Merge pull request #1594 from buildkite/fix/packer_base_ami_lookup

Author: scadu

.buildkite/steps/packer.sh

@@ -30,11 +30,23 @@ fi
 if [[ "${variant}" == "base" ]]; then
   make "packer-base-${os}-${arch}.output"
 else
-  # Require a golden base AMI from metadata
+  # Try metadata first, then S3 fallback for base AMI ID
   base_ami_id="$(buildkite-agent meta-data get "${os}-base-${arch}-ami" || true)"
 
   if [[ -z "$base_ami_id" ]]; then
-    echo "ERROR: No golden base AMI found for ${os}/${arch}. Ensure the corresponding base image step ran and uploaded the AMI ID." >&2
+    echo "Base AMI ID not found in metadata, checking S3 for latest base image..."
+
+    # Try to fetch the latest base AMI output from S3
+    latest_base_file="packer-base-${os}-${arch}-latest.output"
+    if aws s3 cp "s3://${BUILDKITE_AWS_STACK_BUCKET}/${latest_base_file}" "/tmp/${latest_base_file}" 2>/dev/null; then
+      base_ami_id=$(grep -Eo "${AWS_REGION}: (ami-.+)$" "/tmp/${latest_base_file}" | awk '{print $2}')
+      echo "Found base AMI ID from S3: $base_ami_id"
+      rm -f "/tmp/${latest_base_file}"
+    fi
+  fi
+
+  if [[ -z "$base_ami_id" ]]; then
+    echo "ERROR: No golden base AMI found for ${os}/${arch}. Ensure a base image has been built from main branch." >&2
     exit 1
   fi
 
@@ -43,6 +55,14 @@ fi
 
 # Upload to S3 with timestamped filename
 aws s3 cp "${local_output}" "s3://${BUILDKITE_AWS_STACK_BUCKET}/${packer_file}"
+
+# For base images on main branch, also upload as "latest"
+if [[ "${variant}" == "base" && "${BUILDKITE_BRANCH:-}" == "main" ]]; then
+  latest_file="packer-base-${os}-${arch}-latest.output"
+  aws s3 cp "${local_output}" "s3://${BUILDKITE_AWS_STACK_BUCKET}/${latest_file}"
+  echo "Updated latest base AMI pointer for ${os}/${arch}"
+fi
+
 mv "${local_output}" "${packer_file}"
 
 # Get the image id from the packer build output for later steps

packer/linux/.trigger-base-build

@@ -1 +1 @@
-# Last updated: 2025-09-18 12:56:38 UTC
+# Last updated: 2025-09-19 07:10:59 UTC

packer/windows/.trigger-base-build

@@ -1 +1 @@
-# Last updated: 2025-09-18 12:56:38 UTC
+# Last updated: 2025-09-19 07:10:59 UTC