From ca8297a450c9047b105a52e6fc4f9021044df825 Mon Sep 17 00:00:00 2001
From: David Roberts <dave.roberts@elastic.co>
Date: Mon, 1 Nov 2021 14:59:31 +0000
Subject: [PATCH] [ML] Preserve alias attributes when making them hidden

This is a followup to #77416.

If aliases on ML hidden indices are made hidden then
all attributes of the alias need to be preserved.

The particularly critical case for ML is where a job's
results alias has a filter that restricts documents
returned when searching the shared results index to
those that relate to the job.
---
 .../xpack/ml/MlInitializationService.java     | 32 ++++++++++++-------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlInitializationService.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlInitializationService.java
index 3ddbdf04ffc1a..d22d768b242a4 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlInitializationService.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlInitializationService.java
@@ -177,19 +177,27 @@ private void makeMlInternalIndicesHidden() {
             IndicesAliasesRequest indicesAliasesRequest = new IndicesAliasesRequest();
             for (ObjectObjectCursor<String, List<AliasMetadata>> entry : getAliasesResponse.getAliases()) {
                 String index = entry.key;
-                String[] nonHiddenAliases = entry.value.stream()
-                    .filter(metadata -> metadata.isHidden() == null || metadata.isHidden() == false)
-                    .map(AliasMetadata::alias)
-                    .toArray(String[]::new);
-                if (nonHiddenAliases.length == 0) {
-                    continue;
-                }
-                indicesAliasesRequest.addAliasAction(
-                    IndicesAliasesRequest.AliasActions.add()
+                for (AliasMetadata existingAliasMetadata : entry.value) {
+                    if (existingAliasMetadata.isHidden() == null || existingAliasMetadata.isHidden() == false) {
+                        continue;
+                    }
+                    IndicesAliasesRequest.AliasActions addReplacementAliasAction = IndicesAliasesRequest.AliasActions.add()
                         .index(index)
-                        .aliases(entry.value.stream().map(AliasMetadata::alias).toArray(String[]::new))
-                        .isHidden(true)
-                );
+                        .aliases(existingAliasMetadata.getAlias())
+                        .writeIndex(existingAliasMetadata.writeIndex())
+                        .isHidden(true);
+                    // Be sure to preserve all attributes apart from is_hidden
+                    if (existingAliasMetadata.filteringRequired()) {
+                        addReplacementAliasAction.filter(existingAliasMetadata.getFilter().string());
+                    }
+                    if (existingAliasMetadata.indexRouting() != null) {
+                        addReplacementAliasAction.indexRouting(existingAliasMetadata.indexRouting());
+                    }
+                    if (existingAliasMetadata.searchRouting() != null) {
+                        addReplacementAliasAction.searchRouting(existingAliasMetadata.searchRouting());
+                    }
+                    indicesAliasesRequest.addAliasAction(addReplacementAliasAction);
+                }
             }
             if (indicesAliasesRequest.getAliasActions().isEmpty()) {
                 logger.debug("There are no ML internal aliases that need to be made hidden, [{}]", getAliasesResponse.getAliases());