What is the difference between index and create operations?

The index operation writes a document whether or not its ID already exists, while the create operation writes it only if the ID is new.

• Index, PUT /index/_doc/id, creates a new document or replaces the entire existing one. Each replace increments the document's _version.
• Create, PUT /index/_create/id, only creates a new document. If a document with the same ID exists, it fails with a 409 Conflict error. The index API gives the same check with op_type=create.

Use create when a duplicate ID would be a bug, such as writing events that must be stored once. Use index when the latest version should win.

# Index - will replace if exists
PUT /users/_doc/1
{"name": "John", "age": 30}

# Create - will fail if ID 1 exists
PUT /users/_create/1
{"name": "Jane", "age": 25}

Run in this order, the second request fails, because the first one already wrote ID 1.