Discovery protocol is essential for long-term scaling of the Status app. It will improve security of our cluster and reliability of the app and prepare it for the beta launch.
Discovery protocol will allow us to dynamically change the number of server peers in our cluster and also distribute the peers among various providers and countries without rebuilding the app itself, hence improving security and reliability.
The biggest challenge may be increased CPU and network usage. This needs to be carefully measured and we may end up with proposing some protocol changes.
#### Q: CPU/network increase usage. How does it change in absolute and relative values? How to reproduce the measurement?
**A:** TBD
#### Q: Can we turn on and off discovery protocol when the node is running?
**A:** Yes. First of all, we can tell how often the Discovery V5 should search for new peers with a given topic. Also, as we implemented Discovery V5 as a peer pool, we managed the list of peers. If the number of peers found for all topics is equal or exceed the upper limit, we can disable Discover V5 completely.
#### Q: Can Discovery V5 protocol carry more information than protocol name and version? How can we distinguish Light Whisper nodes or Whisper nodes with MailServer capability? Notice that revealing this information (like Light Whisper node) may increase a chance to reveal the peer identity. The fact that we don’t want mobile phones to be each other peers raises this question.
**A:** Topic can be an arbitrary `key=value` pair. The rest will be answer later...
#### Q: How to make sure that connecting to the cluster will be fast? When the app goes to the background, does it take significantly more time to find peers? Do we need to use cache? From the cluster perspective, how to autoscale cluster so that its free capacity is always high?
**A**: We need a cache to quickly provide the list of recently used peers. If the app fails to connect to them, it will use Discovery V5 in fast mode (checking for new peers more often).
To use Discovery V5, we need to set up bootnodes, however, they can use the existing server nodes, provided that they advertise Discovery V5 topics.
*Provide answer for cluster autoscaling.*
#### Q: How to make sure that there are always at least `N` peers with given capabilities? For instance, we always want to have at least `K` Whisper, `L` MailServer and `M` LES peers connected.
**A:** This is implemented in [`github.com/status-im/status-go/geth/peers`](https://github.com/status-im/status-go/tree/develop/geth/peers) package. For each topic we are interested in, a lower and upper limits are provided. `PeerPool` and `TopicPool` take care of maintaining the number of peers within the limits.
1. Assess if DiscV5 is a viable protocol to replace static nodes.
1. If so, there is a list of issues that we should work on to further improve DiscV5 usage in the Status app and in the cluster (this may be realized as next iterations or a new swarm).
1. Connecting to the network for statusd/Status App via DiscV5 is successful in at least 99% of tries,
1. It's possible to discover minimal number of LES/2, Whisper and MailServer nodes via DiscV5 within 15 seconds without cache and in 5 seconds with cache,
1. Resources consumption (CPU and network ingress/egress) is not higher than 20% compared to static nodes.
