Added optional NODE env var

Signed-off-by: Philip Schmid <[email protected]>

README.md

@@ -2,10 +2,11 @@
 
 ![Build and Push Docker Image](https://github.com/philipschmid/echo-app/actions/workflows/build.yaml/badge.svg) ![Go Syntax and Format Check](https://github.com/philipschmid/echo-app/actions/workflows/test.yaml/badge.svg)
 
-Tiny golang app which returns a timestamp, a customizable message, the hostname, the request source IP, and optionally the HTTP request headers.
+Tiny golang app which returns a timestamp, a customizable message, the hostname, the request source IP, the node name (if set), and optionally the HTTP request headers.
 
 ## Configuration Options
 - `MESSAGE`: A customizable message to be returned in the JSON response. If not set, no message will be displayed.
+- `NODE`: The name of the node where the app is running. This is typically used in a Kubernetes environment.
 - `PORT`: The port number on which the server listens. Default is `8080`.
 - `PRINT_HTTP_REQUEST_HEADERS`: Set to `true` to include HTTP request headers in the JSON response. By default, headers are not included.
 
@@ -15,6 +16,8 @@ Shell 1 (server):
 docker run -it -p 8080:8080 ghcr.io/philipschmid/echo-app:main
 # Optionally with a customized message:
 docker run -it -p 8080:8080 -e MESSAGE="demo-env" ghcr.io/philipschmid/echo-app:main
+# Optionally with a node name:
+docker run -it -p 8080:8080 -e NODE="k8s-node-1" ghcr.io/philipschmid/echo-app:main
 # Optionally include HTTP request headers in the response:
 docker run -it -p 8080:8080 -e PRINT_HTTP_REQUEST_HEADERS="true" ghcr.io/philipschmid/echo-app:main
 ```
@@ -27,16 +30,16 @@ curl http://localhost:8080/
 You should see a similar client output like this:
 ```json
 {"timestamp":"2024-05-28T19:50:10.289Z","hostname":"83ff0b127ed6","source_ip":"192.168.65.1"}
-{"timestamp":"2024-05-28T19:50:35.022Z","message":"Hello World!","hostname":"4495529ebd32","source_ip":"192.168.65.1"}
+{"timestamp":"2024-05-28T19:50:35.022Z","message":"Hello World!","hostname":"4495529ebd32","source_ip":"192.168.65.1","node":"k8s-node-1"}
 ```
 
 If `PRINT_HTTP_REQUEST_HEADERS` is set to `true`, the response will also include the request headers:
 ```json
-{"timestamp":"2024-05-28T20:21:23.363Z","hostname":"3f96391b04f2","source_ip":"192.168.65.1","headers":{"Accept":["*/*"],"User-Agent":["curl/8.6.0"]}}
+{"timestamp":"2024-05-28T20:21:23.363Z","hostname":"3f96391b04f2","source_ip":"192.168.65.1","node":"k8s-node-1","headers":{"Accept":["*/*"],"User-Agent":["curl/8.6.0"]}}
 ```
 
 ## Kubernetes
-Apply the following manifests:
+Apply the following manifests to deploy the echo-app with the `NODE` environment variable set to the name of the Kubernetes node using the Downward API:
 ```yaml
 ---
 apiVersion: v1
@@ -91,6 +94,11 @@ spec:
             configMapKeyRef:
               name: echo-app-config
               key: PRINT_HTTP_REQUEST_HEADERS
+        # Add the NODE environment variable using the downward API
+        - name: NODE
+          valueFrom:
+            fieldRef:
+              fieldPath: spec.nodeName
 ---
 apiVersion: v1
 kind: Service
@@ -111,5 +119,16 @@ Shell 2 (client):
 kubectl run netshoot --rm -it --image=nicolaka/netshoot -- curl http://echo-app-service:8080
 ```
 
+You should see a similar client output like this:
+```json
+{"timestamp":"2024-05-28T19:50:35.022Z","message":"demo-env","hostname":"echo-app-deployment-5d8f8b8b8b-9t4kq","source_ip":"10.1.0.1","node":"k8s-node-1"}
+```
+
+If `PRINT_HTTP_REQUEST_HEADERS` is set to `true`, the response will also include the request headers:
+```json
+{"timestamp":"2024-05-28T20:21:23.363Z","message":"demo-env","hostname":"echo-app-deployment-5d8f8b8b8b-9t4kq","source_ip":"10.1.0.1","node":"k8s-node-1","headers":{"Accept":["*/*"],"User-Agent":["curl/8.6.0"]}}
+```
+
 ## Credit
-Basic idea (& source code) is taken from https://cloud.google.com/kubernetes-engine/docs/samples/container-hello-app.
+Basic idea (& source code) is taken from https://cloud.google.com/kubernetes-engine/docs/samples/container-hello-app.
+```

main.go

@@ -14,14 +14,16 @@ import (
 type Response struct {
 	Timestamp string              `json:"timestamp"`
 	Message   *string             `json:"message,omitempty"`
-	Hostname  string              `json:"hostname"`
 	SourceIP  string              `json:"source_ip"`
+	Hostname  string              `json:"hostname"`
+	Node      *string             `json:"node,omitempty"`    // Optional field to include node name
 	Headers   map[string][]string `json:"headers,omitempty"` // Optional field to include headers
 }
 
 func main() {
 	// Get MESSAGE and PRINT_HTTP_REQUEST_HEADERS environment variables
 	messagePtr := getMessagePtr()
+	nodePtr := getNodePtr()
 	printHeaders := getPrintHeadersSetting()
 
 	// Prepare the message log
@@ -30,9 +32,25 @@ func main() {
 		messageLog = "MESSAGE environment variable set to: " + *messagePtr
 	}
 
+	// Prepare the node log
+	nodeLog := "No NODE environment variable set"
+	if nodePtr != nil {
+		nodeLog = "NODE environment variable set to: " + *nodePtr
+	}
+
+	// Print optional configs on multiple lines
+	log.Println("Server configuration:")
+	log.Printf("  %s\n", messageLog)
+	log.Printf("  %s\n", nodeLog)
+	if printHeaders {
+		log.Println("  PRINT_HTTP_REQUEST_HEADERS is enabled")
+	} else {
+		log.Println("  PRINT_HTTP_REQUEST_HEADERS is disabled")
+	}
+
 	// Register hello function to handle all requests
 	mux := http.NewServeMux()
-	mux.HandleFunc("/", hello(messagePtr, printHeaders)) // Pass message pointer and printHeaders to the hello function
+	mux.HandleFunc("/", hello(messagePtr, nodePtr, printHeaders)) // Pass message and node pointers and printHeaders to the hello function
 
 	// Use PORT environment variable, or default to 8080
 	port := os.Getenv("PORT")
@@ -41,12 +59,12 @@ func main() {
 	}
 
 	// Start the web server on port and accept requests
-	log.Printf("Server listening on port %s (%s)", port, messageLog)
+	log.Printf("Server listening on port %s\n", port)
 	log.Fatal(http.ListenAndServe(":"+port, mux))
 }
 
 // hello returns a http.HandlerFunc that uses the provided message pointer and printHeaders flag.
-func hello(messagePtr *string, printHeaders bool) http.HandlerFunc {
+func hello(messagePtr *string, nodePtr *string, printHeaders bool) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		// Get the IP address without the port number
 		ip, _, err := net.SplitHostPort(r.RemoteAddr)
@@ -68,6 +86,7 @@ func hello(messagePtr *string, printHeaders bool) http.HandlerFunc {
 			Timestamp: timestamp,
 			Message:   messagePtr,
 			Hostname:  host,
+			Node:      nodePtr,
 			SourceIP:  ip,
 		}
 
@@ -100,6 +119,15 @@ func getMessagePtr() *string {
 	return &message
 }
 
+// getNodePtr gets the NODE environment variable and returns a pointer to it, or nil if it's not set.
+func getNodePtr() *string {
+	node := os.Getenv("NODE")
+	if node == "" {
+		return nil
+	}
+	return &node
+}
+
 // getPrintHeadersSetting checks the PRINT_HTTP_REQUEST_HEADERS environment variable.
 func getPrintHeadersSetting() bool {
 	return strings.ToLower(os.Getenv("PRINT_HTTP_REQUEST_HEADERS")) == "true"