Connection Options

Audience: Architects, administrators, application and smart contract developers

Connection options are used in conjunction with a connection profile to control precisely how a gateway interacts with a network. Using a gateway allows an application to focus on business logic rather than network topology.

In this topic, we’re going to cover:

Scenario

A connection option specifies a particular aspect of a gateway’s behaviour. Gateways are important for many reasons, the primary being to allow an application to focus on business logic and smart contracts, while it manages interactions with the many components of a network.

profile.scenario The different interaction points where connection options control behaviour. These options are explained fully in the text.

One example of a connection option might be to specify that the gateway used by the issue application should use identity Isabella to submit transactions to the papernet network. Another might be that a gateway should wait for all three nodes from MagnetoCorp to confirm a transaction has been committed returning control. Connection options allow applications to specify the precise behaviour of a gateway’s interaction with the network. Without a gateway, applications need to do a lot more work; gateways save you time, make your application more readable, and less error prone.

Usage

We’ll describe the full set of connection options available to an application in a moment; let’s first see how they are specified by the sample MagnetoCorp issue application:

const userName = 'User1@org1.example.com';
const wallet = new FileSystemWallet('../identity/user/isabella/wallet');

const connectionOptions = {
  identity: userName,
  wallet: wallet,
  eventHandlerOptions: {
    commitTimeout: 100,
    strategy: EventStrategies.MSPID_SCOPE_ANYFORTX
    }
  };

await gateway.connect(connectionProfile, connectionOptions);

See how the identity and wallet options are simple properties of the connectionOptions object. They have values userName and wallet respectively, which were set earlier in the code. Contrast these options with the eventHandlerOptions option which is an object in its own right. It has two properties: commitTimeout: 100 (measured in seconds) and strategy: EventStrategies.MSPID_SCOPE_ANYFORTX.

See how connectionOptions is passed to a gateway as a complement to connectionProfile; the network is identified by the connection profile and the options specify precisely how the gateway should interact with it. Let’s now look at the available options.

Options

Here’s a list of the available options and what they do.

  • wallet identifies the wallet that will be used by the gateway on behalf of the application. See interaction 1; the wallet is specified by the application, but it’s actually the gateway that retrieves identities from it.

    A wallet must be specified; the most important decision is the type of wallet to use, whether that’s file system, in-memory, HSM or database.

  • identity is the user identity that the application will use from wallet. See interaction 2a; the user identity is specified by the application and represents the user of the application, Isabella, 2b. The identity is actually retrieved by the gateway.

    In our example, Isabella’s identity will be used by different MSPs (2c, 2d) to identify her as being from MagnetoCorp, and having a particular role within it. These two facts will correspondingly determine her permission over resources, such as being able to read and write the ledger, for example.

    A user identity must be specified. As you can see, this identity is fundamental to the idea that Hyperledger Fabric is a permissioned network – all actors have an identity, including applications, peers and orderers, which determines their control over resources. You can read more about this idea in the membership services topic.

  • clientTlsIdentity is the identity that is retrieved from a wallet (3a) and used for secure communications (3b) between the gateway and different channel components, such as peers and orderers.

    Note that this identity is different to the user identity. Even though clientTlsIdentity is important for secure communications, it is not as foundational as the user identity because its scope does not extend beyond secure network communications.

    clientTlsIdentity is optional. You are advised to set it in production environments. You should always use a different clientTlsIdentity to identity because these identities have very different meanings and lifecycles. For example, if your clientTlsIdentity was compromised, then so would your identity; it’s more secure to keep them separate.

  • eventHandlerOptions.commitTimeout is optional. It specifies, in seconds, the maximum amount of time the gateway should wait for a transaction to be committed by any peer (4a) before returning control to the application. The set of peers to use for notification is determined by the eventHandlerOptions.strategy option. If a commitTimeout is not specified, the gateway will use a timeout of 300 seconds.

  • eventHandlerOptions.strategy is optional. It identifies the set of peers that a gateway should use to listen for notification that a transaction has been committed. For example, whether to listen for a single peer, or all peers, from its organization. It can take one of the following values:

    • EventStrategies.MSPID_SCOPE_ANYFORTX Listen for any peer within the user’s organization. In our example, see interaction points 4b; any of peer 1, peer 2 or peer 3 from MagnetoCorp can notify the gateway.

    • EventStrategies.MSPID_SCOPE_ALLFORTX This is the default value. Listen for all peers within the user’s organization. In our example peer, see interaction point 4b. All peers from MagnetoCorp must all have notified the gateway; peer 1, peer 2 and peer 3. Peers are only counted if they are known/discovered and available; peers that are stopped or have failed are not included.

    • EventStrategies.NETWORK_SCOPE_ANYFORTX Listen for any peer within the entire network channel. In our example, see interaction points 4b and 4c; any of peer 1-3 from MagnetoCorp or peer 7-9 of DigiBank can notify the gateway.

    • EventStrategies.NETWORK_SCOPE_ALLFORTX Listen for all peers within the entire network channel. In our example, see interaction points 4b and 4c. All peers from MagnetoCorp and DigiBank must notify the gateway; peers 1-3 and peers 7-9. Peers are only counted if they are known/discovered and available; peers that are stopped or have failed are not included.

    • <PluginEventHandlerFunction> The name of a user-defined event handler. This allows a user to define their own logic for event handling. See how to define a plugin event handler, and examine a sample handler.

      A user-defined event handler is only necessary if you have very specific event handling requirements; in general, one of the built-in event strategies will be sufficient. An example of a user-defined event handler might be to wait for more than half the peers in an organization to confirm a transaction has been committed.

      If you do specify a user-defined event handler, it does not affect your application logic; it is quite separate from it. The handler is called by the SDK during processing; it decides when to call it, and uses its results to select which peers to use for event notification. The application receives control when the SDK has finished its processing.

      If a user-defined event handler is not specified then the default values for EventStrategies are used.

  • discovery.enabled is optional and has possible values true or false. The default is true. It determines whether the gateway uses service discovery to augment the network topology specified in the connection profile. See interaction point 6; peer’s gossip information used by the gateway.

    This value will be overridden by the INITIALIIZE-WITH-DISCOVERY environment variable, which can be set to true or false.

  • discovery.asLocalhost is optional and has possible values true or false. The default is true. It determines whether IP addresses found during service discovery are translated from the docker network to the local host.

    Typically developers will write applications that use docker containers for their network components such as peers, orderers and CAs, but that do not run in docker containers themselves. This is why true is the default; in production environments, applications will likely run in docker containers in the same manner as network components and therefore address translation is not required. In this case, applications should either explicitly specify false or use the environment variable override.

    This value will be overridden by the DISCOVERY-AS-LOCALHOST environment variable, which can be set to true or false.

Considerations

The following list of considerations is helpful when deciding how to choose connection options.

  • eventHandlerOptions.commitTimeout and eventHandlerOptions.strategy work together. For example, commitTimeout: 100 and strategy: EventStrategies.MSPID_SCOPE_ANYFORTX means that the gateway will wait for up to 100 seconds for any peer to confirm a transaction has been committed. In contrast, specifying strategy: EventStrategies.NETWORK_SCOPE_ALLFORTX means that the gateway will wait up to 100 seconds for all peers in all organizations.

  • The default value of eventHandlerOptions.strategy: EventStrategies.MSPID_SCOPE_ALLFORTX will wait for all peers in the application’s organization to commit the transaction. This is a good default because applications can be sure that all their peers have an up-to-date copy of the ledger, minimizing concurrency issues

    However, as the number of peers in an organization grows, it becomes a little unnecessary to wait for all peers, in which case using a pluggable event handler can provide a more efficient strategy. For example the same set of peers could be used to submit transactions and listen for notifications, on the safe assumption that consensus will keep all ledgers synchronized.

  • Service discovery requires clientTlsIdentity to be set. That’s because the peers exchanging information with an application need to be confident that they are exchanging information with entities they trust. If clientTlsIdentity is not set, then discovery will not be obeyed, regardless of whether or not it is set.

  • Although applications can set connection options when they connect to the gateway, it can be necessary for these options to be overridden by an administrator. That’s because options relate to network interactions, which can vary over time. For example, an administrator trying to understand the effect of using service discovery on network performance.

    A good approach is to define application overrides in a configuration file which is read by the application when it configures its connection to the gateway.

    Because the discovery options enabled and asLocalHost are most frequently required to be overridden by administrators, the environment variables INITIALIIZE-WITH-DISCOVERY and DISCOVERY-AS-LOCALHOST are provided for convenience. The administrator should set these in the production runtime environment of the application, which will most likely be a docker container.