sets slave port as docker needs to map ahead of time
diff --git a/init.groovy b/init.groovy
new file mode 100644
index 0000000..d13f089
--- /dev/null
+++ b/init.groovy
@@ -0,0 +1,5 @@
+import hudson.model.*;
+import jenkins.model.*;
+
+println "--> setting agent port for jnlp"
+Jenkins.instance.setSlaveAgentPort(50000)