Trying to modify run.sh so it waits for the Xvfb server to start accepting connections.

Dockerfile

@@ -15,6 +15,7 @@ RUN apt-get -qq update \
     libprotobuf-dev \
     libxxf86vm-dev \
     xvfb \
+    netcat \
 && echo "deb https://deb.nodesource.com/node_6.x stretch main" >> /etc/apt/sources.list.d/nodejs.list \
 && echo "deb-src https://deb.nodesource.com/node_6.x stretch main" >> /etc/apt/sources.list.d/nodejs.list \
 && apt-get -qq update \

run.sh

@@ -1,9 +1,25 @@
 #!/bin/bash
 start-stop-daemon --start --pidfile ~/xvfb.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -screen 0 1024x768x24 -ac +extension GLX +render -noreset
 
-timeout 15 bash -c 'until echo > /dev/tcp/localhost/99; do sleep 0.5; done'
+let p=80
+while [ ${p} -lt 3000 ]
+ do
+    if nc -z localhost ${p}; then
+        let p+=1
+    else
+        let port=p
+        break
+    fi
+ done
+ echo The port is ${port}
 
-export DISPLAY=:99.0
+if ${port}; then
+    timeout 15 bash -c "until echo > /dev/tcp/localhost/${port}; do sleep 0.5; done"
+else
+    exit 1
+fi
+
+export DISPLAY=:${port}.0
 
 cd /data
 node /usr/src/app/ -p 80 "$@"