enable configurable RUM destination in frontend

src/frontend/Dockerfile

@@ -23,14 +23,15 @@ RUN npm run grpc:generate
 RUN npm run build
 
 FROM node:18-alpine AS runner
+RUN addgroup -g 1001 -S nodejs
+RUN adduser -S nextjs -u 1001
+
 WORKDIR /app
+RUN chown nextjs /app
 RUN apk add --no-cache protobuf-dev protoc
 
 ENV NODE_ENV=production
 
-RUN addgroup -g 1001 -S nodejs
-RUN adduser -S nextjs -u 1001
-
 COPY --from=builder /app/next.config.js ./
 COPY --from=builder /app/utils/telemetry/Instrumentation.js ./
 COPY --from=builder /app/public ./public
@@ -39,6 +40,7 @@ COPY --from=deps /app/node_modules ./node_modules
 
 COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
 COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
+COPY --from=builder --chown=nextjs:nodejs /app/config_rum_and_start .
 
 USER nextjs
 

src/frontend/config_rum_and_start

@@ -0,0 +1,53 @@
+chunksDir=/app/.next/static/chunks
+envFile=/app/splunk_rum_env
+
+noRumStart() {
+    echo "Frontend starting with no RUM support."
+    echo "You will probably see browser console errors."
+    cd /app
+    npm start
+    exit
+}
+
+
+if ! [ -f $envFile ]; then
+    echo "Config file \"$envFile\" for Splunk Rum not found."
+    noRumStart
+fi
+
+# Splunk Rum config file found.  Try to substitute SPLUNK_RUM_PLACEHOLDER values
+cd $chunksDir
+mainfile=$(ls main-*.js)
+
+if [ "$mainfile" == '' ] ; then
+  # Next.js main chunk file not found
+  echo "Did not find main file in $chunksDir"
+  noRumStart
+fi
+
+if echo "$mainfile" | grep -q ' ' ; then
+  # Uh-oh, got multiple mainfiles.  
+  echo "Found multiple main files in $chunksDir"
+  noRumStart
+fi
+
+echo splunk_rum_env file contains the following values:
+cat $envFile
+. $envFile
+sed -e "s/SPLUNK_RUM_REALM_PLACEHOLDER/$SPLUNK_RUM_REALM/" \
+    -e "s/SPLUNK_RUM_TOKEN_PLACEHOLDER/$SPLUNK_RUM_TOKEN/" \
+    -e "s/SPLUNK_RUM_APP_PLACEHOLDER/$SPLUNK_RUM_APP_NAME/" \
+    -e "s/SPLUNK_RUM_ENV_PLACEHOLDER/$SPLUNK_RUM_ENV/"  < $mainfile > /tmp/${mainfile}.new
+
+if [ "$?" -ne 0 ]; then
+    # Some error while running the sed command. Do a fallback start
+    echo "Encountered an error while trying to substitute RUM config placeholders"
+    noRumStart
+fi
+
+# All looks good! We should be able to do a regular start
+cp ${mainfile} /tmp/$mainfile.orig
+cp /tmp/${mainfile}.new $mainfile
+cd /app
+npm start
+

src/frontend/splunk-rum.js

@@ -1,15 +1,15 @@
 import SplunkRum from '@splunk/otel-web';
 
 SplunkRum.init({
-    realm: "us1",
-    rumAccessToken: "5UxP7X9NINTxugmccK8kaA",
-    applicationName: "astroshop_lab",
-    deploymentEnvironment: "astroshop_lab"
+    realm: "SPLUNK_RUM_REALM_PLACEHOLDER",
+    rumAccessToken: "SPLUNK_RUM_TOKEN_PLACEHOLDER",
+    applicationName: "SPLUNK_RUM_APP_PLACEHOLDER",
+    deploymentEnvironment: "SPLUNK_RUM_ENV_PLACEHOLDER"
 });
 
 //SplunkRum.init({
 //    realm: "us1",
 //    rumAccessToken: "Qad35m7E6ld6p_-O_RxwEg",
-//    applicationName: "astroshop",
-//    deploymentEnvironment: "astroshop"
+//    applicationName: "astroshop_lab_2",
+//    deploymentEnvironment: "astroshop_lab_2"
 //});