
 ExecStart=/root/home/release/startApp.sh // good shortcut for absolute path
 // ExecStart=/usr/bin/java -jar /root/home/release/app-0.0.1.jar // run an app of a specific version (** -> dont add this commented line)
 [Install]
 WantedBy=multi-user.target
 ^s^x // Save and Exit
 Start the service:
 sudo systemctl start ktornoteapp // start the service
 sudo systemctl restart ktornoteapp // start the service
 sudo systemctl status ktornoteapp // check if the service is running & show logs, 'q' to quit
 sudo systemctl enable ktornoteapp // enable the service to start at boot time

Show the logs & follow updates:

 journalctl -f -u ktornoteapp
 Show the last 50 lines & follow updates:
 tail -n 50 -f /var/log/syslog
 or:
 journalctl -f -u ktornoteapp -n 50
 Clear the logs from all but last 2 days:
 journalctl --vacuum-time=2d
 more options:
 journalctl -u ktornoteapp.service // -f to show logs from the last 24 hours, 'q' to quit
 journalctl -u ktornoteapp.service | grep -i error // grep for errors
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 // show the last 10 errors
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 | less // show the last 10 errors in a less window
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 | less -R // show the last 10 errors in a less window, with readline support
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 | less -R -S // show the last 10 errors in a less window, with readline support and scrollback
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 | less -R -S -X // show the last 10 errors in a less window, with readline support and scrollback and exit on 'q'
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 | less -R -S -X -M // show the last 10 errors in a less window, with readline support and scrollback and exit on 'q' and show the cursor at the end of the file
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 | less -R -S -X -M -F // show the last 10 errors in a less window, with readline support and scrollback and exit on 'q' and show the cursor at the end of the file and follow the logs
 journalctl -u ktornoteapp.service | grep -i error | tail -n 10 | less -R -S -X -M -F -N // show the last 10 errors in a less window, with readline support and scrollback and exit on 'q' and show the cursor at the end of the file and follow the logs and dont show the cursor
 to set the max size of the logs for the system:
 sudo nano /etc/systemd/journald.conf
 [Journal]
 SystemMaxUse=50M
 ^s^x

Disable firewall:

 sudo apt-get install ufw
 Get status of firewall:
 sudo ufw status
 Disable firewall:
 sudo ufw disable
 Enable firewall:
 sudo ufw enable
 Allow incoming connections:
 sudo ufw allow <port> // 8002 for our app
 Allow outgoing connections:
 sudo ufw allow out <port> // 8002 for our app
 Allow incoming connections from a specific IP:
 sudo ufw allow from <ip>
 Allow outgoing connections to a specific IP:
 sudo ufw allow out from <ip>
 Allow incoming connections from a specific IP and port:
 sudo ufw allow from <ip> port <port>
 Allow outgoing connections to a specific IP and port:
 sudo ufw allow out to <ip> port <port>

Check ip ports in use:

 sudo netstat -peanut | grep ":8001" # just look for port 8001
 sudo lsof -i :27017
 sudo lsof -i :8001
 sudo lsof -i :8002

Get command that started a particular process:

 ps -fp <PID>

Get PID of a command that started processes:

 ps -ef | grep java | grep -v grep

Add Traffic to and from mongod instances:

 iptables -A INPUT -s <ip-address> -p tcp --destination-port 27017 -m state --state NEW,ESTABLISHED -j ACCEPT
 iptables -A OUTPUT -d <ip-address> -p tcp --source-port 27017 -m state --state ESTABLISHED -j ACCEPT

Remove traffic from mongod instances:

 iptables -L --line-numbers # lists both INPUT and OUTPUT
 iptables -D INPUT <line-number-to-remove>

Issues with connecting to mongodb:

 https://www.mongodb.com/docs/compass/current/troubleshooting/connection-errors/
 https://www.mongodb.com/docs/manual/reference/configuration-options/#mongodb-setting-net.bindIp

To allow external access by MongoDB Compass to your server:

 Update the /etc/mongod.conf YAML file to allow external access:
 sudo nano /etc/mongod.conf
 # network interfaces
 net:
 port: 27017
 bindIp: 127.0.0.1, <your-server-ip-address>
 security:
 authorization: enabled

Restart the MongoDB service:

 sudo systemctl restart mongod

Log in to remote service with Mongo Compass:

 New connection:
 Select <Advanced Options> twirl-down
 Select the <Proxy/SSH> tab
 Click the "SSH with Password" button
 Enter the following:
 SSH Hostname: <your-server-ip-address>
 SSH Port: 22
 SSH Username: <your-SSH-username> // usually 'root'
 SSH Password: <your-SSH-password> // <your-SSH-password>
 Select the "Authentication" tab
 Enter the following:
 Username: <your-admin-username> // usually 'theAdmin'
 Password: <your-admin-password> // <your-admin-password>
 Authentication Database: admin // usually 'admin'
 Authentication Mechanism: Default // usually 'Default'

Monitor IP traffic in real time: https://linuxize.com/post/linux-watch-command/

 watch -d --interval 0 'iptables -nvL | grep -v "0 0"'
 watch -d=cumulative # Keep highlighting values that have changed

To remove the server warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8):

 locale-gen en_US.utf8

Kill a user session: (log the user out)

 sudo pkill -u <username>

Build commands

 Build and upload app to server:
 ./gradle buildAndUploadLatestReleaseWithKeys
 Build jar only:
 ./gradle jar
 Show app manifest:
 ./gradle getAppManifest

GOTTA BE CAREFUL WITH THE KEYS! Make sure you never check in your *.jks file to GitHub!

ALSO give your mongoDb a password!

 All your data is a backed up. You must pay 0.043 BTC to 1Kz6v4B5CawcnL8jrUvHsvzQv5Yq4fbsSv
 48 hours for recover it. After 48 hours expiration we will leaked and exposed all your data.
 In case of refusal to pay, we will contact the General Data Protection Regulation, GDPR and
 notify them that you store user data in an open form and is not safe. Under the rules of the law,
 you face a heavy fine or arrest and your base dump will be dropped from our server!
 You can buy bitcoin here, does not take much time to buy https://localbitcoins.com or
 https://buy.moonpay.io/ After paying write to me in the mail with your DB
 IP: recmydb+1t55h@onionmail.org and/or mariadb@mailnesia.com and you will receive a
 link to download your database dump.

Web url to get all notes for a specific user:

 http://localhost:8001/getAllNotesForEmail?email=test123@123.com

MongoDB commands:

help ;show help
show dbs ;show database names
show collections ;show collections in current database
show users ;show users in current database
show profile ;show most recent system.profile entries with time >= 1ms
use <db name> ;set curent database to <db name>
db.addUser (username, password)
db.removeUser(username)
db.cloneDatabase(fromhost)
db.copyDatabase(fromdb, todb, fromhost)
db.createCollection(name, { size : ..., capped : ..., max : ... } )
db.getName()
db.printCollectionStats()
db.currentOp() ;displays the current operation in the db
db.getProfilingLevel()
db.setProfilingLevel(level) ;0=off 1=slow 2=all
db.getReplicationInfo()
db.printReplicationInfo()
db.printSlaveReplicationInfo()
db.repairDatabase()
db.version() ;current version of the server

Create an admin user:

 use admin
 db.createUser({user: "theAdmin", pwd: "password", roles: [{role: "readWrite", db: "admin"}]})
or:
 db.createUser({user: "theAdmin", pwd: passwordPrompt(),
 roles: [
 { role: "userAdminAnyDatabase", db: "admin" },
 { role: "readWriteAnyDatabase", db: "admin" }
 ]})
Auth the user:
 use admin
 db.auth("theAdmin", passwordPrompt()) // or cleartext password
Show users:
 use admin
 db.system.users.find()
Remove user:
 use admin
 db.system.users.deleteOne({user: "user"})