Use latest function metadata to check cached function service. (#316)

Watch functions in the router and use that to trigger functionReferenceResolver cache invalidation.

We might want to rate-limit syncTriggers in a future change, since we might be triggering it more often than needed.

test/tests/test_function_update.sh

@@ -0,0 +1,62 @@
+#!/bin/bash
+
+set -euo pipefail
+
+ROOT=$(dirname $0)/../..
+
+fn=nodejs-hello-$(date +%s)
+
+# Create a function in nodejs, test it with an HTTP trigger.
+# Update it and check it's output, the output should be 
+# different from the previous one.
+
+echo "Pre-test cleanup"
+fission env delete --name nodejs || true
+
+echo "Creating nodejs env"
+fission env create --name nodejs --image fission/node-env
+trap "fission env delete --name nodejs" EXIT
+
+echo "Creating function"
+echo 'module.exports = function(context, callback) { callback(200, "foo!\n"); }' > foo.js
+fission fn create --name $fn --env nodejs --code foo.js
+trap "fission fn delete --name $fn" EXIT
+
+echo "Creating route"
+fission route create --function $fn --url /$fn --method GET
+
+echo "Waiting for router to catch up"
+sleep 10
+
+echo "Doing an HTTP GET on the function's route"
+response=$(curl http://$FISSION_ROUTER/$fn)
+
+echo "Checking for valid response"
+echo $response | grep -i foo
+
+# Running a background process to keep access the
+# function to emulate real online traffic. The router
+# should be able to update cache under this situation.
+( watch -n1 curl http://$FISSION_ROUTER/$fn ) > /dev/null 2>&1 &
+pid=$!
+
+echo "Updating function"
+echo 'module.exports = function(context, callback) { callback(200, "bar!\n"); }' > bar.js
+fission fn update --name $fn --code bar.js
+trap "fission fn delete --name $fn" EXIT
+
+echo "Waiting for router to update cache"
+sleep 10
+
+echo "Doing an HTTP GET on the function's route"
+response=$(curl http://$FISSION_ROUTER/$fn)
+
+echo "Checking for valid response again"
+echo $response | grep -i bar
+
+kill -15 $pid
+
+# crappy cleanup, improve this later
+kubectl get httptrigger -o name | tail -1 | cut -f2 -d'/' | xargs kubectl delete httptrigger
+
+echo "All done."