cancel build if there’s a queue

Author: bmorelli25

.buildkite/build_pipeline.yml

@@ -24,6 +24,10 @@ steps:
           - label: "Fail the build"
             value: ""
         hint: "Should we ignore checking broken links? Should we allow to run the build without failing if there's a broken link? Ignoring broken links is dangerous not just because bad links will leak into the public site but because subsequent builds and pull requests that do not fix the links fail."
+  - wait
+  - label: "Check for queue"
+    if: build.source == "schedule"
+    command: ".buildkite/scripts/check_queue.sh"
     concurrency: 1
     concurrency_group: docs-build-${BUILDKITE_BRANCH}
   - wait

.buildkite/scripts/check_queue.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+last_build_url="https://api.buildkite.com/v2/organizations/elastic/pipelines/${BUILDKITE_PIPELINE_SLUG}/builds?branch=${BUILDKITE_BRANCH}"
+cancel_build_url="https://api.buildkite.com/v2/organizations/elastic/pipelines/${BUILDKITE_PIPELINE_SLUG}/builds/${BUILDKITE_JOB_ID}/cancel"
+
+LAST_BUILD_STATE=$(curl -s -H "Authorization: Bearer ${BUILDKITE_API_TOKEN}" $last_successful_build_url | jq -r '.[1].status')
+
+echo "Determining if the last build is currently blocked."
+if [[ "$LAST_BUILD_STATE" == "blocked" ]]; then
+  echo "The pipeline is congested. Canceling this build."
+  curl -sX PUT -H "Authorization: Bearer ${BUILDKITE_API_TOKEN}" $cancel_build_url
+else
+  echo "The pipeline is ready for a new build."
+fi