Don't persist gossip encryption keys

[grantr]

A common security recommendation is to store credentials and secret keys on a ramdisk so that they go away if the host is rebooted and are never persisted.

Would it be possible to (optionally) store the keyring state only in memory? With this enabled, the agent would always use the provided key on start, trusting that it will be the current key, then get the rest of the keyring from other nodes.

An external system would be responsible for ensuring that each node has the correct key to use on start.

One workaround for not having this feature is putting the entire serf directory on a ramdisk. Would that cause any issues? Is there state in the serf directory that needs to be persisted across reboots?

[ryanuber]

It is possible that we could support an option for not persisting the keyring to a file. It is already kept in-memory, we just make a call to a serializer method to persist it when it changes. I could see that being useful optional behavior. Marking as an enhancement.

The serf directory also contains the serf snapshots, which are used to store cluster state like alive nodes. This is used to perform automatic re-joins among other things. Nuking the serf directory isn't something we thought about/intended users to do, but you could definitely give it a shot.

[grantr]

Thanks @ryanuber!