build: add Loki CI step to eui-pull-request-and-deploy pipeline

.buildkite/pipelines/pipeline_pull_request_test_and_deploy.yml

@@ -2,15 +2,32 @@
 
 steps:
   - trigger: "eui-pull-request-test"
+    key: "test"
     label: ":hammer: EUI pull request test"
     build:
       branch: "${BUILDKITE_BRANCH}"
       commit: "${BUILDKITE_COMMIT}"
   - trigger: "eui-pull-request-deploy-docs"
+    key: "deploy-docs"
     label: ":newspaper: EUI pull request deploy docs"
     build:
       branch: "${BUILDKITE_BRANCH}"
       commit: "${BUILDKITE_COMMIT}"
       env:
         GIT_BRANCH: "${BUILDKITE_BRANCH}"
         GIT_PULL_REQUEST_ID: "${BUILDKITE_PULL_REQUEST}"
+  - depends_on: "deploy-docs"
+    label: ":camera_with_flash: Visual regression tests"
+    command: ".buildkite/scripts/visual_regression/run_loki.sh"
+    agents:
+      provider: "gcp"
+      # Loki isn't resource heavy and doesn't benefit
+      # from faster CPUs like the n2 family
+      machineType: 'n1-standard-1'
+      # Use spot instances
+      # https://cloud.google.com/spot-vms
+      preemptible: true
+    retry:
+      automatic:
+        - exit_status: '-1'
+          limit: 1

.buildkite/scripts/visual_regression/run_loki.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+set -euo pipefail
+
+storybook_url="https://eui.elastic.co/storybook"
+
+# If the branch is not a pull request, Buildkite passes "false"
+# https://buildkite.com/docs/pipelines/environment-variables#BUILDKITE_PULL_REQUEST
+if [[ "${BUILDKITE_PULL_REQUEST}" != "false" ]]; then
+  echo "+++ Running visual regression tests on pull request #${BUILDKITE_PULL_REQUEST}"
+  echo "https://github.com/elastic/eui/pull/${BUILDKITE_PULL_REQUEST}"
+  storybook_url="https://eui.elastic.co/pr_${BUILDKITE_PULL_REQUEST}/storybook"
+elif [[ "${BUILDKITE_BRANCH}" == "main" ]]; then
+  echo "+++ Running visual regression tests on main"
+else
+  echo "+++ :x: Visual regression tests can only be run against \`main\` and open pull requests. Exiting"
+  exit 1
+fi
+
+docker run \
+  -i \
+  --rm \
+  --env GIT_COMMITTER_NAME=test \
+  --env GIT_COMMITTER_EMAIL=test \
+  --env HOME=/tmp \
+  --user="$(id -u):$(id -g)" \
+  --volume="$(pwd):/app" \
+  --workdir=/app \
+  "$DOCKER_BASE_IMAGE" \
+  bash -c "yarn && yarn --cwd packages/eui test-visual-regression --reactUri $storybook_url"