Pass URL from K8s-ConfigMap to SpringBoot Application - spring-boot

Question

I'm quite new to Kubernetes and started using MiniKube to experiment with K8s.
Explanation
This is the (very simple) scenario I want to realize:
PrintClient provides a http-endpoint: <url>/<stringToPrint>
PrintClient redirects <stringToPrint> to PrintServer
PrintServer just print out <stringToPrint> in console
The scenario is meant as a proof-of-concept, and will be the basis for a evaluation in the company I'm working at, therefore it needs to accomplish the following tasks:
both applications are running inside the MiniKube-cluster
PrintClient should have an ExternalService
PrintServer should have an InternalService
the URL for PrintServer should come from a ConfigMap using
PrintServer's InternalService
Code
Here are the relevant files for my scenario.
At first I show you the code of both applications:
PrintClient
PrintClientApplication.java
#SpringBootApplication
public class PrintClientApplication {
public static void main(String[] args) {
SpringApplication.run(PrintClientApplication.class, args);
}
#Bean
public RestTemplate getRestTemplate(RestTemplateBuilder builder) {
return builder.build();
}
}
Api.java
#RestController
public class Api {
#Autowired
private RestTemplate rs;
#Value("${PRINT_SERVER_URL}")
private String printServerUrl;
#GetMapping("/{string}")
public void print(#PathVariable("string")String string) {
System.out.println(printServerUrl);
rs.getForObject( printServerUrl + string, String.class);
}
}
application.properties
PRINT_SERVER_URL=thisIsJustAPlaceholder
Dockerfile
FROM java:8-jdk-alpine
COPY /target/print_client-0.0.1-SNAPSHOT.jar /usr/app/
ENV PRINT_SERVER_URL=blah
WORKDIR /usr/app/
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "print_client-0.0.1-SNAPSHOT.jar", "PRINT_SERVER_URL=${PRINT_SERVER_URL}"]
deployment+service
apiVersion: apps/v1
kind: Deployment
metadata:
name: print-client-deployment
spec:
selector:
matchLabels:
app: print-client-label
replicas: 1
template:
metadata:
labels:
app: print-client-label
spec:
containers:
- name: print-client
image: patrickshaikh/print_client:1
ports:
- containerPort: 8080
env:
- name: PRINT_SERVER_URL
valueFrom:
configMapKeyRef:
name: print-client-configmap
key: print_server_url
---
apiVersion: v1
kind: Service
metadata:
name: print-client-service
spec:
selector:
app: print-client-label
type: LoadBalancer
ports:
- protocol: TCP
port: 8080
targetPort: 8080
nodePort: 30001
configmap
apiVersion: v1
kind: ConfigMap
metadata:
name: print-client-configmap
data:
print_server_url: print-server-service
PrintServer
Api.java
#RestController
public class Api {
#GetMapping("/{string}")
public void hello(#PathVariable("string") String string) {
System.out.println(string);
}
}
deployment+service
apiVersion: apps/v1
kind: Deployment
metadata:
name: print-server-deployment
spec:
selector:
matchLabels:
app: print-server
replicas: 1
template:
metadata:
labels:
app: print-server
spec:
containers:
- name: print-server
image: patrickshaikh/print_server:1
ports:
- containerPort: 8080
---
apiVersion: v1
kind: Service
metadata:
name: print-server-service
spec:
selector:
app: print-server
type: LoadBalancer
ports:
- protocol: TCP
port: 8080
targetPort: 8080
nodePort: 30000
(It is an ExternalService for testing purpose, but will be internal later.)
I already checked if CoreDNS is running:
Misbehaviour
I used the name of the print-server-service in the ConfigMap but instead of resolving it to an URL before passing the value to the container on initialization, it treats it as a string (during a testiteration I printed the URL to console as well).
Using the IP of PrintServers InternalService results in a 404 while using the IP of its ExternalService works flawlessly.
Questions at answerers
Why can't it resolve the reference to the print-server-service to
its internal IP?
What would be the proper way of passing URLs to a container using
servicenames?
Is there anything else in terms of "best practice" in my scenario i
could adapt?
Thanks in advance