- All peers discovered are emitted via the
peer:discoveryevent so applications can take any desired action - To ensure reasonable resource usage, discovered peers are not connected to automatically
- Applications should lisen for the
peer:connectevent if they wish to take a specific action when new connections are established - Libp2p functions best with a good number of network connections to a diverse set of peers. When the number of connected peers a node has falls under the ConnectionManager
minConnectionssetting, randomly selected peers from the peer store will be dialed until the node's number of connections rises above this number. - Applications can disable this behaviour by setting the
connectionManager.minConnectionsconfig property to0, but they will have to manage increasing the current number of connections themselves.
The scenarios listed below detail what actions libp2p will take when peers are discovered.
In any scenario, if a peer is discovered it is added to the peer store. This ensures that we know about the peer in the event that it becomes known as a provider for something we need, even if we don't have a direct connection to it at the time.
The node is new and needs to join the network. It currently has 0 peers.
Connect to more peers.
- Configured Ambient Discovery mechanisms may begin discovering peers
- The node will run a network query for it's own PeerId which will discover nodes that are KAD-close to it's own ID
- It will search the peer store and dial and peers previously tagged with
KEEP_ALIVE
The node is connected to other nodes. The current number of connections is fewer than the desired amount, expressed as the ConnectionManager minConnections setting, also referred to as the low watermark.
Connect to more peers.
- The node will select nodes from the peer store and dial them until the number of connections is above the low watermark
- Configured Ambient Discovery mechanisms may continue discovering peers
- The node will periodically run a network query for it's own PeerId which will discover nodes that are KAD-close to it's own ID
The number of peers the node has is above the low watermark and below the high watermark.
None. As other peers discover us, they may connect to us based on their current scenario.
For example, a long running node with adequate peers is on an MDNS network. A new peer joins the network and both become aware of each other. The new peer should be the peer that dials, as it has too few peers. The existing node has no reason to dial the new peer, but should keep a record of it in case it later becomes an important node due to its contents/capabilities.
Avoiding dials above the minConnections also allows for a pool of connections to be reserved for application specific actions, such as connecting to a specific content provider via a DHT query to find that content (ipfs-bitswap).
The node has more connections than it wants. The current number of connections is greater than the desired amount, expressed as the ConnectionManager maxOutgoingConnections setting, also referred to as the high watermark.
The ConnectionManager will automatically prune connections.
It ranks peers based on their tags and the duration of the connection. Tags with lower values and shorter lived connections are pruned first.
Means of which a libp2p node discovers other peers.
Through active use of the libp2p network, a node may discovery peers.
- Content/Peer routing (DHT, delegated, etc) provider and peer queries
- DHT queries - network traversal can pass through previously unknown nodes
Leveraging known addresses, or network discovery mechanisms, a node may discover peers outside of the bounds of the libp2p network.
- Bootstrap - a list of known peers
- MDNS - local network discovery
- Proximity based (bluetooth, sound, etc) - not currently implemented