Prevent pinning writes in non-primary DCs

lib/deployment.rb

@@ -0,0 +1 @@
+require_relative "deployment/database_resolver.rb"

lib/deployment/database_resolver.rb

@@ -0,0 +1,18 @@
+module Deployment
+  class DatabaseResolver < ActiveRecord::Middleware::DatabaseSelector::Resolver
+    def self.in_primary_datacenter?
+      ENV["PRIMARY_DATACENTER"].present? || Rails.env.local?
+    end
+
+    def reading_request?(request)
+      # Disables writes (and so primary-DB stickiness) in non-primary datacenters
+      super || !DatabaseResolver.in_primary_datacenter?
+    end
+
+    private
+      def read_from_primary?
+        # Only the primary datacenter can read from the primary database, non-primary DCs have local DB replicas
+        super && DatabaseResolver.in_primary_datacenter?
+      end
+  end
+end