Difference between primary node type and seed node

Question

What is the difference between primary node types and seed nodes. My understanding is primary node types run Service Fabric system services, but not quite clear on seed nodes. Are certain system services only run by seed nodes? (I noticed for instance DNS service is running on all nodes after adding more nodes, but others like Cluster manager only running on seed nodes). Would scaling in a cluster with only primary node types cause any issues?

Answer 1

@Muriuki, Levi M

Welcome to Microsoft Q&A Platform, thanks for posting your query here.

Primary NodeType: Exactly one node type in SFRP tenant cluster is marked as primary. All system services and seed nodes are present in this node type.

Seed nodes are in accordance with the Cluster's Reliability Level. So if Cluster's reliability is Bronze, it will have 3 seed nodes in Primary Nodetype, if its Silver then 5 seed nodes in Primary Nodetype and so on. These are nodes that maintain the availability of the underlying cluster. Seed nodes help to ensure that the cluster stays up by establishing leases with other nodes and serving as tiebreakers during certain kinds of failures.

DNS Service is an optional service in Service Fabric and is one of the means for Service Communication. Reference https://learn.microsoft.com/en-us/azure/service-fabric/service-fabric-connect-and-communicate-with-services.

Refer more details on System Services here https://learn.microsoft.com/en-us/azure/service-fabric/service-fabric-technical-overview#system-services

Hope this helps.
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