For several days I've had a configuration problem with Nginx that I can't solve.
I'm a beginner, and I'd just like to **run my Spring Boot application on the main domain name**, and run simple applications (to test, initially simple HTML pages) on **sub-domains (of the same domain name)**.
Preliminary remark:


I've built my API with Spring Boot, which uses a TomCat web server. Spring Boot APIs run on port 8080 by default.
A Spring Boot application can therefore run without Nginx
So I don't have any configuration for my API, which is accessible via the main domain name (which does point to the VPS server's IP address), which is:
http://musicstoreapi.com:8080/api/products.
What I want to do:

Run my Spring Boot API only on the main domain name, i.e. musicstoreapi.com, on port 8080. It works.
When calling the sub-domains api1.musicstoreapi.com, api2.musicstoreapi.com, api3.musicstoreapi.com, these sub-domains must return a simple HTML page.
I therefore set up an Nginx configuration for these sub-domains so that the web server displays the correct HTML page (which is in /var/www/api1 for the sub-domain api1.musicstoreapi.com, in /var/www/api2 for the sub-domain api2.musicstoreapi.com, and in /var/www/api3 for the sub-domain api3.musicstoreapi.com.)
What's happening now ? What's the problem ?

- When I call http://musicstoreapi.com:8080/api/products I get the data from my Spring Boot API correctly. - However, I don't understand why I'm getting my Spring Boot API data for:
http://api1.musicstoreapi.com:8080/api/products or
http://api2.musicstoreapi.com:8080/api/products or
http://api3.musicstoreapi.com:8080/api/products.
I'm supposed to **get API datas ONLY for the main domain name not for the sub-domains !**
So **normally I should expect to get a 404** for :
http://api1.musicstoreapi.com:8080/api/products or
http://api2.musicstoreapi.com:8080/api/products or
http://api3.musicstoreapi.com:8080/api/products. - As for the sub-domains, http://api1.musicstoreapi.com, and http://api2.musicstoreapi.com, the **server should display their respective HTML pages**.
I'll try to be as precise as possible so that you can help me solve my configuration problem.
Diagram of my configuration problem:

In case I've expressed myself badly, I thought I'd draw a diagram so that you can clearly understand the problem, i.e. what I'm getting versus what I'm supposed to be getting:

Configuration & files

1. DNS
Here's a screenshot of the DNS configuration for my domain name:
Name : musicstoreapi.com
Type : A
Value : IP VPS
Name : www. musicstoreapi.com
Type : A
Value : IP VPS
Name : api1. musicstoreapi.com
Type : CNAME
Value: musicstoreapi.com
Name : api2. musicstoreapi.com
Type : CNAME
Value: musicstoreapi.com
Name : api3. musicstoreapi.com
Type : CNAME
Value: musicstoreapi.com


2. Jar file (for my Spring Boot Application)

-----@-------: /etc/nginx/sites-enabled# cd /home/applications
-----@-------: /home/applications# ls
spring-boot-ecommerce-0.0.1-SNAPSHOT.jar
Precision:The name of the .jar file appears in red, but it seems to run correctly.

3. Service


To ensure that my Spring Boot application is accessible without interruption, I've created a service that appears to be active:
spring-boot-ecommerce.service - Spring Boot Ecommerce Application
Loaded: loaded (/etc/systemd/system/spring-boot-ecommerce.service; enabled; vendor preset: enabled)
Active: active (running) since Fri 2024-02-09 14:13:52 UTC; 2min 16s ago
Main PID: 476505 (java)
Tasks: 40 (limit: 19140)
Memory: 330.0M
CPU: 19.428s
CGroup: /system.slice/spring-boot-ecommerce.service
└─476505 /usr/bin/java -jar /home/applications/spring-boot-ecommerce-0.0.1-SNAPSHOT.jar

Feb 09 14:13:55 --------- java[476505]: 2024-02-09T14:13:55.389Z INFO 476505 --- [ main] org.hibernate.Version : HHH000412: Hibernate ORM core version 6.2.13.Final
Feb 09 14:13:55 --------- java[476505]: 2024-02-09T14:13:55.392Z INFO 476505 --- [ main] org.hibernate.cfg.Environment : HHH000406: Using bytecode reflection optimizer
Feb 09 14:13:55 --------- java[476505]: 2024-02-09T14:13:55.756Z INFO 476505 --- [ main] o.s.o.j.p.SpringPersistenceUnitInfo : No LoadTimeWeaver setup: ignoring JPA class transformer
Feb 09 14:13:55 --------- java[476505]: 2024-02-09T14:13:55.825Z WARN 476505 --- [ main] org.hibernate.orm.deprecation : HHH90000025: MySQL8Dialect does not need to be specified explicitly >
Feb 09 14:13:55 --------- java[476505]: 2024-02-09T14:13:55.826Z WARN 476505 --- [ main] org.hibernate.orm.deprecation : HHH90000026: MySQL8Dialect has been deprecated; use org.hibernate.di>
Feb 09 14:13:56 --------- java[476505]: 2024-02-09T14:13:56.866Z INFO 476505 --- [ main] o.h.e.t.j.p.i.JtaPlatformInitiator : HHH000489: No JTA platform available (set 'hibernate.transaction.jta>
Feb 09 14:13:56 --------- java[476505]: 2024-02-09T14:13:56.869Z INFO 476505 --- [ main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
Feb 09 14:13:57 --------- java[476505]: 2024-02-09T14:13:57.316Z WARN 476505 --- [ main] JpaBaseConfiguration$JpaWebConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database q>
Feb 09 14:13:58 --------- java[476505]: 2024-02-09T14:13:58.406Z INFO 476505 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
Feb 09 14:13:58 --------- java[476505]: 2024-02-09T14:13:58.426Z INFO 476505 --- [ main] c.l.e.SpringBootEcommerceApplication : Started SpringBootEcommerceApplication in 5.779 seconds (process run>


4. UFW Status

To Action From
-- ------ ----
22/tcp ALLOW Anywhere
80/tcp ALLOW Anywhere
443 ALLOW Anywhere
8433:8443/tcp ALLOW Anywhere
3306 ALLOW Anywhere
8080 ALLOW Anywhere
88 ALLOW Anywhere
81 ALLOW Anywhere
22/tcp (v6) ALLOW Anywhere (v6)
80/tcp (v6) ALLOW Anywhere (v6)
443 (v6) ALLOW Anywhere (v6)
8433:8443/tcp (v6) ALLOW Anywhere (v6)
3306 (v6) ALLOW Anywhere (v6)
8080 (v6) ALLOW Anywhere (v6)
88 (v6) ALLOW Anywhere (v6)
81 (v6) ALLOW Anywhere (v6)



5. Nginx Configuration File
server {
listen 80;
listen [::]:80;
server_name api1.musicstoreapi.com;
root /var/www/api1;
index index.html;

location / {
try_files $uri $uri/ =404;
}
}

server {
listen 80;
listen [::]:80;
server_name www.api1.musicstoreapi.com;
root /var/www/api1;
index index.html;

location / {
try_files $uri $uri/ =404;
}
}

server {
listen 80;
listen [::]:80;
server_name www.api2.musicstoreapi.com;
root /var/www/api2;
index index.html;

location / {
try_files $uri $uri/ =404;
}
}
server {
listen 80;
listen [::]:80;
server_name api2.musicstoreapi.com;
root /var/www/api2;
index index.html;


location / {
try_files $uri $uri/ =404;
}
}


6. Symbolic link
In the /etc/nginx/sites-enabled folder, the symbolic link to the configuration file (which is in /etc/nginx/sites-available/musicstoreapi.com) has been made:
-----@-------:/etc/nginx/sites-enabled# cd /etc/nginx/sites-enabled
-----@-------:/etc/nginx/sites-enabled# ls -alh
total 12K
drwxr-xr-x 2 root root 4.0K Jan 27 16:30 .
drwx------ 12 root root 4.0K Feb 9 14:28 ..
-rw-r--r-- 1 root root 192 Nov 17 2022 default.conf
lrwxrwxrwx 1 root root 44 Jan 27 16:30 musicstoreapi.com -> /etc/nginx/sites-available/musicstoreapi.com


7. Directory and file permissions
(Same for api2 and api3)
-----@-------:/var/www/api1# ls -ld /var/www/api1
drwxrwxr-x 2 root root 4096 Feb 9 15:19 /var/www/api1

I hope all these clarifications will help me find the problem. I've been using chatGPT but it's going round in circles and I've already done everything it suggested.