DEV Community: NT

Leaving DEV.to due to a bug

NT — Sat, 20 Jan 2024 18:35:30 +0000

I'm leaving DEV.to because of a bug that is intolerable.
This bug was reported at least a year ago, but not addressed.
There are 3 reports so far I could find.
https://github.com/forem/forem/issues/18939
https://github.com/forem/forem/issues/15208
https://github.com/forem/forem/issues/20469

Wishing DEV.to and forem team to address it for others who are using this site.

See me at my GitHub Page

AWS Lightsail Java Server Setup Memo

NT — Mon, 15 Jan 2024 16:54:35 +0000

This is a journal of my setup for a Java server on AWS, Lightsail in particular for my Sump Water Level Application project.

Applications

OS: Amazon Linux 2023
Reverse Proxy: Nginx
Application: Spring Boot jar - as Java server
DB: MySQL
Cache: Redis
Streamlit - Presentation of the Sump Water Level data

Why Lightsail

Because this server is for a purpose of showcasing the Spring Boot application, the load is very light, almost nil. One VPS suffices hosting Nginx, MySQL and Redis. For a real-world application, with somewhat mild workload, I'd use separate AWS services, such as RDS for MySQL and ElastiCache for Redis.

Setup Steps

1. Select Amazon Linux 2023 from the "Create Instance" page.

I didn't choose Nginx instance because it's a Bitnami package with PHP, Memcache, and other frills I don't need. I chose 1GB RAM plan (the cheapest, $5/mo) to start with. Since it'll connect with just 1 Raspberry Pi and the Web UI will be basically only for 1 user (me), this should be sufficient.

Note: Below in screenshot, I started with 512MB instance. But I moved it to 1GB instance.

In moving the instance from 512MB to 1G, I created a snapshot of 512MB instance, and created a new instance from it.
Somehow, the new instance doesn't have a swap file (probably because the memory size is different), I created it manually.

 dd if=/dev/zero of=/swapfile bs=1M count=1024
 chmod 600 /swapfile
 mkswap /swapfile
 swapon /swapfile
 swapon -s
 free

Then, edited /etc/fstab and added the line on the bottom so that swap file will be used after reboot.

/swapfile swap swap defaults 0 0

2. Set up the basics

Attach Static IP
Add SSH public key from my laptop
Give a host name to the IP locally (/etc/hosts) - I named it sumpserver.

$ ssh ec2-user@sumpserver   
The authenticity of host 'sumpserver (xx.xx.xx.xx)' can't be established.
ED25519 key fingerprint is SHA256:abdcABCD1234...
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'sumpserver' (ED25519) to the list of known hosts.
   ,     #_
   ~\_  ####_        Amazon Linux 2023
  ~~  \_#####\
  ~~     \###|
  ~~       \#/ ___   https://aws.amazon.com/linux/amazon-linux-2023
   ~~       V~' '->
    ~~~         /
      ~~._.   _/
         _/ _/
       _/m/'
[ec2-user@ip-xx-xx-xx-xxx ~]$

Set the time zone. Add below in .bash_profile

TZ='America/New_York'; export TZ

Edit prompt

export PS1='\[\e[1;106m\]\u \W\[\e[m\] $ '

3. Install MySQL

sudo su
dnf upgrade
dnf localinstall -y https://dev.mysql.com/get/mysql80-community-release-el9-1.noarch.rpm
dnf install -y mysql mysql-server mysql-community-client
systemctl start mysqld.service
systemctl status mysqld.service
systemctl enable mysqld.service

Check root temporary password

grep 'temporary password' /var/log/mysqld.log

mysql -u root -p

Create user and database

ALTER USER 'root'@'localhost' IDENTIFIED BY '<myrootpassword_here>';
CREATE USER 'sumpadmin'@'%' identified by '<sumpserver_user_password>';
CREATE DATABASE sumpdata;
GRANT ALL PRIVILEGES ON sumpdata.* TO 'sumpadmin'@'%';

4. Install Nginx

Installation of Nginx itself is straightforward.

sudo su
dnf -y update
dnf list --available nginx
dnf -y install nginx
nginx -v
systemctl start nginx.service
systemctl status nginx.service
systemctl enable nginx.service
curl http://localhost

Point your browser to the public IP to check it's accessible from the internet.

Let's Encrypt Certificate

At this point, it only supports non-secure HTTP only. For HTTPS, I did the following.

Obtain a domain and associate with AWS IP.

Install Certbot
Certbot is a CLI that helps to obtain and maintain Let's Encrypt cert.

sudo su
dnf install certbot python3-certbot-nginx -y
certbot --version

Before asking the certbot to obtain a SSL cert, configure Nginx server setting for the domain, so that certbot can edit the config for the matching domain.

/etc/nginx/conf.d/sumpdata.conf

server {
    listen       80;
    listen  [::]:80;
    server_name  sumpdata.nobudev7.com;


    location / {
        root   /usr/share/nginx/html;
        index  index.html index.htm;
    }
}

# Test the conf file
nginx -t
# Reload the conf
nginx -s reload

Run Certbot
Now, run certbot to obtain an SSL cert for the domain.

certbot --nginx -d sumpdata.nobudev7.com

After successfully obtained and installed the cert to Nginx configuration, the above created sumpdata.conf was edited by Certbot as follows.

server {
    server_name  sumpdata.nobudev7.com;


    location / {
        root   /usr/share/nginx/html;
        index  index.html index.htm;
    }

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/sumpdata.nobudev7.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/sumpdata.nobudev7.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}
server {
    if ($host = sumpdata.nobudev7.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    listen       80;
    listen  [::]:80;
    server_name  sumpdata.nobudev7.com;
    return 404; # managed by Certbot


}

Notice that Certbot made non-secure HTTP (port 80) to automatically redirect to HTTPS.

Configure Auto Renew
During the above process, certbot output the following.

Certbot has set up a scheduled task to automatically renew this certificate in the background.

However, checking timers revealed that nothing is set up for certbot.

systemctl list-timers

After reading various posts, I figured that certbot timer name is certbot-renew.timer not certbot.timer as widely referenced. Even Certbot itself might have a bug in setting the timer. Below, I set up the timer manually.

# Where is the certbot timer and service?
ls /lib/systemd/system/certbot*
/lib/systemd/system/certbot-renew.service
/lib/systemd/system/certbot-renew.timer

Try to see if the service works, and check the status.

systemctl start certbot-renew.service
systemctl status certbot-renew.service

Output

○ certbot-renew.service - This service automatically renews any certbot certificates found
     Loaded: loaded (/usr/lib/systemd/system/certbot-renew.service; static)
     Active: inactive (dead) since Mon 2024-01-15 12:57:33 EST; 31s ago
TriggeredBy: ○ certbot-renew.timer
    Process: 69039 ExecStart=/usr/bin/certbot renew --noninteractive --no-random-sleep-on-renew $PRE_HOOK $POST_HOOK $RENEW_HOOK $DEPLOY_HOOK $CERTBOT_ARGS (code=exited, status=0/SUCCESS)
   Main PID: 69039 (code=exited, status=0/SUCCESS)
        CPU: 500ms

Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]: Processing /etc/letsencrypt/renewal/sumpdata.nobudev7.com.conf
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]: Certificate not yet due for renewal
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]: The following certificates are not due for renewal yet:
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]:   /etc/letsencrypt/live/sumpdata.nobudev7.com/fullchain.pem expires on 2024-04-14 (skipped)
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]: No renewals were attempted.
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal certbot[69039]: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal systemd[1]: certbot-renew.service: Deactivated successfully.
Jan 15 12:57:33 ip-xx-xx-xx-xx.ec2.internal systemd[1]: Finished certbot-renew.service - This service automatically renews any certbot certificates found.

Start the timer

systemctl start certbot-renew.timer
# Check if it's scheduled.
systemctl list-timers certbot-renew.timer
# OUTPUT
NEXT                        LEFT     LAST PASSED UNIT                ACTIVATES
Tue 2024-01-16 06:58:43 EST 16h left -    -      certbot-renew.timer certbot-renew.service

Note: Amazon Linux 2023 doesn't come with crontab.

5. Install Git

sudo su
dnf install git -y
# exit to ec2-user
exit
git --version

6. Install Redis

dnf list --available |grep redis
# OUTPUT
redis6.x86_64         6.2.13-1.amzn2023.0.1    amazonlinux
redis6-devel.x86_64   6.2.13-1.amzn2023.0.1    amazonlinux
redis6-doc.noarch     6.2.13-1.amzn2023.0.1    amazonlinux

dnf install redis6 -y
systemctl start redis6
systemctl status redis6
systemctl enable redis6
redis6-cli 
# OUTPUT
127.0.0.1:6379>

7. Install Java (Runtime)

# Check Java availability
dnf list --available java-21-amazon-corretto
# Install
dnf install java-21-amazon-corretto -y
java --version

8. Deploy Jar file from Git

The Git Action (discussed in GitHub Actions for Jar file deployment) build a jar file from the Java project.
While the intention is to download it manually, I put all commands in a shell script.

#!/bin/bash

# Remove files named sumpdata*.jar
rm -f sumpdata*.jar

latestjar=$(curl \
    -s https://api.github.com/repos/nobudev7/sumpdata/actions/artifacts \
    | jq -r '.artifacts | max_by(.created_at) | .archive_download_url'
)

echo "Downloading $latestjar..."

curl -L -o artifact.zip\
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer <github_token>" \
  -H "X-GitHub-Api-Version: 2022-11-28" "$latestjar"

if [ $? -eq 0 ]; then
  unzip artifact.zip
  rm artifact.zip
else
  echo "Downloading Jar failed: $latestjar"
fi

9. Run Jar application

To test if the Jar application properly work, start it with proper variables. In my case, I have different MySQL user/pass than what's in the application.properties file, I pass it via environment variables (can be Dxxx=yyy param as well).

SPRING_DATASOURCE_USERNAME=<mysql_user> SPRING_DATASOURCE_PASSWORD=s<mysql_pass> java -jar sumpdata-0.2.0.jar

Add an entry from the local instance for testing.

curl -X POST 'http://localhost:8080/devices/2/entries?measuredOn=2023-10-24T16:37:06&value=12.2' -H 'Content-Type: text/plain'

Check the MySQL table.

mysql> select * from data_entry;
+----------+----------------------------+-------+
| deviceid | measured_on                | value |
+----------+----------------------------+-------+
|        2 | 2023-10-24 16:37:06.000000 |   122 |
+----------+----------------------------+-------+
1 row in set (0.00 sec)

9. Run a Jar app as a service

It seems that the current way of setting up a service is to use systemctl edit <service_name>.
However, if you run it the first time, on Amazon Linux 2023, it shows an error and suggests --force option.

# systemctl edit sumpdata
No files found for sumpdata.service.
Run 'systemctl edit --force --full sumpdata.service' to create a new unit.

Running it as suggested, an editor (nano) shows up. This will become the service file.

[Unit]
Description=Samp Data service
After=syslog.target network.target

[Service]
SuccessExitStatus=143

User=ec2-user
Group=ec2-user

Type=simple

WorkingDirectory=/home/ec2-user/sumpdata
ExecStart=/usr/bin/java -jar sumpdata.jar
ExecStop=/bin/kill -15 $MAINPID

[Install]
WantedBy=multi-user.target

Save the file, but don't change the file name, as the file name is temporary and the systemctl will properly move it to /etc/systemd/system.

Note that, the above service file doesn't have any Environment values. That is to be written under override.conf, by systemctl edit <service_name>.

The same (nano) editor opens up, and between comment lines, add the env variables.

### Editing /etc/systemd/system/sumpdata.service.d/override.conf
### Anything between here and the comment below will become the new contents of the file

[Service]
Environment="SPRING_DATASOURCE_USERNAME=dbuser"
Environment="SPRING_DATASOURCE_PASSWORD=dbpassword"

### Lines below this comment will be discarded

### /etc/systemd/system/sumpdata.service
# [Unit]
# Description=Samp Data service
# After=syslog.target network.target
...

After saving the override, a conf file is created.

$ ll /etc/systemd/system/sumpdata.service.d
total 4
-rw-r--r--. 1 root root 125 Jan 20 10:36 override.conf

$ systemctl daemon-reload
$ systemctl start sumpdata.service
$ systemctl status sumpdata.service
● sumpdata.service - Samp Data service
     Loaded: loaded (/etc/systemd/system/sumpdata.service; disabled; preset: disabled)
    Drop-In: /etc/systemd/system/sumpdata.service.d
             └─override.conf
     Active: active (running) since Sat 2024-01-20 10:21:51 EST; 1s ago
   Main PID: 129986 (java)
      Tasks: 13 (limit: 1061)
     Memory: 69.9M
        CPU: 2.674s
     CGroup: /system.slice/sumpdata.service
             └─129986 /usr/bin/java -jar sumpdata.jar

Make the service start automatically.

$ systemctl enable sumpdata.service
Created symlink /etc/systemd/system/multi-user.target.wants/sumpdata.service → /etc/systemd/system/sumpdata.service.

X. Install Streamlit and clone SumpChart

Clone SumpChart

git clone https://github.com/ntamagawa/sumpchart.git

GitHub Actions for Jar file deployment

NT — Sat, 13 Jan 2024 23:16:01 +0000

This is a memo for a GitHub project that I'm planning to do CI/CD into an AWS instance (likely Lightsail AL2023).

Reference: CI/CD for Java Maven using GitHub Actions

CI/CD Flow

On PR merge to the main branch, run a GitHub action to create a Jar file (aka artifact).
Upload the artifact - meaning make the artifact public
Download the artifact from GitHub

This flow can be done more sophisticated way using a CI/CD tool, but for my purpose, automatically packaging a jar then download using curl is good enough.

GitHub action

Below action set up JDK 21, build the package using Maven, then "upload" the jar file.

name: Package Jar with Maven

on:
  push:
    branches: [ "main" ]
  workflow_dispatch:

jobs:
  build:

    runs-on: ubuntu-latest

    steps:
    - uses: actions/checkout@v3
    - name: Set up JDK 21
      uses: actions/setup-java@v3
      with:
        java-version: '21'
        distribution: 'temurin'
        cache: maven
    - name: Build with Maven
      run: mvn -B package --file pom.xml -DskipTests

    # https://medium.com/@alexander.volminger/ci-cd-for-java-maven-using-github-actions-d009a7cb4b8f
    - name: Upload jar
      run: mkdir staging && cp target/sumpdata-*.jar staging
    - uses: actions/upload-artifact@v4
      with:
        name: Package
        path: staging

Here, the concept of "upload" is a little confusing. What the GitHub action upload-artifact does is to "copy" the jar file to a publicly accessible folder.

Curl Command to Download Jar

Use GitHub REST API, in particular, GitHub Actions Artifact endpoint.

List artifacts

curl https://api.github.com/repos/<Owner>/<Repo>/actions/artifacts

Output

{
  "total_count": 2,
  "artifacts": [
    {
      "id": 1167583720,
      "node_id": "MDg6QXJ0aWZhY3QxMTY3NTgzNzIw",
      "name": "Package",
      "size_in_bytes": 58991355,
      "url": "https://api.github.com/repos/ntamagawa/sumpdata/actions/artifacts/1167583720",
      "archive_download_url": "https://api.github.com/repos/ntamagawa/sumpdata/actions/artifacts/1167583720/zip",
      "expired": false,
      "created_at": "2024-01-13T22:38:33Z",
      "updated_at": "2024-01-13T22:38:33Z",
      "expires_at": "2024-04-12T22:38:10Z",
      "workflow_run": {
        "id": 7515265725,
        "repository_id": 705318802,
        "head_repository_id": 705318802,
        "head_branch": "main",
        "head_sha": "fe3baccee31adbc74b1999c8c3e5c46709bd5ca7"
      }
    },
    {
      "id": 1167559585,
      "node_id": "MDg6QXJ0aWZhY3QxMTY3NTU5NTg1",
      "name": "Package",
      "size_in_bytes": 58991346,
      "url": "https://api.github.com/repos/ntamagawa/sumpdata/actions/artifacts/1167559585",
      "archive_download_url": "https://api.github.com/repos/ntamagawa/sumpdata/actions/artifacts/1167559585/zip",
      "expired": false,
      "created_at": "2024-01-13T21:52:17Z",
      "updated_at": "2024-01-13T21:52:17Z",
      "expires_at": "2024-04-12T21:51:57Z",
      "workflow_run": {
        "id": 7515043712,
        "repository_id": 705318802,
        "head_repository_id": 705318802,
        "head_branch": "main",
        "head_sha": "fe3baccee31adbc74b1999c8c3e5c46709bd5ca7"
      }
    }
  ]
}

Note: It seems that there's no access privilege is required for a public repo.

Download the artifact

I take the archive_download_url from the latest artifact, then download as a zip file.

curl -L -o artifact.zip \
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer <github_token>" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
https://api.github.com/repos/ntamagawa/sumpdata/actions/artifacts/1167559585/zip

Note that you need to generate your own GitHub personal access tokens. See Managing your personal access tokens.
For the above REST API repos/.../actions/artifacts/..., a Read access is required. This page lists what permission is required for REST APIs.

Then, unzip the file which contains the generated jar file.

unzip  artifact.zip

Docker Nginx Memo

NT — Sat, 06 Jan 2024 19:04:04 +0000

Start Nginx on Docker

To run Nginx on Docker:

docker run --name nginx -p 80:80 -d nginx

To restart

docker start -a nginx &

Check if the docker instance working

http://localhost/

Hello World

docker exec -it nginx /bin/bash

Nginx docker image doesn't include vi so I needed to install it (technically, below install vim).

apt update && apt install -y vim

Create index.html

cd /usr/share/nginx/html
vi index2.html

The content of index2.html file might be something like this.


<!DOCTYPE html>
<html>
<head>
  <title>Hello World</title>
</head>
<body>
  <h1>Hello World!</h1>
</body>
</html>

On the browser, access to http://localhost/index2.html.

Reverse Proxy

To use Nginx for the development environment for the Sump Data Project, Nginx is configured as a reverse proxy server.

/etc/nginx/conf.d/default.conf

server {
    listen       80;
    listen  [::]:80;
    server_name  localhost;

    #access_log  /var/log/nginx/host.access.log  main;

    location / {
        root   /usr/share/nginx/html;
        index  index.html index.htm;
    }

    # Swagger is accessed via /swagger url. 
    location /swagger {
    proxy_pass http://host.docker.internal:8080/swagger-ui;
    index index.html;
    proxy_redirect off;
    }

    # This is also for Swagger that requires /v3/... url
    location /v3 {
        proxy_pass http://host.docker.internal:8080/v3;
    proxy_redirect off;
    }

    # This is the sump data endpoint.
    location /devices {
        proxy_pass http://host.docker.internal:8080/devices;
    proxy_redirect off;
    }

    #error_page  404              /404.html;

    # redirect server error pages to the static page /50x.html
    #
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }

}

After editing the conf file, to test

$ nginx -t

To reload the conf file

nginx -s reload

Adding Streamlit

Streamlit is a frontend web application to visualize data. For my project, I'm using it to draw a chart for the sump water level.

I originally just set up the same way as sump data API endpoint. Not that the port 8501 is the Streamlit app port (locally, it can be accessed http://localhost:8501).

    location / {
        proxy_pass http://host.docker.internal:8501/;
        proxy_redirect off;
    }

Unfortunately, this doesn't work. The reason is Streamlit uses WebSocket under _stcore folder. To properly configure the reverse proxy, and HTTP Upgrade needs to be set.

    location /_stcore {
        proxy_pass http://host.docker.internal:8501/_stcore;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_set_header Host $host;
    }

Reference: NGINX as a WebSocket Proxy

My Java Memo

NT — Tue, 31 Oct 2023 01:14:59 +0000

Various findings that would help me later.

java: cannot find symbol error

For example List#getFirst method is a default method of the interface that is implemented since version 21. This doesn't compile well in IntelliJ with default settings.

To make the project allow compiling in Java 21, uncheck the --release option, as the binary won't be compatible with older Java.

Installing Streamlit on Mac

NT — Sat, 28 Oct 2023 13:21:40 +0000

Python

$ brew install python3
$ python3 --version
Python 3.9.6
$ python3 -m pip install --upgrade pip
$ pip3 -V
pip 23.2.1 from /opt/homebrew/lib/python3.11/site-packages/pip (python 3.11)

Venv

$ python3 -m venv venv
$ source venv/bin/activate
(venv) $ pip -V
pip 21.2.4 from /Users/nobu/Playground/st-app/venv/lib/python3.9/site-packages/pip (python 3.9)
(venv) $ python3 -m pip install --upgrade pip
(venv) $ pip -V                              
pip 23.3.1 from /Users/nobu/Playground/st-app/venv/lib/python3.9/site-packages/pip (python 3.9)
(venv) $ deactivate
$  pip -V    
zsh: command not found: pip
$ pip3 -V
pip 23.2.1 from /opt/homebrew/lib/python3.11/site-packages/pip (python 3.11)

Install Streamlit

(venv) $ pip install streamlit

App

app.py

import streamlit as st

st.title('Title of the app')
st.header('The App!')
st.subheader('The future of SumpPump')

Run the app

(venv) $ streamlit run app.py 
  You can now view your Streamlit app in your browser.

  Local URL: http://localhost:8501
  Network URL: http://192.168.1.169:8501

Spring Boot: Multiple Primary Keys via JPA

NT — Wed, 18 Oct 2023 02:38:27 +0000

Goal

I wanted to have a simple database record with 2 primary keys in certain order, with a field that contains a simple value.

Java Persistent API with Spring

Using Java Persistent API (JPA), I thought that this would automatically set up primary keys in the order in the class, but this doesn't work the way intended.

@Entity
public class DataEntry {
    @Id
    private Integer deviceID;
    @Id
    private LocalDateTime measuredOn;

    private Integer value;

/// getters and setters
}

Looking at this web page, I figured I need an ID Class.
https://www.baeldung.com/jpa-composite-primary-keys

public class DataEntryId implements Serializable {
    private Integer deviceID;
    private LocalDateTime measuredOn;

    public DataEntryId(Integer deviceID, LocalDateTime measuredOn) {
        this.deviceID = deviceID;
        this.measuredOn = measuredOn;
    }

/// equals and hashCode
}

With the ID Class defined, now that I can use it as an ID class in the annotation.

@Entity
@IdClass(DataEntryId.class)
public class DataEntry {
///....
}

Running the Spring Boot app with the above would create a table structure correctly when the app started.

mysql> desc data_entry;
+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| deviceid    | int         | NO   | PRI | NULL    |       |
| measured_on | datetime(6) | NO   | PRI | NULL    |       |
| value       | int         | YES  |     | NULL    |       |
+-------------+-------------+------+-----+---------+-------+

mysql> show create table data_entry;
| data_entry | CREATE TABLE `data_entry` (
  `deviceid` int NOT NULL,
  `measured_on` datetime(6) NOT NULL,
  `value` int DEFAULT NULL,
  PRIMARY KEY (`deviceid`,`measured_on`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |

Problem

However, in trying to store a data entry to this table, the following code generate an exception.

        DataEntry dataEntry = new DataEntry();
        dataEntry.setDeviceID(deviceId);
        dataEntry.setMeasuredOn(measuredOn);
        dataEntry.setValue(value);
        dataEntryRepository.save(dataEntry);

Error:
org.hibernate.InstantiationException: Unable to locate constructor for embeddable : com.example.AccessData.DataEntryId

Solution

A subtle requirement in the ID class is that it has to have a default (no arg) constructor.

    public DataEntryId() {
    }

Docker Memo -MySQL

NT — Sun, 15 Oct 2023 20:43:14 +0000

Goal

I just need a MySQL instance for development purpose, but with persisted data.

Storage

There are 2 ways to persist MySQL data, docker volume, or mount a directory on the host machine. For my purpose, I use docker volume.

Create Volume

$ docker volume create sumpdatavolume
$ docker volume ls
(... snip ...)
local     sumpdatavolume

Run MySQL

Run MySQL, create a test db and table.

$ docker run --name sumpdatamysql -d -p 3306:3306 -e MYSQL_ROOT_PASSWORD=myrootpswd -v sumpdatavolume:/var/lib/mysql mysql
$ docker exec -it sumpdatamysql bash
bash-4.4# mysql -pmyrootpswd
mysql> create database test;
use test;
create table test(id int, name varchar(10));
insert into test(id, name) values (1,"John"), (2, "Mike");
select * from test;
+------+------+
| id   | name |
+------+------+
|    1 | John |
|    2 | Mike |
+------+------+

Check persistent data

Remove the existing container and recreate MySQL using the same docker volume.

$ docker stop sumpdatamysql
$ docker rm sumpdatamysql
$ docker run --name sumpdatamysql -d -p 3306:3306 -e MYSQL_ROOT_PASSWORD=myrootpswd -v sumpdatavolume:/var/lib/mysql mysql
$ docker exec -it sumpdatamysql bash
mysql -pmyrootpswd
use test;
select * from test;
+------+------+
| id   | name |
+------+------+
|    1 | John |
|    2 | Mike |
+------+------+

As shown above in select statement, the same data is there.

Run a SpringBoot jar on Docker

NT — Tue, 22 Aug 2023 00:58:18 +0000

Some articles suggest to run a centos docker image to run SpringBoot app. Since CentOS is deprecated, I found that amazoncorretto is an option.

Dockerfile

FROM amazoncorretto:20

VOLUME [ "/data" ]
ADD MySpringBootApp-0.0.1-SNAPSHOT.jar MySpringBootApp
RUN sh -c 'touch /ValidatingFormInput.jar'
ENTRYPOINT [ "java", "-jar", "/MySpringBootApp" ]

Build Docker image

$ docker build -t myspringbootapp .

Note that the Docker image name has to be lower case.

Run the docker container

$ docker run -p 8080:8080 myspringbootapp

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v3.1.1)

2023-08-22T00:41:04.306Z  INFO 1 --- [           main] i.s.s.V.MySpringBootAppApplication   : Starting MySpringBootAppApplication v0.0.1-SNAPSHOT using Java 20.0.2 with PID 1 (/MySpringBootAppApplication.jar started by root in /)
2023-08-22T00:41:04.307Z  INFO 1 --- [           main] i.s.s.V.MySpringBootAppApplication   : No active profile set, falling back to 1 default profile: "default"
2023-08-22T00:41:04.800Z  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2023-08-22T00:41:04.805Z  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2023-08-22T00:41:04.805Z  INFO 1 --- [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.10]
2023-08-22T00:41:04.838Z  INFO 1 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2023-08-22T00:41:04.838Z  INFO 1 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 505 ms
2023-08-22T00:41:05.006Z  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2023-08-22T00:41:05.013Z  INFO 1 --- [           main] i.s.s.V.MySpringBootAppApplication   : Started MySpringBootAppApplication in 0.942 seconds (process running for 1.172)
2023-08-22T00:41:18.153Z  INFO 1 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2023-08-22T00:41:18.153Z  INFO 1 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2023-08-22T00:41:18.154Z  INFO 1 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 1 ms

Set up React on Mac

NT — Tue, 20 Jun 2023 00:40:04 +0000

Install Node.js

Check brew version.

$ brew -v
Homebrew 4.0.23

Install nodebrew

Following this post, I decided to install nodebrew. I won't be an active frontend developer, but this might help in the future to switch or maintain versions of npm as described.
https://fromscratch-y.work/en/blog/programming/mac-nodejs-install/#sec4-1

$ brew install nodebrew
(...snip...)
==> Caveats
You need to manually run setup_dirs to create directories required by nodebrew:
  /opt/homebrew/opt/nodebrew/bin/nodebrew setup_dirs

Add path:
  export PATH=$HOME/.nodebrew/current/bin:$PATH

To use Homebrew's directories rather than ~/.nodebrew add to your profile:
  export NODEBREW_ROOT=/opt/homebrew/var/nodebrew

zsh completions have been installed to:
  /opt/homebrew/share/zsh/site-functions
==> Summary
🍺  /opt/homebrew/Cellar/nodebrew/1.2.0: 8 files, 40.6KB

(...snip...)

Not sure what the setup_dirs does...

Added the PATH to my .zshrc

$ echo 'export PATH=$HOME/.nodebrew/current/bin:$PATH' >> ~/.zshrc 
$ source ~/.zshrc

Specify the node version

$ nodebrew ls-remote
v0.0.1    v0.0.2    v0.0.3    v0.0.4    v0.0.5    v0.0.6    

v0.1.0    v0.1.1    v0.1.2    v0.1.3    v0.1.4    v0.1.5    v0.1.6    v0.1.7
(...snip...)

v20.0.0   v20.1.0   v20.2.0   v20.3.0   
(...snip...)

io@v3.0.0 io@v3.1.0 io@v3.2.0 io@v3.3.0 io@v3.3.1

Install the stable version

$ nodebrew install stable
$ nodebrew list
v20.3.0

Activate the installed version

$ nodebrew use v20.3.0
use v20.3.0
$ node -v
v20.3.0
$ npm -v
9.6.7

Create an app

$ npx create-react-app react-app

According to this page https://react.dev/learn/start-a-new-react-project, that creates Next.js project.

To run, go down to the created project folder, and start npm.

$ cd react-app
$ npm start

This automatically opens http://localhost:3000 with your default browser and show the starter page.

Further more, below comment will create a build folder for deployment.

$  npm run build

Source: https://create-react-app.dev/docs/deployment/

My plan it to run a server using Spring Boot.

Why React?

As a Java backend developer, I need to work with frontend developers. Also wanted to set up a simple website based on Java backend, and picked React as the FE framework - simply because it's most trending framework on the FE side.

Setting up IntelliJ Community Edition

NT — Sat, 17 Jun 2023 22:27:32 +0000

Install JDK

$ brew install openjdk
$ sudo ln -sfn /opt/homebrew/opt/openjdk/libexec/openjdk.jdk /Library/Java/JavaVirtualMachines/openjdk.jdk
echo 'export PATH="/opt/homebrew/opt/openjdk/bin:$PATH"' >> ~/.zshrc
$ echo 'export CPPFLAGS="-I/opt/homebrew/opt/openjdk/include"' >> ~/.zshrc
$ source ~/.zshrc
$ java --version
openjdk 20.0.1 2023-04-18
OpenJDK Runtime Environment Homebrew (build 20.0.1)
OpenJDK 64-Bit Server VM Homebrew (build 20.0.1, mixed mode, sharing)

Install IntelliJ Community Edition

https://www.jetbrains.com/idea/download/?var=1&section=mac

Spring Boot Project

Use initializer to create a new project

https://start.spring.io

Select Maven
Add Spring Web dependency
Select the correct Java version

Open the project in IntelliJ CE

Trust the project
Specify JDK in Project Structure
Add a controller

package com.example.demo;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloWorldController {
    @RequestMapping("/")
    public String hello()
    {
        return "Hello Spring Boot!";
    }
}

Build project
Run the project

Open a browser and point to localhost:8080 to verify the web application is running