Dest index must be lowercase – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 7.3-7.5

Briefly, this error occurs when the destination index name in Elasticsearch is not in lowercase. Elasticsearch requires all index names to be in lowercase. This is a built-in validation to prevent issues that could arise from case-sensitive index names. To resolve this issue, you should rename your index to a lowercase name. You can do this by reindexing your data into a new index with a lowercase name, or by creating an alias with a lowercase name that points to your existing index.

This guide will help you check for common problems that cause the log ” dest.index must be lowercase ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “dest.index must be lowercase” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 public void validate() {
 if (index != null) {
 validateIndexOrAliasName(index; InvalidIndexNameException::new);
 if (index.toLowerCase(Locale.ROOT).equals(index) == false) {
 throw new InvalidIndexNameException(index; "dest.index must be lowercase");


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