ARD: Discovery protocol

Signed-off-by: Julien Eluard <julien.eluard@gmail.com>

doc/decisions/0005-discovery-protocol.md

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+# 0005. Use Discovery v5 protocol
+
+| Date | Tags |
+|---|---|
+| 2018-05-14 | architecture, p2p, ethereum |
+
+
+## Status
+
+proposed
+
+## Context
+
+Currently peers for messaging are hardcoded in the app. This means we can't
+easily scale, as some of these nodes might fill up when we have more than N
+active users.
+
+Discovery v5 protocol (https://ideas.status.im/ideas/092-disc-v5-research,
+https://github.com/fjl/p2p-drafts/blob/master/discv5-eip.md) allow us to
+discover new peers from the app and scale server peers in our cluster
+independently. This is vital for high availability/reliability and security.
+
+## Decision
+
+- Use and enable Discovery v5 for all networks
+- Do this before beta is released
+
+This means we have capacity to achieve 5000+ DAU / 500 concurrent connection. It
+seems unlikely we can do so with reliable messaging in the current setup.
+
+Trade-off for this is:
+- Uncertainty in introducing a new protocol leading to possible delays
+- Possible increase in CPU/Network (we can disable protocol once peers are found though)
+
+## Consequences
+
+- This is a top priority for P2P team, lead by @dshulyak and assisted by @adambabik and @jacob
+- We need this battle tested to get it into app as soon as possible
+- Chat, mobile team and QA team should be aware of this protocol change