sandbox: add env:flex configuration file

vm: true is going away and less stable.
Add an alternate configuration file that uses the new App Engine
flexible environment.

NOTE: the new environment currently has vastly different network
configuration, so it's important it's hosted at a different URL for now.
The module name is changed to "sandbox-flex" to reflect this.

Change-Id: Iec3ed9bdb1d61f6aafd26350a01ad268adf3194e
Reviewed-by: Brad Fitzpatrick <>
diff --git a/sandbox/app-flex.yaml b/sandbox/app-flex.yaml
new file mode 100644
index 0000000..b9501dc
--- /dev/null
+++ b/sandbox/app-flex.yaml
@@ -0,0 +1,7 @@
+service: sandbox-flex
+runtime: custom
+env: flex
+  check_interval_sec: 20
+  restart_threshold: 10