One of requirements of Managed multi-nodes cluster is private network. Could someone explain it in detail for me? Does it need vlan or a dedicated trunk? Do those three Cassandra database need to be installed upon a cluster of three Linux servers like Oracle grid/rack databases?
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Someone may be able to answer this better but I have never seen it matter what the specifics of the private network need to be. I think this just means that they shouldn't need to communicate over a public network, they don't need their own dedicated private network or anything, just need to have the required ports opened:
Additionally Cassandra is not something you set up separately or manually, it is installed on your node as part of the node installer. You just need to make sure that your nodes meet the hardware/software requirements.
The whole process is supposed to be as simple as possible so if you don't see something specified in the documentation it probably either is handled for you during install or doesn't matter.
To add on to James' answer: as he said it is all about connectivity of course. So the cluster nodes need to be able to communicate on the ports outlined in the link.
However, it is important to note that the nodes will share quite an amount of data between them, as our Cassandra and ElasticSearch nodes need to replicate their data across the nodes. A general rule of thumb is that 80% of the traffic going into 1 particular node, will be sent to the other nodes. So if you have 10 Mbit of traffic going into node 1, 4Mbit will be sent to nodes 2 and 3 (in a 3 node cluster).
For that reason we suggest the same network segment in order to not run into bandwidth constraints.
The Dynatrace Managed installer creates all the required iptables configuration so that all nodes - and only the nodes - can communicate on the required ports.
Hope this helps.