Added some comments about sequencing for implementation

doc/controller.md

@@ -43,6 +43,10 @@ This means that co-ordination is required across nodes for some (or all) tasks s
 Some of that co-ordination could be done with the current sidecar approach.
 But many of them, especially, restoration and scaling are done better with a controller.
 
+For backups, a better option might be to separate the backup sidecar as a separate pod for the whole etcd cluster rather than a sidecar container for each etcd instance in the etcd cluster.
+This could be optionally used only in the multi-node scenario and we can perhaps continue to use the sidecar container approach for the single-node scenarion.
+This could be the first step and we can think of introducing the controller for co-ordination for other life-cycle operations.
+
 ## Database Restoration
 
 Database restoration is also currently done on startup (or a restart) (if database verification fails) within the same backup-restore sidecar's main process.
@@ -51,6 +55,8 @@ Introducing a controller enables the option to perform database restoration as a
 The main advantage of this approach is to decouple the memory requirement of a database restoration from the regular backup (full and delta) tasks.
 This could be especially of interest because the delta snapshot restoration requires an embedded `etcd` instance which might mean that the memory requirement for database restoration is almost certain to be proportionate to the database size. However, the memory requirement for backup (full and delta) need not be proportionate to the database size at all. In fact, it is very realistic to expect that the memory requirement for backup be more or less independent of the database size.
 
+This could be a second step because we can introduce only a lean controller for restoration and this might even be possible to do this without introducing a CRD.
+
 ## Database Incremental Backup Compaction
 
 Incremental/continuous backup is used for finer granularity backup (in the order of minutes) with full snapshots being taken at a much larger intervals (in the order of hours). This makes the backup efficient both in terms of disk, network bandwidth and backup storage space utilization as well as compute resource utilization during backup.
@@ -59,6 +65,8 @@ However, if the proportion of changes in the incremental backup is large then th
 
 A controller can be used to periodically perform compaction of the incremental backups in the backup storage. This can optimize both the restoration times as well as the backup storage space utilization while not affecting the regular backup performance because such compaction would be done asynchronously.
 
+This feature could be implemented as an enhancement of the [database restoration](#database-restoration) functionality.
+
 ## Database Verification
 
 Database verification is currently done on startup (or a restart) within the same backup-restore sidecar's main process.