In your opinion which of the two session persistance options is more resource intensive, and requires more CPU cycles ?
I am aware that the transparent session affinity requires deep packet inspection all the way to Layer 7 to be able to see the cookie and that IP-based persistence requires in-memory table structure to keep track of all connections.
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The layer 7 inspection will be fractionally more 'expensive', but the impact is probably negligible because Stingray always runs in a layer-7 mode (there's no fast-path L4 mode that gives great benchmarks but can't be used in real life).
On the other hand, the IP-based session persistent method carries the state sharing overhead - the internal session table is synchronized across the cluster.
For a complete understanding of the impact, you'll want to consider the other activities the traffic manager is performing (if you're already doing lots of rules and traffic modification, the impact of either will be negligible) and probably will need to benchmark the two to compare.
In reality, if your Stingray host server is less than 80% utilized, you'll probably not see any performance or utilization impact. And if it's that utlized, you ought to think of moving to a more capable server so that you have >50% overhead for large traffic spikes.
Thank you for the reply!
I would like to know how big (roughly) one entry in the state table is for earch connection ( I would imagine less than 50K ?), so I can calculate some estimates for say 1Mil connections, and how big the memroy structure will be. I ca see this becoming a problem if 10G of memory needs to be replicated between our nodes. Also, how long a session is cached in memory? Any suggestions on this will be highly appreciated!
The IP-session table is sized using the ip_cache_size parameter in the 'cache' section of the global settings. Each entry is approx 100 bytes in size.
You can instrument the behaviour of the cache on a running system using the various activity monitor counters for that cache, or via SNMP. The Monitoring and Debugging section of the article Feature Brief: Session Persistence in Stingray Traffic Manager describes this in more detail.