Remote.Peer

Exposes mechanisms for a program built on the Remote.Process framework to discover nodes on the current network. Programs can perform node discovery manually, or they can use Remote.Task, which does it automatically.

Documentation

type PeerInfo = Map String [NodeId]

Created by Remote.Peer.getPeers, this maps each role to a list of nodes that have that role. It can be examined directly or queried with findPeerByRole.

startDiscoveryService :: ProcessM ()

Starts the discovery process, allowing this node to respond to queries from getPeersDynamic. You don't want to call this yourself, as it's called for you in Remote.Init.remoteInit

getPeers :: ProcessM PeerInfo

Returns information about all nodes on the current network that this node knows about. This function combines dynamic and static mechanisms. See documentation on getPeersStatic and getPeersDynamic for more info. This function depends on the configuration values cfgKnownHosts and cfgPeerDiscoveryPort.

getPeersStatic :: ProcessM PeerInfo

Returns a PeerInfo, containing a list of known nodes ordered by role. This information is acquired by querying the local node registry on each of the hosts in the cfgKnownHosts entry in this node's config. Hostnames that don't respond are assumed to be down and nodes running on them won't be included in the results.

getPeersDynamic :: Int -> ProcessM PeerInfo

Returns a PeerInfo, containing a list of known nodes ordered by role. This information is acquired by sending out a UDP broadcast on the local network; active nodes running the discovery service should respond with their information. If nodes are running outside of the local network, or if UDP broadcasts are disabled by firewall configuration, this won't return useful information; in that case, use getPeersStatic. This function takes a parameter indicating how long in microseconds to wait for hosts to respond. A number like 50000 is usually good enough, unless your network is highly congested or with high latency.

findPeerByRole :: PeerInfo -> String -> [NodeId]

Given a PeerInfo returned by getPeersDynamic or getPeersStatic, give a list of nodes registered as a particular role. If no nodes of that role are found, the empty list is returned.