SkyDNS vs SmartStack: What are the differences?

What is SkyDNS? Distributed service for announcement and discovery of services. SkyDNS is a distributed service for announcement and discovery of services. It leverages Raft for high-availability and consensus, and utilizes DNS queries to discover available services. This is done by leveraging SRV records in DNS, with special meaning given to subdomains, priorities and weights (more info here: http://blog.gopheracademy.com/skydns).

What is SmartStack? Automated service discovery and registration framework. Scaling a web infrastructure requires services, and building a service-oriented infrastructure is hard. Make it EASY, with SmartStack’s automated, transparent service discovery and registration: cruise control for your distributed infrastructure.

SkyDNS and SmartStack can be categorized as "Open Source Service Discovery" tools.

Some of the features offered by SkyDNS are:

• You announce your service by submitting JSON over HTTP to SkyDNS with information about your service. This information will then be available for queries either via DNS or HTTP.
• SkyDNS requires that services submit an HTTP request to update their TTL within the TTL they last supplied. If the service fails to do so within this timeframe SkyDNS will expire the service automatically. This will allow for nodes to fail and DNS to reflect this quickly.
• You can find services by querying SkyDNS via any DNS client or utility. It uses a known domain syntax with wildcards to find matching services.

On the other hand, SmartStack provides the following key features:

• Within a health check interval’s delay of a backend becoming healthy, it is made available in Zookeeper
• this makes it instantly available to consumers via Synapse’s Zookeeper watches.
• We detect problems within a health check interval, and take backends out of rotation. A mechanism which allows services to notify Nerve that they’re not healthy is planned, to reduce the interval further. In the meantime, deploys can stop Nerve when they start, and then re-start it at the end.

SkyDNS and SmartStack are both open source tools. SkyDNS with 1.97K GitHub stars and 301 forks on GitHub appears to be more popular than SmartStack with 228 GitHub stars and 41 GitHub forks.