This tutorial series focuses specifically on tuning elasticsearch to achieve maximum indexing throughput and reduce monitoring and management load.
Elasticsearch provides sharding and replication as the recommended way for scaling and increasing availability of an index. A little over allocation is good but a bazillion shards is bad. It is difficult to define what constitutes too many shards, as it depends on their size and how they are being used. A hundred shards that are seldom used may be fine, while two shards experiencing very heavy usage could be too many. Monitor your nodes to ensure that they have enough spare capacity to deal with exceptional conditions.