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57/STATUS-Simple-Scaling

Abstract​

This document describes how to scale 56/STATUS-COMMUNITIES as well as 55/STATUS-1TO1-CHAT using Waku v2 protocol and components. It also adds a few new aspects, where more sophisticated components are not yet researched and evaluated.

> Note: (Parts of) this RFC will be deprecated in the future as we continue research to scale specific components in a way that aligns better with our principles of decentralization and protecting anonymity. This document informs about scaling at the current stage of research and shows it is practically possible. Practical feasibility is also a core goal for us. We believe in incremental improvement, i.e. having a working decentralized scaling solution with trade-offs is better than a fully centralized solution.

Background and Motivation​

56/STATUS-COMMUNITIES as well as 55/STATUS-1TO1-CHAT use Waku v2 protocols. Both use Waku content topics (see 23/WAKU2-TOPICS) for content based filtering.

Waku v2 currently has scaling limitations in two dimensions:

1) Messages that are part of a specific content topic have to be disseminated in a single mesh network (i.e. pubsub topic). This limits scaling the number of messages disseminated in a specific content topic, and by extension, the number of active nodes that are part of this content topic.

2) Scaling a large set of content topics requires distributing these over several mesh networks (which this document refers to as pubsub topic shards).

This document focuses on the second scaling dimension. With the scaling solutions discussed in this document, each content topics can have a large set of active users, but still has to fit in a single pubsub mesh.

> Note: While it is possible to use the same content topic name on several shards, each node that is interested in this content topic has to be subscribed to all respective shards, which does not scale. Splitting content topics in a more sophisticated and efficient way will be part of a future document.

Relay Shards​

Sharding the 11/WAKU2-RELAY network is an integral part of scaling the Status app.

51/WAKU2-RELAY-SHARDING specifies shards clusters, which are sets of 1024 shards (separate pubsub mesh networks). Content topics specified by application protocols can be distributed over these shards. The Status app protocols are assigned to shard cluster 16, as defined in WAKU2-RELAY-STATIC-SHARD-ALLOC.

WAKU2-RELAY-SHARDING specifies three sharding methods. This document uses static sharding, which leaves the distribution of content topics to application protocols, but takes care of shard discovery.

The 1024 shards within the main Status shard cluster are allocated as follows.

Shard Allocation​

shard indexusage
0 - 15reserved
16 - 127specific (large) communities
128 - 767communities
768 - 8951:1 chat
896 - 1023media and control msgs

Shard indices are mapped to pubsub topic names as follows (specified in WAKU2-RELAY-SHARDING).

/waku/2/rs/<cluster_id>/<shard_number>

an example for the shard with index 18 in the Status shard cluster:

/waku/2/rs/16/18

In other words, the mesh network with the pubsub topic name /waku/2/rs/16/18 carries messages associated with shard 18 in the Status shard cluster.

Implementation Suggestion​

The Waku implementation should offer an interface that allows Status nodes to subscribe to Status specific content topics like

subscribe("/status/xyz", 16, 18)

The shard cluster index 16 can be kept in the Status app configuration, so that Status nodes can simply use

subscribe("/status/xyz", 18)

which means: connect to the "status/xyz" content topic on shard 18 within the Status shard cluster.

Status Communities​

In order to associate a community with a shard, the community description protobuf is extended by the field uint16 relay_shard_index = 15:


syntax = "proto3";

message CommunityDescription {
  // The Lamport timestamp of the message
  uint64 clock = 1;
  // A mapping of members in the community to their roles
  map<string,CommunityMember> members = 2;
  // The permissions of the Community
  CommunityPermissions permissions = 3;
  // The metadata of the Community
  ChatIdentity identity = 5;
  // A mapping of chats to their details
  map<string,CommunityChat> chats = 6;
  // A list of banned members
  repeated string ban_list = 7;
  // A mapping of categories to their details
  map<string,CommunityCategory> categories = 8;
  // The admin settings of the Community
  CommunityAdminSettings admin_settings = 10;
  // If the community is encrypted
  bool encrypted = 13;
  // The list of tags
  repeated string tags = 14;
  // index of the community's shard within the Status shard cluster
  uint16 relay_shard_index = 15
}

> Note: Currently, Status app has allocated shared cluster 16 in 52/WAKU2-RELAY-STATIC-SHARD-ALLOC. Status app could allocate more shard clusters, for instance to establish a test net. We could add the shard cluster index to the community description as well. The recommendation for now is to keep it as a configuration option of the Status app.

> Note: Once this RFC moves forward, the new community description protobuf fields should be mentioned in 56/STATUS-COMMUNITIES.

Status communities can be mapped to shards in two ways: static, and owner-based.

Static Mapping​

With static mapping, communities are assigned a specific shard index within the Status shard cluster. This mapping is similar in nature to the shard cluster allocation in WAKU2-RELAY-STATIC-SHARD-ALLOC. Shard indices allocated in that way are in the range 16 - 127. The Status CC community uses index 16 (not to confuse with shard cluster index 16, which is the Status shard cluster).

Owner Mapping​

> Note: This way of mapping will be specified post-MVP.

Community owners can choose to map their communities to any shard within the index range 128 - 767.

1:1 Chat​

55/STATUS-1TO1-CHAT uses partitioned topics to map 1:1 chats to a set of 5000 content topics. This document extends this mapping to 8192 content topics that are, in turn, mapped to 128 shards in the index range of 768 - 895.

contentPartitionsNum = 8192
contentPartition = mod(publicKey, contentPartitionsNum)
partitionContentTopic = "contact-discovery-" + contentPartition

partitionContentTopic = keccak256(partitionContentTopic)

shardNum = 128
shardIndex = 768 + mod(publicKey, shardNum)

Infrastructure Nodes​

As described in 30/ADAPTIVE-NODES, Waku supports a continuum of node types with respect to available resources. Infrastructure nodes are powerful nodes that have a high bandwidth connection and a high up-time.

This document, which informs about simple ways of scaling Status over Waku, assumes the presence of a set of such infrastructure nodes in each shard. Infrastructure nodes are especially important for providing connectivity in the roll-out phase.

Infrastructure nodes are not limited to Status fleets, or nodes run by community owners. Anybody can run infrastructure nodes.

Statically-Mapped Communities​

Infrastructure nodes are provided by the community owner, or by members of the respective community.

Owner-Mapped Communities​

Infrastructure nodes are part of a subset of the shards in the range 128 - 767. Recommendations on choosing this subset will be added in a future version of this document.

Status fleet nodes make up a part of these infrastructure nodes.

1:1 chat​

Infrastructure nodes are part of a subset of the shards in the range 768 - 985 (similar to owner-mapped communities). Recommendations on choosing this subset will be added in a future version of this document.

Desktop clients can choose to only use filter and lightpush.

> Note: Discussion: I'd suggest to set this as the default for the MVP. The load on infrastructure nodes would not be higher, because they have to receive and relay each message anyways. This comes as a trade-off to anonymity and decentralization, but can significantly improve scaling. We still have k-anonymity because several chat pairs are mapped into one content topic. We could improve on this in the future, and research the applicability of PIR (private information retrieval) techniques in the future.

Infrastructure Shards​

Waku messages are typically relayed in larger mesh networks comprised of nodes with varying resource profiles (see 30/ADAPTIVE-NODES. To maximise scaling, relaying of specific message types can be dedicated to shards where only infrastructure nodes with very strong resource profiles relay messages. This comes as a trade-off to decentralization.

Control Message Shards​

To get the maximum scaling for select large communities for the Status scaling MVP, specific control messages that cause significant load (at a high user number) SHOULD be moved to a separate control message shard. These control messages comprise:

  • community description
  • membership update
  • backup
  • community request to join response
  • sync profile picture

The relay functionality of control messages shards SHOULD be provided by infrastructure nodes. Desktop clients should use light protocols as the default for control message shards. Strong Desktop clients MAY opt in to support the relay network.

Each large community (in the index range of 16 - 127) can get its dedicated control message shard (in the index range 896 - 1023) if deemed necessary. The Status CC community uses shard 896 as its control message shard. This comes with trade-offs to decentralization and anonymity (see Security Considerations section).

Media Shards​

Similar to control messages, media-heavy communities should use separate media shards (in the index range 896 - 1023) for disseminating messages with large media data. The Status CC community uses shard 897 as its media shard.

Infrastructure-focused Community​

Large communities MAY choose to mainly rely on infrastructure nodes for all message transfers (not limited to control, and media messages). Desktop clients of such communities should use light protocols as the default. Strong Desktop clients MAY opt in to support the relay network.

> Note: This is not planned for the MVP.

Light Protocols​

Light protocols may be used to save bandwidth, at the (global) cost of not contributing to the network. Using light protocols is RECOMMENDED for resource restricted nodes, e.g. browsers, and devices that (temporarily) have a low bandwidth connection or a connection with usage-based billing.

Light protocols comprise

Waku Archive​

Archive nodes are Waku nodes that offer the Waku archive service via the Waku store protocol (13/WAKU2-STORE). They are part of a set of shards and store all messages disseminated in these shards. Nodes can request history messages via the 13/WAKU2-STORE.

The store service is not limited to a Status fleet. Anybody can run a Waku Archive node in the Status shards.

> Note: There is no specification for discovering archive nodes associated with specific shards yet. Nodes expect archive nodes to store all messages, regardless of shard association.

The recommendation for the allocation of archive nodes to shards is similar to the allocation of infrastructure nodes to shards described above. In fact, the archive service can be offered by infrastructure nodes.

Discovery​

Shard discovery is covered by WAKU2-RELAY-SHARDING. This allows the Status app to abstract from the discovery process and simply address shards by their index.

Libp2p Rendezvous and Circuit-Relay​

To make nodes behind restrictive NATs discoverable, this document suggests using libp2p rendezvous. Nodes can check whether they are behind a restrictive NAT using the libp2p AutoNAT protocol.

> Note: The following will move into WAKU2-RELAY-SHARDING, or 33/WAKU2-DISCV5: Nodes behind restrictive NATs SHOULD not announce their publicly unreachable address via 33/WAKU2-DISCV5 discovery.

It is RECOMMENDED that nodes that are part of the relay network also act as rendezvous points. This includes accepting register queries from peers, as well as answering rendezvous discover queries. Nodes MAY opt-out of the rendezvous functionality.

To allow nodes to initiate connections to peers behind restrictive NATs (after discovery via rendezvous), it is RECOMMENDED that nodes that are part of the Waku relay network also offer libp2p circuit relay functionality.

To minimize the load on circuit-relay nodes, nodes SHOULD

1) make use of the limiting functionality offered by the libp2p circuit relay protocols, and 2) use DCUtR to upgrade to a direct connection.

Nodes that do not announce themselves at all and only plan to use light protocols, MAY use rendezvous discovery instead of or along-side WAKU2-PEER-EXCHANGE. For these nodes, rendezvous and WAKU2-PEER-EXCHANGE offer the same functionality, but return node sets sampled in different ways. Using both can help increasing connectivity.

Nodes that are not behind restrictive NATs MAY register at rendezvous points, too; this helps increasing discoverability, and by extension connectivity. Such nodes SHOULD, however, not register at circuit relays.

Announcing Shard Participation​

Registering a namespace via lib-p2p rendezvous is done via a register query:

REGISTER{my-app, {QmA, AddrA}}

The app name, my-app contains the encoding of a single shard in string form:

"rs/"| to_string(<2-byte shard cluster index>) | "/" | to_string(<2-byte shard index>)

The string conversion SHOULD remove leading zeros.

> Note: Since the ns field is of type string, a more efficient byte encoding is not utilized.

Registering shard 2 in the Status shard cluster (with shard cluster index 16, see WAKU2-RELAY-STATIC-SHARD-ALLOC, the register query would look like

REGISTER{"rs/16/2", {QmA, AddrA}}

Participation in further shards is registered with further queries; one register query per shard.

A discovery query for nodes that are part of this shard would look like

DISCOVER{ns: "rs/16/2"}

DoS Protection​

Hereunder we describe the "opt-in message signing for DoS prevention" solution, designed ad hoc for Status MVP.

Since publishing messages to pubsub topics has no limits, anyone can publish messages at a very high rate and DoS the network. This would elevate the bandwidth consumption of all nodes subscribed to said pubsub topic, making it prohibitive (in terms of bandwidth) to be subscribed to it. In order to scale, we need some mechanism to prevent this from happening, otherwise all scaling efforts will be in vain. Since RLN is not ready yet, hereunder we describe a simpler approach designed ad hoc for Status use case, feasible to implement for the MVP and that validates some of the ideas that will evolve to solutions such as RLN.

With this approach, certain pubsub topics can be optionally configured to only accept messages signed with a given key, that only trusted entities know. This key can be pre-shared among a set of participants, that are trusted to make fair usage of the network, publishing messages at a reasonable rate/size. Note that this key can be shared/reused among multiple participants, and only one key is whitelisted per pubsub topic. This is an opt-in solution that operators can choose to deploy in their shards (i.e. pubsub topics), but it's not enforced in the default one. Operators can freely choose how they want to generate, and distribute the public keys. It's also their responsibility to handle the private key, sharing it with only trusted parties and keeping proper custody of it.

The following concepts are introduced:

  • private-key-topic: A private key of 32 bytes, that allows the holder to sign messages and it's mapped to a protected-pubsub-topic.
  • app-message-hash: Application WakuMessage hash, calculated as sha256(concat(pubsubTopic, payload, contentTopic)) with all elements in bytes.
  • message-signature: ECDSA signature of application-message-hash using a given private-key-topic, 64 bytes.
  • public-key-topic: The equivalent public key of private-key-topic.
  • protected-pubsub-topic: Pubsub topic that only accepts messages that were signed with private-key-topic, where verify(message-signature, app-message-hash, public-key-topic) is only correct if the message-signature was produced by private-key-topic. See ECDSA signature verification algorithm.

This solution introduces two roles:

  • Publisher: A node that knows the private-key-topic associated to public-key-topic, that can publish messages with a valid message-signature that are accepted and relayed by the nodes implementing this feature.
  • Relayer: A node that knows the public-key-topic, which can be used to verify if the messages were signed with the equivalent private-key-topic. It allows distinguishing valid from invalid messages which protect the node against DoS attacks, assuming that the users of the key send messages of a reasonable size and rate. Note that a node can validate messages and relay them or not without knowing the private key.

Design requirements (publisher)​

A publisher that wants to send messages that are relayed in the network for a given protected-pubsub-topic shall:

  • be able to sign messages with the private-key-topic configured for that topic, producing a ECDSA signature of 64 bytes using deterministic signing complying with RFC 6979.
  • include the signature of the app-message-hash (message-signature) that wishes to send in the WakuMessage meta field.

The app-message-hash of the message shall be calculated as the sha256 hash of the following fields of the message:

sha256(concat(pubsubTopic, payload, contentTopic, timestamp, ephemeral))

Where fields are serialized into bytes using little-endian. Note that ephemeral is a boolean that is serialized to 0 if false and 1 if true.

Design requirements (relay)​

Requirements for the relay are listed below:

  • A valid protected-pubsub-topic shall be configured with a public-key-topic, (derived from a private-key-topic). Note that the relay does not need to know the private key. For simplicity, there is just one key per topic. Since this approach has clear privacy implications, this configuration is not part of the waku protocol, but of the application.

Requirements on the gossipsub validator:

  • Relay nodes should use the existing gossipsub validators that allow to Accept or Reject messages, according to the following criteria:
  • If timestamp is not set (equals to 0) then Reject the message.
  • If the timestamp is abs(current_timestamp-timestamp) > MessageWindowInSec then Reject the message.
  • If meta is empty, Reject the message.
  • If meta exists but its size is different than 64 bytes, Reject the message.
  • If meta does not successfully verifies according to the ECDSA signature verification algorithm using public-key-topic and app-message-hash, then Reject the message.
  • If and only if all above conditions are met then Accept the message.

Other requirements:

  • The node shall keep metrics on the messages validation output, Accept or Reject.
  • (Optional). To further strengthen DoS protection, gossipsub scoring can be used to trigger disconnections from peers sending multiple invalid messages. See P4 penalty. This protects each peer from DoS, since this score is used to trigger disconnections from nodes attempting to DoS them.

Required changes​

This solution is designed to be backward compatible so that nodes validating messages can coexist in the same topic with other nodes that don't perform validation. But note that only nodes that perform message validation will be protected against DoS. Nodes wishing to opt-in this DoS protection feature shall:

  • Generate a private-key-topic and distribute it to a curated list of users, that are trusted to send messages at a reasonable rate.
  • Redeploy the nodes, adding a new configuration where a protected-pubsub-topic is configured with a public-key-topic, used to verify the messages being relayed.

Test vectors​

Relay nodes complying with this specification shall accept the following message in the configured pubsub topic.

Given the following key pair:

private-key-topic = 5526a8990317c9b7b58d07843d270f9cd1d9aaee129294c1c478abf7261dd9e6
public-key-topic = 049c5fac802da41e07e6cdf51c3b9a6351ad5e65921527f2df5b7d59fd9b56ab02bab736cdcfc37f25095e78127500da371947217a8cd5186ab890ea866211c3f6

And the following message to send:

protected-pubsub-topic = pubsub-topic
contentTopic = content-topic
payload = 1A12E077D0E89F9CAC11FBBB6A676C86120B5AD3E248B1F180E98F15EE43D2DFCF62F00C92737B2FF6F59B3ABA02773314B991C41DC19ADB0AD8C17C8E26757B
timestamp = 1683208172339052800
ephemeral = true

The message hash and meta (aka signature) are calculated as follows.

app-message-hash = 662F8C20A335F170BD60ABC1F02AD66F0C6A6EE285DA2A53C95259E7937C0AE9
message.meta = 127FA211B2514F0E974A055392946DC1A14052182A6ABEFB8A6CD7C51DA1BF2E40595D28EF1A9488797C297EED3AAC45430005FB3A7F037BDD9FC4BD99F59E63

Using message.meta, the relay node shall calculate the app-message-hash of the received message using public-key-topic, and with the values above, the signature should be verified, making the node Accept the message and relaying it to other nodes in the network.

Owner-Mapped Communities​

Basic idea: Tokenized load.

1:1 Chat​

An idea we plan to explore in the future: Map 1:1 chats to community shards, if both A and B are part of the respective community. This increases k-anonymity and benefits from community DoS protection. It could be rate-limited with RLN.

Security/Privacy Considerations​

This document makes several trade-offs to privacy and anonymity. Todo: elaborate. See WAKU2-ADVERSARIAL-MODELS for information on Waku Anonymity.

Copyright and related rights waived via CC0.

References​

Informative​