I'm interested in having corosync automatically accept members into the cluster without manual reconfiguration. Meaning that when I bring a new node online, I want to configure it for the existing nodes, and those nodes will automatically add the new node into their nodelist. >From a purely technical standpoint, this doesn't seem like it would be hard to do. The only 2 things you have to do to add a node are add the nodelist.node.X.nodeid and ring0_addr to cmap. When the new node comes up, it starts sending out messages to the existing nodes. The ring0_addr can be discovered from the source address, and the nodeid is in the message.
Going even further, when using the allow_downscale and last_man_standing features, we can automatically remove nodes from the cluster when they disappear. With last_man_standing, the quorum expected votes is automatically adjusted when a node is lost, so it makes no difference whether the node is offline, or removed. Then with the auto-join functionality, it'll automatically be added back in when it re-establishes communication. It might then even be possible to write the cmap data out to a file when a node joins or leaves. This way if corosync restarts, and the corosync.conf hasn't been updated, the nodelist can be read from this save. If the save is out of date, and some nodes are unreachable, they would simply be removed, and added when they join. This wouldn't even have to be a part of corosync. Could have some external utility watch the cmap values, and take care of setting them when corosync is launched. Ultimately this allows us to have a large scale dynamically sized cluster without having to edit the config of every node each time a node joins or leaves. This really doesn't sound like it would be hard to do. I might even be willing to attempt implementing it myself if this sounds like something that would be acceptable to merge into the code base. Thoughts? -Patrick
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