Add forwards compatibility testing CI pipeline

(cherry picked from commit 6b1a6f7)

Author: mark-vieira

.buildkite/pipelines/periodic-fwc.template.yml

@@ -0,0 +1,15 @@
+steps:
+  - label: $FWC_VERSION / fwc
+    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
+    timeout_in_minutes: 300
+    agents:
+      provider: gcp
+      image: family/elasticsearch-ubuntu-2004
+      machineType: n1-standard-32
+      buildDirectory: /dev/shm/bk
+      preemptible: true
+    matrix:
+      setup:
+        FWC_VERSION: $FWC_LIST
+    env:
+      FWC_VERSION: $FWC_VERSION

.buildkite/pipelines/periodic-fwc.yml

@@ -0,0 +1,16 @@
+# This file is auto-generated. See .buildkite/pipelines/periodic-fwc.template.yml
+steps:
+  - label: $FWC_VERSION / fwc
+    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
+    timeout_in_minutes: 300
+    agents:
+      provider: gcp
+      image: family/elasticsearch-ubuntu-2004
+      machineType: n1-standard-32
+      buildDirectory: /dev/shm/bk
+      preemptible: true
+    matrix:
+      setup:
+        FWC_VERSION: []
+    env:
+      FWC_VERSION: $FWC_VERSION

.buildkite/scripts/branches.sh

@@ -2,3 +2,7 @@
 
 # This determines which branches will have pipelines triggered periodically, for dra workflows.
 BRANCHES=( $(cat branches.json | jq -r '.branches[].branch') )
+
+# Sort them to make ordering predictable
+IFS=$'\n' BRANCHES=($(sort <<<"${BRANCHES[*]}"))
+unset IFS

.buildkite/scripts/periodic.trigger.sh

@@ -46,4 +46,15 @@ EOF
       branch: "$BRANCH"
       commit: "$LAST_GOOD_COMMIT"
 EOF
+# Include forward compatibility tests only for the bugfix branch
+if [[ "${BRANCH}" == "${BRANCHES[2]}" ]]; then
+  cat <<EOF
+  - trigger: elasticsearch-periodic-fwc
+    label: Trigger periodic-fwc pipeline for $BRANCH
+    async: true
+    build:
+      branch: "$BRANCH"
+      commit: "$LAST_GOOD_COMMIT"
+EOF
+fi
 done

build.gradle

@@ -15,6 +15,7 @@ import com.fasterxml.jackson.databind.ObjectMapper
 
 import org.elasticsearch.gradle.DistributionDownloadPlugin
 import org.elasticsearch.gradle.Version
+import org.elasticsearch.gradle.VersionProperties
 import org.elasticsearch.gradle.internal.BaseInternalPluginBuildPlugin
 import org.elasticsearch.gradle.internal.ResolveAllDependencies
 import org.elasticsearch.gradle.util.GradleUtils
@@ -120,10 +121,10 @@ tasks.register("updateCIBwcVersions") {
     outputFile.text = "# This file is auto-generated. See ${pipelineTemplatePath}\n" + pipeline
   }
 
-  // Writes a Buildkite pipelime from a template, and replaces $BWC_LIST with an array of versions
+  // Writes a Buildkite pipelime from a template, and replaces a variable with an array of versions
   // Useful for writing a list of versions in a matrix configuration
-  def expandBwcList = { String outputFilePath, String pipelineTemplatePath, List<Version> versions ->
-    writeBuildkitePipeline(outputFilePath, pipelineTemplatePath, [new ListExpansion(versions: versions, variable: "BWC_LIST")])
+  def expandList = { String outputFilePath, String pipelineTemplatePath, String variable, List<Version> versions ->
+    writeBuildkitePipeline(outputFilePath, pipelineTemplatePath, [new ListExpansion(versions: versions, variable: variable)])
   }
 
   // Writes a Buildkite pipeline from a template, and replaces $BWC_STEPS with a list of steps, one for each version
@@ -140,11 +141,18 @@ tasks.register("updateCIBwcVersions") {
   doLast {
     writeVersions(file(".ci/bwcVersions"), filterIntermediatePatches(buildParams.bwcVersions.indexCompatible))
     writeVersions(file(".ci/snapshotBwcVersions"), filterIntermediatePatches(buildParams.bwcVersions.unreleasedIndexCompatible))
-    expandBwcList(
+    expandList(
       ".buildkite/pipelines/intake.yml",
       ".buildkite/pipelines/intake.template.yml",
+      "BWC_LIST",
       filterIntermediatePatches(buildParams.bwcVersions.unreleasedIndexCompatible)
     )
+    expandList(
+      ".buildkite/pipelines/periodic-fwc.yml",
+      ".buildkite/pipelines/periodic-fwc.template.yml",
+      "FWC_LIST",
+      buildParams.bwcVersions.released.findAll { it.major == VersionProperties.elasticsearchVersion.major && it.minor == VersionProperties.elasticsearchVersion.minor }
+    )
     writeBuildkitePipeline(
       ".buildkite/pipelines/periodic.yml",
       ".buildkite/pipelines/periodic.template.yml",