elastic/elasticsearch

CCR automatically replicates all x-pack index settings

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#51,972 opened on Feb 6, 2020

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 (13 comments) (0 reactions) (0 assignees)Java (76,700 stars) (25,882 forks)batch import
:Distributed/CCR>bugTeam:Distributedhelp wanted

Description

CCR is deliberate about which index settings it copies:

https://github.com/elastic/elasticsearch/blob/da20957e815d9370142738be9e402727f36b9857/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowAction.java#L455-L460

In fact, there is a test to ensure that if any index setting is added, the setting is either deliberately marked as replicated, or is added to the list of non-replicated settings:

https://github.com/elastic/elasticsearch/blob/698b1e97e78cdec26f1b2f971dd0d5e79e8ac47e/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowActionTests.java#L198-L222

Alas, there is some oversight here which relates to index settings registered in x-pack (e.g., ILM index-level settings such as the index policy). This means that today, all such settings are replicated from the leader to the follower. This can lead to issues on the follower (e.g., explicit issues such as if the ILM policy does not exist in the local cluster, or implicit issues such as if the ILM policy does exist in the local cluster, but it's not the one that user wanted to have used on the follower index).

Contributor guide

Tech stack
java
Domain
backenddatabase
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Elasticsearch internalsCCR plugin codeIndex settings management
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the list of non replicated settings in TransportResumeFollowAction.java and identify which x pack index settings (e.g., ILM policy) are missing from that list. Then, modify the code to exclude all such settings or add them to the non replicated list. The test in TransportResumeFollowActionTests.java can be used to ensure no new settings slip through.