From 5fc1065d8cb81fcd68a9ab95d6b0b5846bb25aaf Mon Sep 17 00:00:00 2001
From: Adrian Cole <adrian@tetrate.io>
Date: Wed, 21 Feb 2024 11:36:22 +0800
Subject: [PATCH] Allows overriding the BACKEND_ENDPOINT via env

When deployed in the same k8s pod, services communicate by localhost
despite being in different docker containers. By adding
`BACKEND_ENDPOINT`, we can set this to "http://localhost:9000/api" in
a k8s "extra container', so that we can do "helm test" on it.

See https://kubernetes.io/docs/concepts/workloads/pods/#pod-networking

Signed-off-by: Adrian Cole <adrian@tetrate.io>
---
 .../src/main/java/brave/example/Frontend.java |  9 +++++++-
 docker/bin/install-example                    | 21 ++++++++++++-------
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/armeria/src/main/java/brave/example/Frontend.java b/armeria/src/main/java/brave/example/Frontend.java
index d8dc57d..d3dd98d 100644
--- a/armeria/src/main/java/brave/example/Frontend.java
+++ b/armeria/src/main/java/brave/example/Frontend.java
@@ -8,14 +8,21 @@
 import com.linecorp.armeria.server.healthcheck.HealthCheckService;
 import com.linecorp.armeria.server.logging.AccessLogWriter;
 import com.linecorp.armeria.server.logging.LoggingService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public final class Frontend {
+  static final Logger LOGGER = LoggerFactory.getLogger(HttpTracingFactory.class);
 
   public static void main(String[] args) {
     final HttpTracing httpTracing = HttpTracingFactory.create("frontend");
 
+    final String backendEndpoint =
+        System.getProperty("backend.endpoint", "http://127.0.0.1:9000/api");
+    LOGGER.info("Using backend endpoint: {}", backendEndpoint);
+
     final WebClient backendClient =
-        WebClient.builder(System.getProperty("backend.endpoint", "http://127.0.0.1:9000/api"))
+        WebClient.builder(backendEndpoint)
             .decorator(BraveClient.newDecorator(httpTracing.clientOf("backend")))
             .build();
 
diff --git a/docker/bin/install-example b/docker/bin/install-example
index 79d6545..2167a53 100755
--- a/docker/bin/install-example
+++ b/docker/bin/install-example
@@ -28,19 +28,23 @@ tee -a start-frontend start-backend <<-'EOF'
 export IP="$(hostname -i || echo '127.0.0.1')"
 EOF
 
+# Declare variables that expand variables set in this shell script/
+# These don't need to be exported as they are converted to java properties.
 cat >> start-frontend <<-EOF
-export PORT=${frontend_port}
-export EXAMPLE=${version}
-export EXAMPLE_SERVICE=frontend
+PORT=${frontend_port}
+EXAMPLE=${version}
+EXAMPLE_SERVICE=frontend
+DEFAULT_BACKEND_ENDPOINT=http://backend:${backend_port}/api
 EOF
 
 cat >> start-backend <<-EOF
-export PORT=${backend_port}
-export EXAMPLE=${version}
-export EXAMPLE_SERVICE=backend
+PORT=${backend_port}
+EXAMPLE=${version}
+EXAMPLE_SERVICE=backend
 EOF
 
-# Add common elements for Java applications
+# Add common elements for Java applications.
+# HEALTHCHECK variables need to be exported as they are read via proc info.
 tee -a start-frontend start-backend <<-'EOF'
 export HEALTHCHECK_IP=${IP}
 export HEALTHCHECK_PORT=${PORT}
@@ -55,7 +59,8 @@ exec java ${JAVA_OPTS} -cp 'classes:lib/*' \
 -Dzipkin.baseUrl=${ZIPKIN_BASEURL:-http://zipkin:9411/} \
 EOF
 
-echo "-Dbackend.endpoint=http://backend:${backend_port}/api \\" >> start-frontend
+# Allow override of the backend endpoint, for a multi-container pod.
+echo '-Dbackend.endpoint=${BACKEND_ENDPOINT:-${DEFAULT_BACKEND_ENDPOINT}} \' >> start-frontend
 
 # Add the main class
 echo 'brave.example.Frontend "$@"' >> start-frontend