How to fix InvalidIndexNameException: Invalid index name [INDEX], must be lowercase in Elasticsearch

InvalidIndexNameException: Invalid index name [MyIndex], must be lowercase

# Before (causes error)
curl -X PUT "localhost:9200/MyIndex"

# After (works correctly)
curl -X PUT "localhost:9200/myindex"

// Before
const indexName = "UserData";
await client.indices.create({ index: indexName });

// After
const indexName = "userdata";
// Or dynamically convert
const indexName = "UserData".toLowerCase();
await client.indices.create({ index: indexName });

# Before
index_name = "MyIndex"

# After
index_name = "myindex"
# Or
index_name = "MyIndex".lower()

# Invalid: uppercase letters
MyIndex, TEST, User-Data

# Invalid: starts with hyphen, underscore, or plus
-myindex, _myindex, +myindex

# Invalid: contains spaces
my index, user data

# Invalid: contains special characters
my*index, my#index, my?index, my/index

# Invalid: contains backslash, comma, angle brackets, pipe, quotes
my\index, my,index, my<index, my|index, "myindex"

# Valid examples
myindex, user-data, logs-2024, app_metrics

PUT _index_template/logs-template
{
  "index_patterns": ["logs-*"],
  "template": {
    "settings": {
      "number_of_shards": 1
    },
    "mappings": {
      "properties": {
        "@timestamp": { "type": "date" }
      }
    }
  }
}

output {
  elasticsearch {
    hosts => ["localhost:9200"]
    # Use lowercase with date pattern
    index => "logs-%{+yyyy.MM.dd}"
    # Avoid: index => "Logs-%{+yyyy.MM.dd}"
  }
}

output.elasticsearch:
  hosts: ["localhost:9200"]
  # Use lowercase
  index: "filebeat-%{[agent.version]}-%{+yyyy.MM.dd}"

function validateIndexName(name: string): string {
  // Convert to lowercase
  let validName = name.toLowerCase();

  // Replace invalid characters with hyphens
  validName = validName.replace(/[^a-z0-9_-]/g, '-');

  // Remove leading special characters
  validName = validName.replace(/^[_+-]+/, '');

  // Ensure not just dots
  if (/^.+$/.test(validName)) {
    throw new Error('Index name cannot consist only of dots');
  }

  // Check length
  if (validName.length > 255) {
    validName = validName.substring(0, 255);
  }

  return validName;
}

// Usage
const userInput = "MyIndex";
const safeName = validateIndexName(userInput);
await client.indices.create({ index: safeName });

import re

def validate_index_name(name: str) -> str:
    # Convert to lowercase
    valid_name = name.lower()

    # Replace invalid characters
    valid_name = re.sub(r'[^a-z0-9_-]', '-', valid_name)

    # Remove leading special characters
    valid_name = re.sub(r'^[_+-]+', '', valid_name)

    # Check if only dots
    if re.match(r'^.+$', valid_name):
        raise ValueError("Index name cannot consist only of dots")

    # Truncate if too long
    if len(valid_name.encode('utf-8')) > 255:
        valid_name = valid_name[:255]

    return valid_name

# Usage
user_input = "MyIndex"
safe_name = validate_index_name(user_input)
es.indices.create(index=safe_name)

# Create the lowercase index
PUT /myindex

# Create an alias with a similar name (must also be lowercase)
POST /_aliases
{
  "actions": [
    {
      "add": {
        "index": "myindex",
        "alias": "my-index-alias"
      }
    }
  ]
}

# In a Git repository
git grep -i "MyIndex"

# Update all references to use lowercase