Implementing Custom Conflict Resolution with Azure Functions for Multi-Master Writes

When LWW (Last Writer Wins) is insufficient, use a Stored Procedure for custom merge logic, triggered when conflicting updates occur in different regions.

In Multi-Master (Multi-Region Write) setups, conflicts occur when two regions update the same document simultaneously. By default, Cosmos DB uses LWW (based on the _ts timestamp). However, for complex business logic, you can define a 'Custom Conflict Resolution' policy. This requires a JavaScript Stored Procedure that receives the conflicting versions. The procedure must decide which version wins or create a merged version. Note: This procedure runs locally in the region where the conflict is being resolved.