-zookeeper as configuration persistence medium?
Patrick Braga-Henebry 2012-11-29, 00:52
We've been using ZooKeeper for service discovery for a couple months now and have been pretty happy.
A bit about our setup: our ZK ensemble comprises 3 nodes and is spread across data centers. Compared to other ZK instances it is likely very low-traffic: perhaps 200 writes/1000 reads/500 clients per day. So, small potatoes in terms of traffic.
Currently all nodes stored in our ZK are actively managed/populated by specific clients, such that we would be able to theoretically wipe ZooKeeper and clients would repopulate znodes appropriately.
I wanted to use the community as a sounding board here. Reading through the ZK literature I've found, I haven't seen this use case mentioned explicitly:
Now we are considering storing configuration data in ZooKeeper. Currently this configuration is stored on the filesystem and read once at startup of a component.
My gut reaction is storing this data in ZooKeeper—using ZK itself as the persistence medium—is a bad idea. Because it would be storing data that isn't present anywhere else: supposing a ZK crash, we would need to replay transaction logs to get the data back, rather than using our existing backup solutions.
I think a better solution would be to write a component which is responsible for persisting and managing updates to this configuration, and makes it available to interested clients via ZooKeeper. This would keep all znodes programmatically generated, which I think would lead to a cleaner node space. It would also help you avoid orphaned nodes, sitting around and not being accessed/cleaned up anymore. Eventually nobody would know what those orphaned nodes are there for or if anyone is relying on their presence.
Am I on the right track here? Are there ZK deployments out there being used in this way? In addition, is there a way to check the last time a znode was used? Or, a pattern which encourages not orphaning nodes in the first place?
Thanks in advance,
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