tendermint/docs/architecture/adr-050-improved-trusted-peering.md

ADR 50: Improved Trusted Peering

Changelog

• 22-10-2019: Initial draft
• 05-11-2019: Modify maximum_dial_period to persistent_peers_max_dial_period

Context

When max_num_inbound_peers or max_num_outbound_peers of a node is reached, the node cannot spare more slots to any peer by inbound or outbound. Therefore, after a certain period of disconnection, any important peering can be lost indefinitely because all slots are consumed by other peers, and the node stops trying to dial the peer anymore.

This is happening because of two reasons, exponential backoff and absence of unconditional peering feature for trusted peers.

Decision

We would like to suggest solving this problem by introducing two parameters in config.toml, unconditional_peer_ids and persistent_peers_max_dial_period.

1. unconditional_peer_ids

A node operator inputs list of ids of peers which are allowed to be connected by both inbound or outbound regardless of max_num_inbound_peers or max_num_outbound_peers of user's node reached or not.

2. persistent_peers_max_dial_period

Terms between each dial to each persistent peer will not exceed persistent_peers_max_dial_period during exponential backoff. Therefore, dial_period = min(persistent_peers_max_dial_period, exponential_backoff_dial_period)

Alternative approach

Persistent_peers is only for outbound, therefore it is not enough to cover the full utility of unconditional_peer_ids. @creamers158(https://github.com/Creamers158) suggested putting id-only items into persistent_peers to be handled as unconditional_peer_ids, but it needs very complicated struct exception for different structure of items in persistent_peers. Therefore we decided to have unconditional_peer_ids to independently cover this use-case.

Status

Proposed

Consequences

Positive

A node operator can configure two new parameters in config.toml so that he/she can assure that tendermint will allow connections from/to peers in unconditional_peer_ids. Also he/she can assure that every persistent peer will be dialed at least once in every persistent_peers_max_dial_period term. It achieves more stable and persistent peering for trusted peers.

Negative

The new feature introduces two new parameters in config.toml which needs explanation for node operators.

Neutral

References

• two p2p feature enhancement proposal(https://github.com/tendermint/tendermint/issues/4053)