Strategy to assign machine IDs based on the current node's network identifiers (hostname, FQDN, IP addresses, or OTP node name), matched against a fixed list of all possible nodes.
Each entry in node_list receives a stable zero-based index as its machine ID. No external
coordinator is required — IDs are determined locally — but every node must be configured with
the same list. The list is treated as a set: insertion order does not affect which ID is
assigned.
Configure the strategy when starting NoNoncense.MachineId:
children = [
{NoNoncense.MachineId,
strategy: NoNoncense.MachineId.Strategy.HostIdentifiers,
strategy_opts: [node_list: [:"myapp@10.0.0.1", :"myapp@10.0.0.2"]],
instances: [[base_key: System.fetch_env!("BASE_KEY")]]}
]The default ConflictGuard detects duplicate IDs among connected Erlang nodes.
Options
:node_list(required) - identifiers (IP addresses, OTP node names, hostnames, or FQDNs) for every node in the cluster; must be identical on every node and must not contain identifiers shared across nodes (e.g. do not include:"nonode@nohost")
Use the same node list everywhere
Your node_list must be the same for every node or the generated machine IDs will not be unique.
Summary
Functions
Get a list of all identifiers of the current node. You can use one or more of these values to populate your node list.
Determine the current node's machine ID.
Types
@type opt() :: {:node_list, host_identifiers()}
Functions
@spec host_identifiers() :: host_identifiers()
Get a list of all identifiers of the current node. You can use one or more of these values to populate your node list.
Examples / doctests
iex> host_identifiers()
[:nonode@nohost, "host.mydomain.com", "10.11.12.13", "myhost", "fe80::1234::abcd"]@spec id!([opt()]) :: non_neg_integer()
Determine the current node's machine ID.
Examples / doctests
# provide a list of possible node identifiers
iex> node_list = [:a, :b, :nonode@nohost, "1.1.1.1"]
iex> id!(node_list: node_list)
2
# raises when the machine ID could not be determined from the node list
iex> node_list = ["1.1.1.1"]
iex> id!(node_list: node_list)
** (RuntimeError) machine ID could not be determined