A computer-implemented method, comprising: determining to add a new database, DB, node to a cluster of one or more DB nodes implementing a database in a database service, wherein the cluster includes a first DB node of a compute tier of the database service; and scaling the cluster of one or more DB nodes to add at least the new DB node, comprising: determining a split for data, of a first volume, managed by the first DB node, the split including a first portion of the data to remain managed by first DB node and a second portion of the data to be managed by the new DB node; obtaining a second DB node, in the compute tier, to serve as the new DB node; cloning the first volume, within a storage tier that is distinct from the compute tier, to yield a second volume for use by the second DB node of the compute tier, wherein cloning the first volume to yield the second volume comprises creating, as the second volume, a copy-on-write volume based on creating one or more metadata elements for the second volume that identify the data of the first volume, wherein the copy-on-write volume does not include a distinct copy of the data of the first volume; applying, after the cloning, a set of database modifications to the second volume, where the set of database modifications resulted from database traffic received by the first DB node, involving the second portion, during the cloning of the first volume; and updating a proxy layer to begin sending database traffic involving the second portion of the data to the second DB node of the compute tier, wherein during or after the cloning of the first volume, but prior to the updating of the proxy layer, the method further comprises, if a request is received at the first DB node involving the second portion of data that is to be managed by the new DB node, sending a response message to the proxy layer indicating that the request is denied, wherein the response message indicates that the request can be retried, and wherein the response message further includes a routing value allowing the proxy layer to update its routing cache to send additional requests involving the second portion of data to the second DB node. determining to add a new database, DB, node to a cluster of one or more DB nodes implementing a database in a database service, wherein the cluster includes a first DB node of a compute tier of the database service; and scaling the cluster of one or more DB nodes to add at least the new DB node, comprising: determining a split for data, of a first volume, managed by the first DB node, the split including a first portion of the data to remain managed by first DB node and a second portion of the data to be managed by the new DB node; obtaining a second DB node, in the compute tier, to serve as the new DB node; cloning the first volume, within a storage tier that is distinct from the compute tier, to yield a second volume for use by the second DB node of the compute tier, wherein cloning the first volume to yield the second volume comprises creating, as the second volume, a copy-on-write volume based on creating one or more metadata elements for the second volume that identify the data of the first volume, wherein the copy-on-write volume does not include a distinct copy of the data of the first volume; applying, after the cloning, a set of database modifications to the second volume, where the set of database modifications resulted from database traffic received by the first DB node, involving the second portion, during the cloning of the first volume; and updating a proxy layer to begin sending database traffic involving the second portion of the data to the second DB node of the compute tier, determining a split for data, of a first volume, managed by the first DB node, the split including a first portion of the data to remain managed by first DB node and a second portion of the data to be managed by the new DB node; obtaining a second DB node, in the compute tier, to serve as the new DB node; cloning the first volume, within a storage tier that is distinct from the compute tier, to yield a second volume for use by the second DB node of the compute tier, wherein cloning the first volume to yield the second volume comprises creating, as the second volume, a copy-on-write volume based on creating one or more metadata elements for the second volume that identify the data of the first volume, wherein the copy-on-write volume does not include a distinct copy of the data of the first volume; applying, after the cloning, a set of database modifications to the second volume, where the set of database modifications resulted from database traffic received by the first DB node, involving the second portion, during the cloning of the first volume; and updating a proxy layer to begin sending database traffic involving the second portion of the data to the second DB node of the compute tier, wherein during or after the cloning of the first volume, but prior to the updating of the proxy layer, the method further comprises, if a request is received at the first DB node involving the second portion of data that is to be managed by the new DB node, sending a response message to the proxy layer indicating that the request is denied, wherein the response message indicates that the request can be retried, and wherein the response message further includes a routing value allowing the proxy layer to update its routing cache to send additional requests involving the second portion of data to the second DB node.