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System Configuration

System configuration is a set of parameters that determine the network access parameters of a node and behavior of the node while operating in the network.

The configuration is stored in the TOML format. A path to the configuration file should be specified on the node start up.

The configuration may be changed using the Configuration Updater service or by editing the configuration file.

Services may have their own configuration settings. On node initialization the configuration is passed to all services deployed in the blockchain. The configuration for a service is stored in the services_configs subtree of the overall configuration under a separate key equal to the name of the service.


The configuration settings of the anchoring service include the parameters of the RPC connection to a Bitcoin Core node as well as a Bitcoin address used for anchoring. These parameters are stored in the services_configs.btc_anchoring section of the overall configuration.

Configuration Parameters

System configuration contains 2 types of configuration parameters:

  • Global parameters must be identical for all full nodes in the network. The global parameters are saved in the blockchain when the genesis block is created
  • Local parameters may differ for each node

This categorization holds for both core and service parameters.


The following table shows all 4 possible parameter categories.

Scope Core Anchoring service
Global Validators’ public keys Anchoring address
Local Validator’s private key RPC params for Bitcoin Core


See sample configuration file for reference.

Global Parameters


The configuration used to create a genesis block.


List of validators’ public keys as hex strings. Each list element consists of two parts:

  • consensus_key
    Validator’s public key (hex) for use with consensus messages
  • service_key
    Validator’s public key (hex) for use with service transactions


Consensus algorithm parameters.

  • max_message_len
    Maximum message length (in bytes). This parameter determines the maximum size of both consensus messages and transactions. The default value of the parameter is 1 MB (1024 * 1024 bytes). The range of possible values for this parameter is between 1MB and 2^32 bytes.
  • max_propose_timeout
    Maximum propose timeout (in ms)
  • min_propose_timeout
    Minimum propose timeout (in ms)
  • peers_timeout
    Peers exchange timeout (in ms)
  • propose_timeout_threshold
    Amount of transactions in the pool to start using min_propose_timeout
  • first_round_timeout
    Timeout interval (ms) of the first round at each height. The default value is 3000 ms. This parameter is used to estimate timeouts for further consensus rounds. See specification of the consensus algorithm for more details
  • status_timeout
    Timeout interval (ms) for sending a Status message
  • txs_block_limit
    Maximum number of transactions per block

Local Parameters

  • external_address
    The node address broadcasted to other peers using Connect messages
  • listen_address
    Listen address of the current node
  • peers
    List of full node addresses
  • consensus_public_key
    Node’s public key (hex) for use with consensus messages
  • consensus_secret_key
    Node’s private key (hex) for signing consensus messages
  • service_public_key
    Node’s public key (hex) for use with service transactions
  • service_secret_key
    Node’s private key (hex) for signing service transactions


Local connection parameters.

  • max_incoming_connections
    Maximum number of incoming connections
  • max_outgoing_connections
    Maximum number of outgoing connections
  • tcp_nodelay
    Activates of the NODELAY algorithm from the TCP stack (see RFC2126)
  • tcp_keep_alive Enables keep-alive and sets the idle time interval (ms) for the TCP stack (see [RFC 1122][rfc1122]). Keep-alive will be disabled if this configuration is not set (default behavior).
  • tcp_connect_retry_timeout
    Timeout interval (ms) between reconnection attempts
  • tcp_connect_max_retries Maximum number of reconnection attempts


API configuration parameters.

  • state_update_timeout
    Timeout interval (ms) to update info about connected peers
  • public_api_address
    Listen address for public API endpoints
  • private_api_address
    Listen address for private API endpoints
  • public_allow_origin
    Sets up the CORS headers for public API endpoints. The parameter can take any of the three forms:

    • "*" enables requests from all origins
    • Origin string (e.g., "") enables requests from a single specific origin
    • An array of origin strings (e.g., ["", ""]) enables requests from any of the specified origins
    • private_allow_origin Sets up the CORS headers for private API endpoints. Syntax is the same as for public_allow_origin.


If allow_origin parameters are not specified, CORS headers are not added to any requests, which can lead to requests from external origins being improperly processed by user agents with the CORS support (such as web browsers). However, you can easily avoid this by passing the public API of an Exonum node through the web server delivering web assets (for example, Nginx). In this case, the requests to API would be same-origin, so CORS restrictions would not apply.


Parameters that determine the maximum number of events that may be placed into the event queue of each type:

  • api_requests_capacity Maximum number of queued API requests.
  • internal_events_capacity Maximum number of queued internal events.
  • network_events_capacity Maximum number of queued incoming network messages.
  • network_requests_capacity Maximum number of queued outgoing network messages.


Service-specific parameters under the keys corresponding to service_names of the blockchain services.

Changing Configuration

Global parameters should be changed by using the global variables updater service. The service ensures that the configuration updates are synchronized among nodes in the network. Changing global parameters by editing the configuration file is inadmissible as this may cause improper behavior of the node. Modifying global parameters by the configuration file editing is admissible only before the genesis block is created.

Local parameters may be changed by editing the configuration file and restarting the node to apply changes. In certain cases additional actions may be required to keep the system operational.


To keep a node operating when changing its validator key, you also need to update the corresponding global variable (the list of validator keys) using the global variables updater service.