With our continued focus on automation,  the @PhonePe SRE team recently automated the entire flow for rolling upgrades to Elasticsearch. With each node approximately at 2.5TB and clusters of 400 to 500 nodes, a single cluster can be more than 1 petabyte. Add to that multiple clusters across datacenters for redundancy and the problem of upgrades becomes a massive undertaking . Here is an insightful blog on how PhonePe SREs automated this entire flow, helping us eliminate downtime and reduce upgrade times from 10 hours to 4 - 6 hours with minimal involvement by an engineer for not more than 30 mins