I have seen a few issues utilizing the default value of reserved.broker.max.id=1000 in existing clusters during upgrades. For many that started broker.ids at 0 and incremented by 1 this may not be an issue. However, others may have very different numbering schemes.
Given that we have the entire Integer range to work with, I propose we increase the default to a much larger value. This will help reduce upgrade issues and also help more clearly identify generated broker ids.
Would defaulting to 1,000,000,000 be to large? Perhaps 1,000,000 is enough.