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Topology configuration

The topology is a .yaml file specified using the --topology command line flag. When no .yaml file is specified the node is considered to be a behind-NAT edge node with a hardcoded set of default domain names to discover relays (see “Behind-NAT Nodes”, below).

SIGHUP can be sent to an already running node to make it re-read the topology file. Only a few settings can be changed dynamically in this manner. For instance, while it is possible to add additional routes, it is not possible to change a node’s type dynamically. To change other settings the node needs to be restarted. Sending SIGHUP also causes the outbound queue to clear its failure statistics (see

Statically configured nodes (core or relay)

Statically configured nodes are provided with a full list of all nodes and their types. It looks something like this:

    type: core
    region: eu-central-1
    static-routes: [["node1"], ["node2"]]
    host: node0.local
    # default port
    type: core
    region: eu-west-1
    static-routes: [["node0"], ["node2"]]
    # default port
    type: relay
    region: eu-west-2
    static-routes: [["node0"], ["node1"]]
    # uses 'node2' as the hostname
    port: 3000
    kademlia: false

The idea is that all statically configured nodes in the cluster share this file, and are additionally told which node in this list they are (--node-id command line flag). The yaml file contains the following information for each node:

  • Its type (core or relay)
  • Its region
  • Its hostname (host, to be resolved through DNS) or its IP address (addr); if neither of these is used, the node’s name will be used as its hostname.
  • Its port number. This is optional; if not used, the default port number will be used (currently set at 3000, can be changed using --default-port).
  • It’s peers (explained in more detail below).
  • Whether or not to run Kademlia. This defaults to true for relay nodes and to false for core nodes.

The interpretation of the list of lists in the static-routes is as follows: when a message gets enqueued to a set of peers


then the message will be sent to four nodes: one chosen from [a1,a2,a3], one chosen from [b1,b2,b3], etc. (this choice is made based on heuristics that approximate how busy the destination is). These static routing tables should be carefully constructed to minimize network fragmentation.

Note that relay nodes register themselves with the Kademia network, but core nodes do not (see below for Kademlia configuration).

Behind-NAT wallet (edge) nodes

Behind NAT nodes are provided with a list of lists of domain names, which they use to discover relays. It looks something like

  relays: [[{"host": "domain1"},{"host": "domain2", "port": 1234}]]
  valency: 3   # optional
  fallbacks: 2 # optional

The interpretation of the list of lists here is as follows. If the list looks like


then the node will query DNS to resolve domain names a1 and a2 by default. This yields a set of IP addresses (possibly larger than 2, since a domain name can result in multiple IP addresses), which the edge node will try in turn. The alternative sets of domain names will be used only if one of the domain names in the first list could not be resolved. The relay node will be contacted on the port number specified in the yaml file, or on the default port otherwise (--default-port).

In order to support behind NAT nodes that for whatever reason cannot do DNS resolution, it is also possible to include relay nodes by IP address in this list, using addr instead of host; the structure remains otherwise the same:

  relays: [[{"addr": ""},{"addr": "", "port": 1234}]]

Peer-to-peer nodes

Peer-to-peer nodes are very similar to behind-NAT nodes; they are also considered edge nodes, but instead of using DNS to find relays, they use Kademlia. Their configuration looks something like

  variant: normal
  valency: 3
  fallbacks: 1

The valency and fallbacks parameters specify what kind of routing we should set up (in the static nodes example above, valency = 4 and fallbacks = 2 (TODO: verify that that is true).

Traditional mode

In traditional mode all nodes find each other using Kademlia, and moreover all nodes are considered core nodes. The configuration is similar to that of P2P nodes:

  variant: traditional
  valency: 3
  fallbacks: 1

Behind-NAT is not (explicitly) supported in traditional mode (though workarounds using SSH tunnelling or similar are of course possible).


The auxx uses a specialized topology, in which it is given a specific set of nodes to connect to. This is hardcoded in the auxx itself, there is no yaml format for this mode.

Kademlia configuration