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c9491d7861
This is the first (maybe not last) step in cleaning up the bootstrap code around StartNode. Initializing a Raft group for the first time is awkward, since a configuration has to be pulled from thin air. The way this is solved today is unclean: The app is supposed to pass peers to StartNode(), we add configuration changes for them to the log, immediately pretend that they are applied, but actually leave them unapplied (to give the app a chance to observe them, though if the app did decide to not apply them things would really go off the rails), and then return control to the app. The app will then process the initial Readys and as a result the configuration will be persisted to disk; restarts of the node then use RestartNode which doesn't take any peers. The code that did this lived awkwardly in two places fairly deep down the callstack, though it was really only necessary in StartNode(). This commit refactors things to make this more obvious: only StartNode does this dance now. In particular, RawNode does not support this at all any more; it expects the app to set up its Storage correctly. Future work may provide helpers to make this "preseeding" of the Storage more user-friendly. It isn't entirely straightforward to do so since the Storage interface doesn't provide the right accessors for this purpose. Briefly speaking, we want to make sure that a non-bootstrapped node can never catch up via the log so that we can implicitly use one of the "skipped" log entries to represent the configuration change into the bootstrap configuration. This is an invasive change that affects all consumers of raft, and it is of lower urgency since the code (post this commit) already encapsulates the complexity sufficiently.