Zero Downtime Reindexing & Unblocking in Elasticsearch

This is Part 6 of the "Building a Scalable, Faceted Online Marketplace" series. Read the Introduction here.

Why Zero Downtime Reindexing?

As your marketplace grows, you'll need to update mappings, add fields, or optimize your Elasticsearch indices. But how do you do this without taking your search offline? Enter zero-downtime reindexing and index unblocking.

The Tools: zero_downtime_reindex.js & unblock_index.js

• Clone and reindex your live index to a new one
• Switch aliases atomically to cut over with zero downtime
• Unblock a read-only index (e.g., after disk watermark issues)

Key Features

• Safe Reindexing: No lost queries, no downtime
• Alias Switching: Instantly swap old and new indices
• Unblock Utility: Quickly clear read-only status

Example Usage

node tools/zero_downtime_reindex.js --src products --dest products_v2 --es http://localhost:9200
node tools/unblock_index.js --index products --es http://localhost:9200

Real-World Tips

• Always test reindexing on a staging cluster first
• Monitor cluster health and alias status
• Use aliases for all production indices

Next up: Frontend: Meesho-Style Faceted Search UI in React

In the next article, we'll build a beautiful, responsive React UI for faceted search, just like Meesho or Amazon!