ADR: Geth node (upstream/LES/ULC) (#4243)

doc/decisions/0003-geth-node.md

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+# 0003. Geth node for Beta
+
+| Date | Tags |
+|---|---|
+| 2018-05-14 | architecture, p2p, scope   |
+
+
+## Status
+
+proposed
+
+## Context
+
+On the path to releasing a usable beta we've faced a variety of performance
+issues:
+
+- https://github.com/status-im/ideas/issues/55
+- https://ideas.status.im/ideas/071-low-traffic
+- https://ideas.status.im/ideas/076-smooth-ui
+- https://ideas.status.im/ideas/083-energy-efficient
+
+Some of these performance issues are related to the use of LES, especially on
+Mainnet. Examples of problems include: slow/hot sync, disk filling up, bandwidth
+usage, etc. This can partly be remedied by the use of CHT to speed up sync
+(https://github.com/status-im/status-go/wiki/Updating-CHT-BloomTrie).
+
+In order to simplify the problem, we decided earlier this year to not spend too
+much time looking into performance improvements related to LES, instead focusing
+our efforts on improving the performance on Whisper and in client-side code.
+
+This also means we don't have a full picture of to what extent LES is a
+performance bottleneck for the Status app. It is possible proper use of CHT,
+slowing sync down, vary load depending on if you are on WiFi or not, etc, can
+solve these problems. However, the consensus right now is that ULC is the more
+promising route to take.
+
+However, since ULC isn't ready yet, this means we are relying on Infura. This
+is a bad idea from a decentralization and security point of view. This can be
+partly remedied by allowing the user to run an upstream node. It is still a bad
+trust model, relying on third-party Ethereum nodes, and we want to get away
+from this as soon as possible.
+
+With ULC it is possible to connect to more than one node, which increases
+decentralization and security.
+
+## Decision
+
+1. Rely on upstream nodes for beta. For the closed beta scheduled to be releases
+Q2 we will provide two ways of accessing the Ethereum network:
+
+- Upstream RPC with Infura (default)
+- Custom upstream node (https://github.com/status-im/status-react/issues/3994)
+
+From a decentralization point of view we need the latter before we can release
+the beta.
+
+2. ULC MVP. Additionally, as soon as beta is released, assess and start to
+   introduce ULC as an experimental non-default mode in the app.
+   
+By doing this we also support the network, since it is still a very new
+protocol. ULC requires trusted peers to operate, and right now trust is
+established by config (list of trusted peers).
+
+Initially we could hardcode these nodes, with option to add your own. Later on
+we can have some form of distributed directory with a rating system. This also
+likely requires merging ULC upstream, so we aren't the only ones running trusted
+nodes.
+
+3. LES track (optional). If we still have resources and there's interest,
+optionally run a parallel track to clean up LES usage (update CHT, cluster) and
+understand exact performance impact and viablity of running LES on
+resource-constrained devices.
+
+These three decisions balances the following trade-offs:
+
+- get a usable beta released as soon as possible
+- provide users with options to get minimal amount of decentralization
+- pave the way for trustless usage by default (ULC/LES node)
+
+## Consequences
+
+Most of this is captured above.
+
+- 1. Make sure custom upstream RPC is in beta and works
+- 2. Disable LES from beta release as it currently doesn't work reliably
+- 3. Continue work on https://github.com/status-im/ideas/pull/254/files, consider
+  adding more resources to get it into MVP state as soon as possible