fix: configure Kafka brokers at runtime

docker/tinode/config.template

@@ -128,7 +128,7 @@
 
 	"kafka": {
 		"enabled": true,
-		"brokers": ["kafka.118im.com:30835"],
+		"brokers": $KAFKA_BROKERS_JSON,
 		"client_id": "im-server",
 		"consumer_group": "im-server",
 		"dial_timeout_ms": 3000,

server/docker_config_template_test.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestDockerConfigUsesKafkaBrokersFromEnvironment(t *testing.T) {
+	content, err := os.ReadFile("../docker/tinode/config.template")
+	if err != nil {
+		t.Fatalf("read Docker config template: %v", err)
+	}
+
+	template := string(content)
+	if !strings.Contains(template, `"brokers": $KAFKA_BROKERS_JSON`) {
+		t.Fatal("Docker config template must render Kafka brokers from KAFKA_BROKERS_JSON")
+	}
+	if strings.Contains(template, "kafka.118im.com:30835") {
+		t.Fatal("Docker config template must not hard-code the public Kafka NodePort")
+	}
+}