[9.0] [CI] Clear EPR cached docker image in an EPR cache verification scenario (elastic#235187) (elastic#235245)

# Backport

This will backport the following commits from `main` to `9.0`:
- [[CI] Clear EPR cached docker image in an EPR cache verification
scenario (elastic#235187)](elastic#235187)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Alex
Szabo","email":"[email protected]"},"sourceCommit":{"committedDate":"2025-09-16T16:12:46Z","message":"[CI]
Clear EPR cached docker image in an EPR cache verification scenario
(elastic#235187)\n\n## Summary\nWe've been getting errors about running out of
disk space in EPR image\nvalidation pipelines.\n\nIn those pipelines, we
are pulling a new version of EPR, that together\nwith the VM-cached
image will deplete our disk in several cases. This PR\nadds an
executor-setup step at buildkite's pre-command hook that would\nclear
the cache, and make room for the validated image.\n\nCorrect behavior
(without FTR retries) can be observed
here:\nhttps://buildkite.com/elastic/kibana-package-registry-verify-and-promote/builds/276#_","sha":"15640633f4997245c8695ac1a59c10e275068d79","branchLabelMapping":{"^v9.2.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Operations","release_note:skip","backport:all-open","v9.2.0"],"title":"[CI]
Clear EPR cached docker image in an EPR cache verification
scenario","number":235187,"url":"https://github.com/elastic/kibana/pull/235187","mergeCommit":{"message":"[CI]
Clear EPR cached docker image in an EPR cache verification scenario
(elastic#235187)\n\n## Summary\nWe've been getting errors about running out of
disk space in EPR image\nvalidation pipelines.\n\nIn those pipelines, we
are pulling a new version of EPR, that together\nwith the VM-cached
image will deplete our disk in several cases. This PR\nadds an
executor-setup step at buildkite's pre-command hook that would\nclear
the cache, and make room for the validated image.\n\nCorrect behavior
(without FTR retries) can be observed
here:\nhttps://buildkite.com/elastic/kibana-package-registry-verify-and-promote/builds/276#_","sha":"15640633f4997245c8695ac1a59c10e275068d79"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.2.0","branchLabelMappingKey":"^v9.2.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/235187","number":235187,"mergeCommit":{"message":"[CI]
Clear EPR cached docker image in an EPR cache verification scenario
(elastic#235187)\n\n## Summary\nWe've been getting errors about running out of
disk space in EPR image\nvalidation pipelines.\n\nIn those pipelines, we
are pulling a new version of EPR, that together\nwith the VM-cached
image will deplete our disk in several cases. This PR\nadds an
executor-setup step at buildkite's pre-command hook that would\nclear
the cache, and make room for the validated image.\n\nCorrect behavior
(without FTR retries) can be observed
here:\nhttps://buildkite.com/elastic/kibana-package-registry-verify-and-promote/builds/276#_","sha":"15640633f4997245c8695ac1a59c10e275068d79"}}]}]
BACKPORT-->

Co-authored-by: Alex Szabo <[email protected]>

Author: kibanamachine

.buildkite/scripts/common/setup_executors.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Executor-related setup
+
+echo '--- Executor Setup'
+
+# if FLEET_PACKAGE_REGISTRY_DOCKER_IMAGE is set,
+# we should clear previously cached EPR images,
+# (as the package registry image is quite big to keep 2 versions of)
+DEFAULT_FLEET_PACKAGE_REGISTRY_DOCKER_IMAGE='docker.elastic.co/kibana-ci/package-registry-distribution:lite'
+
+# Test docker is available
+if [[ `command -v docker` \
+      && -n "${FLEET_PACKAGE_REGISTRY_DOCKER_IMAGE:-}" \
+      && "${FLEET_PACKAGE_REGISTRY_DOCKER_IMAGE}" != "${DEFAULT_FLEET_PACKAGE_REGISTRY_DOCKER_IMAGE}" \
+]]; then
+  echo 'Clearing previously cached EPR images'
+  EPR_IMAGES=$(docker images -q "${DEFAULT_FLEET_PACKAGE_REGISTRY_DOCKER_IMAGE}")
+  if [[ -n "${EPR_IMAGES}" ]]; then
+    docker rmi -f "${EPR_IMAGES}"
+    echo "Cleared ${EPR_IMAGES} EPR images"
+  fi
+fi

.buildkite/scripts/lifecycle/pre_command.sh

@@ -5,6 +5,7 @@ set -euo pipefail
 source .buildkite/scripts/common/util.sh
 source .buildkite/scripts/common/env.sh
 source .buildkite/scripts/common/setup_job_env.sh
+source .buildkite/scripts/common/setup_executors.sh
 
 if [[ "${SKIP_NODE_SETUP:-}" =~ ^(1|true)$ ]]; then
   echo "Skipping node setup (SKIP_NODE_SETUP=$SKIP_NODE_SETUP)"