From e5334c7d57cc8a5e28f8cf4b7b2d15685b7a0194 Mon Sep 17 00:00:00 2001
From: EddeCCC <eduard.schander@gmx.de>
Date: Mon, 13 May 2024 15:48:39 +0200
Subject: [PATCH] add method to inject eum-host dynamically from ENV variable

---
 .../petclinic/api/ApiGatewayApplication.java  | 24 ++++++++++++++++++-
 .../src/main/resources/static/index.html      | 16 +++++++------
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/ApiGatewayApplication.java b/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/ApiGatewayApplication.java
index df86a6fc2..b5716ee35 100644
--- a/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/ApiGatewayApplication.java
+++ b/spring-petclinic-api-gateway/src/main/java/org/springframework/samples/petclinic/api/ApiGatewayApplication.java
@@ -36,6 +36,8 @@
 import org.springframework.web.reactive.function.server.RouterFunctions;
 import org.springframework.web.reactive.function.server.ServerResponse;
 
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 
 
@@ -65,6 +67,9 @@ public WebClient.Builder loadBalancedWebClientBuilder() {
     @Value("classpath:/static/index.html")
     private Resource indexHtml;
 
+    @Value("${EUM_HOST:localhost}")
+    private String eumHost;
+
     /**
      * workaround solution for forwarding to index.html
      * @see <a href="https://github.com/spring-projects/spring-boot/issues/9785">#9785</a>
@@ -73,10 +78,27 @@ public WebClient.Builder loadBalancedWebClientBuilder() {
     RouterFunction<?> routerFunction() {
         RouterFunction router = RouterFunctions.resources("/**", new ClassPathResource("static/"))
             .andRoute(RequestPredicates.GET("/"),
-                request -> ServerResponse.ok().contentType(MediaType.TEXT_HTML).bodyValue(indexHtml));
+                request -> ServerResponse.ok().contentType(MediaType.TEXT_HTML)
+                    .bodyValue(injectDynamicEumHost())
+            );
         return router;
     }
 
+    /**
+     * workaround solution to use dynamic hosts for EUM instead of just localhost
+     * @return content of index.html with injected EUM-Host
+     */
+    private String injectDynamicEumHost() {
+        try {
+            String indexHtmlContent = new String(indexHtml.getInputStream().readAllBytes(), StandardCharsets.UTF_8);
+
+            // Replace the placeholder with the actual host value
+            return indexHtmlContent.replace("${EUM_HOST}", eumHost);
+        } catch (IOException e) {
+            throw new RuntimeException("Could not read index.html");
+        }
+    }
+
     /**
      * Default Resilience4j circuit breaker configuration
      */
diff --git a/spring-petclinic-api-gateway/src/main/resources/static/index.html b/spring-petclinic-api-gateway/src/main/resources/static/index.html
index 1cc2a872d..5fd8ee65e 100644
--- a/spring-petclinic-api-gateway/src/main/resources/static/index.html
+++ b/spring-petclinic-api-gateway/src/main/resources/static/index.html
@@ -50,15 +50,17 @@
     <script src="/scripts/infrastructure/infrastructure.js"></script>
     <script src="/scripts/infrastructure/httpErrorHandlingInterceptor.js"></script>
 
-    <script src="http://localhost:8085/boomerang/boomerang.js"></script>
-    <script src="http://localhost:8085/boomerang/plugins/boomerang-opentelemetry.js"></script>
-    <script src="http://localhost:8085/boomerang/plugins/rt.js"></script>
-    <script src="http://localhost:8085/boomerang/plugins/auto-xhr.js"></script>
-    <script src="http://localhost:8085/boomerang/plugins/spa.js"></script>
-    <script src="http://localhost:8085/boomerang/plugins/history.js"></script>
+    <!-- ${EUM_HOST} will be replaced with an actual host, while loading the file -->
+    <!-- see ApiGatewayApplication#injectDynamicEumHost() -->
+    <script src="http://${EUM_HOST}:8085/boomerang/boomerang.js"></script>
+    <script src="http://${EUM_HOST}:8085/boomerang/plugins/boomerang-opentelemetry.js"></script>
+    <script src="http://${EUM_HOST}:8085/boomerang/plugins/rt.js"></script>
+    <script src="http://${EUM_HOST}:8085/boomerang/plugins/auto-xhr.js"></script>
+    <script src="http://${EUM_HOST}:8085/boomerang/plugins/spa.js"></script>
+    <script src="http://${EUM_HOST}:8085/boomerang/plugins/history.js"></script>
     <script>
         BOOMR.init({
-            beacon_url: "http://localhost:8085/beacon/"
+            beacon_url: "http://${EUM_HOST}:8085/beacon/"
         });
     </script>