stdlib/aws: implemented elb helper to get a free RulePriority from a load balancer

Signed-off-by: Sam Alba <sam.alba@gmail.com>

stdlib/aws/elb/elb.cue

@@ -0,0 +1,66 @@
+package elb
+
+import (
+	"dagger.io/aws"
+)
+
+// Returns a non-taken rule priority (randomized)
+#RandomRulePriority: {
+	// AWS Config
+	config: aws.#Config
+
+	// ListenerArn
+	listenerArn: string
+
+	// Optional vhost for reusing priorities
+	vhost?: string
+
+	aws.#Script & {
+		files: {
+			"/inputs/aws/access_key": config.accessKey
+			"/inputs/aws/secret_key": config.secretKey
+			"/inputs/listenerArn":    listenerArn
+			if vhost != _|_ {
+				"/inputs/vhost":          vhost
+			}
+		}
+
+		export: "/priority"
+
+		//FIXME: The code below can end up not finding an available prio
+		// Better to exclude the existing allocated priorities from the random sequence
+		code: #"""
+			if [ -s /inputs/vhost ]; then
+				# We passed a vhost as input, try to recycle priority from previously allocated vhost
+				vhost="$(cat /inputs/vhost)"
+
+				priority=$(aws elbv2 describe-rules \
+					--listener-arn "$(cat /inputs/listenerArn)" | \
+					jq -r --arg vhost "$vhost" '.Rules[] | select(.Conditions[].HostHeaderConfig.Values[] == $vhost) | .Priority')
+
+				if [ -n "${priority}" ]; then
+					echo -n "${priority}" > /priority
+					exit 0
+				fi
+			fi
+
+			# Grab a priority random from 1-50k and check if available, retry 10 times if none available
+			priority=0
+			for i in {1..10}
+			do
+				p=$(shuf -i 1-50000 -n 1)
+				# Find the next priority available that we can allocate
+				aws elbv2 describe-rules \
+					--listener-arn "$(cat /inputs/listenerArn)" \
+					| jq -e "select(.Rules[].Priority == \"${p}\") | true" && continue
+				priority="${p}"
+				break
+			done
+			if [ "${priority}" -lt 1 ]; then
+				echo "Error: cannot determine a Rule priority"
+				exit 1
+			fi
+			echo -n "${priority}" > /priority
+			"""#
+	}
+}