Ingress creates location / (root path match all) in nginx config on specific servername, avoiding path to be found on default servername - kubernetes-ingress

Question

I am running into this problem (or behave) of Ingress I can't understand:
If I have a path: /api1 configed in ingess without a specified host name, like this:
apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
name: api1
namespace: somenamespace
annotations:
kubernetes.io/ingress.class: "nginx"
nginx.ingress.kubernetes.io/proxy-body-size: 100m
nginx.ingress.kubernetes.io/proxy-read-timeout: "300"
nginx.ingress.kubernetes.io/proxy-send-timeout: "300"
nginx.ingress.kubernetes.io/proxy-connect-timeout: "300"
spec:
rules:
- http:
paths:
- path: /api1
pathType: ImplementationSpecific
backend:
serviceName: service-for-api1
servicePort: 1234
Then I can access this path in any hostname or IP address as long as it points to my server, e.g. my-server.com/api1 or 1.2.3.4/api1
And If I added another ingress config with a specified host name, like: /api2
apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
name: api2
namespace: somenamespace
annotations:
kubernetes.io/ingress.class: "nginx"
nginx.ingress.kubernetes.io/proxy-body-size: 100m
nginx.ingress.kubernetes.io/proxy-read-timeout: "300"
nginx.ingress.kubernetes.io/proxy-send-timeout: "300"
nginx.ingress.kubernetes.io/proxy-connect-timeout: "300"
spec:
rules:
- host: my-server.com # Only difference is this one has a host field
http:
paths:
- path: /api2
pathType: ImplementationSpecific
backend:
serviceName: service-for-api2
servicePort: 1234
Then I can access my-server.com/api2 all right, But when accessing my-server.com/api1, I got a 404 not found error. If try to access through IP, 1.2.3.4/api1, It works all right.
I read the nginx config generated by ingress, found out when no host is specified in ingress config, the path rule (/api1) will be added to servername _ which is the default server of nginx. And once a hostname is provided in ingress config, It (/api2) will be added to servername hostname block in nginx configfile. Also there will be a location / rule to match all path in this hostname, preventing all paths fallback to default server. So when access my-server.com/api2, the route is okey but when access my-server.com/api1, It matches location / in servername my-server.com block, preventing default server functioning at all.
Why do ingress do this??
I was believing not specify any hostname in ingress config means host: *, thus any host can match the rule. But it behaves like only hostname unknown to ingress can match host: *.
The nginx config I looked at is like this (forgive my for only copying part of it):
## start server _
server {
server_name _ ;
listen 80 default_server reuseport backlog=65535 ;
listen [::]:80 default_server reuseport backlog=65535 ;
listen 443 default_server reuseport backlog=65535 ssl http2 ;
listen [::]:443 default_server reuseport backlog=65535 ssl http2 ;
set $proxy_upstream_name "-";
...
location /api1 {
...
}
...
}
## end server _
## start server my-server.com
server {
server_name my-server.com
listen 80 ;
listen [::]:80 ;
listen 443 ssl http2 ;
listen [::]:443 ssl http2 ;
set $proxy_upstream_name "-";
location /api2 {
....
}
location / {
set $namespace "somenamespace";
set $ingress_name "service-for-api2";
set $service_name "";
set $service_port "";
set $location_path "/";
set $global_rate_limit_exceeding n;
...
# In case of errors try the next upstream server before returning an error
proxy_next_upstream error timeout;
proxy_next_upstream_timeout 0;
proxy_next_upstream_tries 3;
...
}
}
## end server my-server.com
When copying I noticed the "try the next upstream server before returning an error", Is it not work properly so I got a 404 instead of actually trying servername _ ? When I looked the nginx log, it said the 404 request is sent to service [upstream-default-backend], I don't know what it means.
After I discover this problem I deleted the specified hostname in /api2 and it work allright. But I jsut can't help wondering why ingress does this behave...