Network Map Overview

The network map is a collection of signed NodeInfo objects. Each NodeInfo is signed by the node it represents and thus cannot be tampered with. It forms the set of reachable nodes in a network. A node can receive these objects from two sources:

• A network map server that speaks a simple HTTP based protocol.
• The additional-node-infos directory within the node’s directory.

The network map server also distributes the parameters file that define values for various settings that all nodes need to agree on to remain in sync.

HTTP network map protocol

If the node is configured to connect with a network using the networkServices section of the config, then it first uploads its own signed NodeInfo to the server at the networkMapUrl (and each time it changes on startup) and then proceeds to download the entire network map from the same server. The network map consists of a list of NodeInfo hashes. The node periodically polls for the network map (based on the HTTP cache expiry header) and any new entries are downloaded and cached. Entries which no longer exist are deleted from the node’s cache.

The set of REST end-points for the Network Map Service are as follows. This defines the first commited version of the Corda Network Map protocol.

In addition to the above the Corda Enterprise Network Manager provides a number of additional features available via a REST interface. These are not used by the node itself, but either zone or node operators for information and debugging.

HTTP is used for the Network Map Service instead of Corda’s own AMQP based peer to peer messaging protocol to enable the server to be placed behind caching content delivery networks like Cloudflare, Akamai, Amazon Cloudfront and so on. By using industrial HTTP cache networks the map server can be shielded from DoS attacks more effectively. Additionally, for the case of distributing small files that rarely change, HTTP is a well understood and optimised protocol. Corda’s own protocol is designed for complex multi-way conversations between authenticated identities using signed binary messages separated into parallel and nested flows, which isn’t necessary for network map distribution.

Node Info

The node info consists the following data:

• addresses: List of network addresses (including port numbers) under which the node is accessible.

• legalIdentitiesAndCerts: List of legal identities (with their certificates) registered at the node.

• platformVersion: Platform version of the node.

• serial: Serial number of this node info file.

The additional-node-infos directory

Alongside the HTTP Network Map Service, or as a replacement if the node isn’t connected to one, the node polls the contents of the additional-node-infos directory located in its base directory. Each file is expected to be the same signed NodeInfo object that the Network Map Service vends. These are automatically added to the node’s cache and can be used to supplement or replace the HTTP network map. If the same node is advertised through both mechanisms then the latest one is taken.

On startup the node generates its own signed node info file, filename of the format nodeInfo-${hash}. It can also be generated using the --just-generate-node-info command line flag without starting the node. To create a simple network without the HTTP Network Map Service simply place this file in the additional-node-infos directory of every node that’s part of this network. For example, a simple way to do this is to use rsync.

Usually, test networks have a structure that is known ahead of time. For the creation of such networks we provide a network-bootstrapper tool. This tool pre-generates node configuration directories if given the IP addresses/domain names of each machine in the network. The generated node directories contain the NodeInfos for every other node on the network, along with the network parameters file and identity certificates. Generated nodes do not need to all be online at once - an offline node that isn’t being interacted with doesn’t impact the network in any way. So a test cluster generated like this can be sized for the maximum size you may need, and then scaled up and down as necessary.

Network parameters

Network parameters are a set of values that every node participating in the network needs to agree on and use to correctly interoperate with each other. They can be thought of as an encapsulation of all aspects of a Corda deployment on which reasonable people may disagree. Whilst other blockchain/DLT systems typically require a source code fork to alter various constants (like the total number of coins in a cryptocurrency, port numbers to use etc), in Corda we have refactored these sorts of decisions out into a separate file and allow “network operators” to make decisions about them. The operator signs a data structure that contains the values and they are distributed along with the network map. Tools are provided to gain user opt-in consent to a new version of the parameters and ensure everyone switches to them at the same time.

If the node is using the HTTP Network Map Service then on first startup it will download the signed network parameters, cache it in a network-parameters file and apply them on the node.

If the node isn’t using a HTTP Network Map Service then it’s expected the signed file is provided by some other means. For such a scenario there is the network bootstrapper tool which in addition to generating the network parameters file also distributes the node info files to the node directories.

The current set of network parameters:

• minimumPlatformVersion: The minimum platform version that the nodes must be running. Any node which is below this will not start.

• notaries: List of identity and validation type (either validating or non-validating) of the notaries which are permitted in the network.

• maxMessageSize: Maximum allowed size in bytes of an individual message sent over the wire.

• maxTransactionSize: Maximum allowed size in bytes of a transaction. This is the size of the transaction object and its attachments.

• modifiedTime: The time when the network parameters were last modified by the network operator.

• epoch: Version number of the network parameters. Starting from 1, this will always increment whenever any of the parameters change.

• whitelistedContractImplementations: List of whitelisted versions of contract code. For each contract class there is a list of hashes of the approved CorDapp jar versions containing that contract. Read more about contract constraints in the contract constraints doc. See Contract Whitelist Generation for how to configure this in the network parameters configuration file.

• eventHorizon: Time after which nodes are considered to be unresponsive and removed from network map. Nodes republish their NodeInfo on a regular interval. Network map treats that as a heartbeat from the node.

More parameters may be added in future releases to regulate things like allowed port numbers, how long a node can be offline before it is evicted from the network, whether or not IPv6 connectivity is required for members, required cryptographic algorithms and rollout schedules (e.g. for moving to post quantum cryptography), parameters related to SGX and so on.

Network parameters update process

In case of the need to change network parameters Corda network operator will start the update process. There are many reasons that may lead to this decision: adding a notary, setting new fields that were added to enable smooth network interoperability, or a change of the existing compatibility constants is required, for example.

To synchronize all nodes in the network to use the new set of the network parameters two RPC methods are provided. The process requires human interaction and approval of the change, so node operators can review the differences before agreeing to them.

When the update is about to happen the Network Map Service starts to advertise the additional information with the usual network map data. It includes new network parameters hash, description of the change and the update deadline. Nodes query the network map server for the new set of parameters.

The fact a new set of parameters is being advertised shows up in the node logs with the message “Downloaded new network parameters”, and programs connected via RPC can receive ParametersUpdateInfo by using the CordaRPCOps.networkParametersFeed method. Typically a network operator would also email node operators to let them know about the details of the impending change, along with the justification, how to object, deadlines and so on.

The node administrator can review the change and decide if they are going to accept it. The approval should be do before the update Deadline. Nodes that don’t approve before the deadline will likely be removed from the network map by the network operator, but that is a decision that is left to the operator’s discretion. For example the operator might also choose to change the deadline instead.

If the network operator starts advertising a different set of new parameters then that new set overrides the previous set. Only the latest update can be accepted.

To send back parameters approval to the network operator, the RPC method fun acceptNewNetworkParameters(parametersHash: SecureHash) has to be called with parametersHash from the update. Note that approval cannot be undone. You can do this via the Corda shell:

run acceptNewNetworkParameters parametersHash: "ba19fc1b9e9c1c7cbea712efda5f78b53ae4e5d123c89d02c9da44ec50e9c17d"

If the administrator does not accept the update then next time the node polls network map after the deadline, the advertised network parameters will be the updated ones. The previous set of parameters will no longer be valid. At this point the node will automatically shutdown and will require the node operator to bring it back again.

Node’s host IP address

The Network Map Service provides an endpoint that can be used to determine the IP address of the querying host. This is useful especially when dealing with node’s deployment in environments with IP address translation.