When configuring a cluster, you want tot keep managing the server as simple as possible. Theoretically, the results given by any node in the cluster should be equal as you want the cluster to be transparent to the end-user. Part of doing this, is having the same data available on every node of the cluster when it’s active. One way to do this, is using a central file-share, for example over NFS but this also has disadvantages. Another way is to have a distributed file system that stays on the nodes itself. DRBD is one of them. This post explains how to integrate DRBD in a cluster with Corosync and Pacemaker.
Besides using NAT for accessing the internet with multiple machines using a single IP address, there are many other uses of NAT. One of them is to forward all traffic that is sent to a certain TCP port to another host. In practice, this technique can be used to test a service on a new host without adjusting anything on the client. The users or the clients do not need to be pointed to a new machine in order to test it. When the test would be unsuccessful, removing the NAT-rule is all it takes to switch back.
In the not so far past, I spent a lot of my time working with and configuring z/OS or MVS mainframes. Over time, I managed to collect a serious collection of useful MVS-commands. Most of these commands can just be found in the forests of IBM documentation but the keyword in my previous sentence is “useful”. I found it, even as a person who was working for years in z/OS environments always difficult to get the right command for a certain action. The lack of examples and over-theoretical explanations made it, at least for me, not very accessible.