Why etcd? Why not some SQL or NoSQL database?

When chosen as the data store etcd was (and still is of course):

• Highly Available - you can deploy multiple nodes
• Fully Replicated - any node in etcd cluster is "primary" node and has full access to the data
• Consistent - reads return latest data
• Secured - supports both TLS and SSL
• Speed - high performance data store (10k writes per sec!)