Connecting a remote shell to a GAE app

I’m trying to connect a remote shell to a running GAE elixir app. The app is running fine, when I try to connect I get this:

Could not contact remote node the_kraken@aef-default-20200421t125549-782j.europe-west2-b.c.quick-cogency-270011.internal, reason: :nodedown. Aborting...

I am using mix releases, the hostname is correct AFAICT because it comes from a request to google. How can I get more info about what nodedown means?

My looks like this if that helps:


# Set the release to work across nodes. If using the long name format like
# the one below (my_app@, you need to also uncomment the
# RELEASE_DISTRIBUTION variable below. Must be "sname", "name" or "none".
export RELEASE_NODE=<%= %>@${HOSTNAME}

When should NODE_COOKIE be set?