Sequencer Connections

Any member of a Canton network, whether a participant, mediator or topology manager, connects to the domain by virtue of connecting to a sequencer of that domain (there can be multiple thereof). The component managing this connection is called the SequencerClient.

A participant can connect to multiple domains (preview) simultaneously, but a mediator or topology manager will only connect to a single domain. Therefore, managing the sequencer connections of a participant differs slightly from managing a mediator or topology manager connection.

In the following sections, we will explain how to manage such sequencer connections.

Participant Connections

The domain connectivity commands allow the administrator of a Canton node to manage connectivity to domains. Generally, the key command to add new connections is given by the :ref:` register command <participant.domains.register>`. While this is the command with the broadest ability to configure the connection, there are a few convenience macros that combine a series of steps to simplify administrative operations.

Connect Using Macros

Connect to Local Sequencers

When a participant should connect to a sequencer or domain that is running in the same process, you can use the domains.connect_local macro and simply provide the reference to the local node.

@ participant1.domains.connect_local(sequencer1)

The connect_local macro will generate the appropriate configuration settings for the provided sequencer and instruct the participant to connect to it using the register command.

Please note that you can also pass a local DomainReference to the connect_local call in case you are running an embedded domain.

Connect to Remote Sequencers

If you are connecting to a sequencer that is running on a remote host, you need to know the address and port the sequencer is configured to listen to. You can print out the port the sequencer is listening to using:

@ sequencer1.config.publicApi.port
res2: Port = 15057

You can also check that the address is set such that remote processes can connect to it:

@ sequencer1.config.publicApi.address
res3: String = "0.0.0.0"

By default, a sequencer will listen to 127.0.0.1, which is localhost. These is a safe default and it means that only processes running locally can connect to the sequencer (it is also set by default for the Ledger API and the Admin API). If you want to support remote processes connecting to the given sequencer, you need to explicitly configure it using:

// enable access of remote processes to the sequencer
canton.sequencers.sequencer1.public-api.address = 0.0.0.0

In this example, sequencer1 and sequencer2 are configured without TLS, whereas sequencer3 is configured to use TLS:

@ sequencer3.config.publicApi.tls
res4: Option[TlsBaseServerConfig] = Some(
  value = TlsBaseServerConfig(
    certChainFile = ExistingFile(file = ./tls/sequencer3-127.0.0.1.crt),
    privateKeyFile = ExistingFile(file = ./tls/sequencer3-127.0.0.1.pem),
    minimumServerProtocolVersion = Some(value = "TLSv1.2"),
    ciphers = Some(
      value = List(
        "TLS_AES_256_GCM_SHA384",
        "TLS_CHACHA20_POLY1305_SHA256",
        "TLS_AES_128_GCM_SHA256",
        "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
        "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256"
      )
    )
  )
)

To connect to sequencer3 using the connect macro, we need to create an URL string:

@ val port = sequencer3.config.publicApi.port
port : Port = 15053

@ val url = s"https://127.0.0.1:${port}"
url : String = "https://127.0.0.1:15053"

Please note that you need to adjust the https to http if you are not using TLS on the public sequencer Api. If the sequencer is using TLS certificates (e.g. self-signed) that cannot be automatically validated using your JVMs trust store, you have to provide the custom certificate such that the client can verify the sequencer public API TLS certificate. Let’s assume that this root certificate is given by:

@ val certificatesPath = "tls/root-ca.crt"
certificatesPath : String = "tls/root-ca.crt"

You can now connect the participant to the sequencer using:

@ participant2.domains.connect("mydomain", connection = url, certificatesPath = certificatesPath)
res8: DomainConnectionConfig = DomainConnectionConfig(
  domain = Domain 'mydomain',
  sequencerConnection = GrpcSequencerConnection(
    endpoints = https://127.0.0.1:15053,
    transportSecurity = true,
    customTrustCertificates = Some(2d2d2d2d2d42)
  ),
  manualConnect = false,
  domainId = None(),
  priority = 0,
  initialRetryDelay = None(),
  maxRetryDelay = None()
)

Connect to High-Availability Sequencers

Important

This feature is only available in Canton Enterprise

The Enterprise version of Canton lets you connect a participant to multiple sequencers for the purpose of high availability. If one sequencer shuts down, the participant will then automatically fail over to the second sequencer.

Such a connection can be configured using the connect_multi:

@ participant3.domains.connect_multi("mydomain", Seq(sequencer1, sequencer2))
res9: DomainConnectionConfig = DomainConnectionConfig(
  domain = Domain 'mydomain',
  sequencerConnection = GrpcSequencerConnection(
    endpoints = Seq(http://0.0.0.0:15057, http://127.0.0.1:15055),
    transportSecurity = false,
    customTrustCertificates = None()
  ),
  manualConnect = false,
  domainId = None(),
  priority = 0,
  initialRetryDelay = None(),
  maxRetryDelay = None()
)

In such a setting, if a sequencer node goes down, the participant will round-robin through the available list of sequencers. The reference documentation provides further information on how to connect to highly available sequencers, and the high availability guide has instructions on how to set up highly available domains.

Currently, all the sequencer connections used by a node need to be using TLS or not. A mixed mode where one sequencer is using TLS and another not is not supported.

Connect Using Register

The highest level of control over your domain connection is given by using register with a configuration of type DomainConnectionConfig. By default, the connection configuration only requires two arguments: the domain alias and the connection URL. In this guide, we’ll cover all arguments.

First, we need to associate the domain connection to an alias. An alias is an arbitrary name chosen by the operator of the participant to manage the given connection:

@ val domainAlias = "mydomain"
domainAlias : String = "mydomain"

A domain alias is just a string wrapped into the type “DomainAlias”. This is done implicitly in the console, which allows you to use a string instead.

Next, you need to create a connection description of type SequencerConnection. The public sequencer API in Canton is based on gRPC, which uses HTTP 2.0. In this example, we build the URLs by inspecting the configurations:

@ val urls = Seq(sequencer1, sequencer2).map(_.config.publicApi.port).map(port => s"http://127.0.0.1:${port}")
urls : Seq[String] = List("http://127.0.0.1:15057", "http://127.0.0.1:15055")

However, the url can also be entered as a string. A connection is then built using:

@ val sequencerConnectionWithoutHighAvailability = com.digitalasset.canton.sequencing.GrpcSequencerConnection.tryCreate(urls(0))
sequencerConnectionWithoutHighAvailability : com.digitalasset.canton.sequencing.GrpcSequencerConnection = GrpcSequencerConnection(
  endpoints = http://127.0.0.1:15057,
  transportSecurity = false,
  customTrustCertificates = None()
)

A second sequencer URL can be added using:

@ val sequencerConnection = sequencerConnectionWithoutHighAvailability.addConnection(urls(1))
sequencerConnection : com.digitalasset.canton.sequencing.SequencerConnection = GrpcSequencerConnection(
  endpoints = Seq(http://127.0.0.1:15057, http://127.0.0.1:15055),
  transportSecurity = false,
  customTrustCertificates = None()
)

While the connect macros allow you to pass in a file path as an argument for the optional TLS certificate, you need to resolve this argument and load the certificate into a ByteString when working with GrpcSequencerConnection. There is a utility function that allows you to read a certificate from a file into a ByteString such that it can be used to create an appropriate sequencer connection:

@ val certificate = com.digitalasset.canton.util.BinaryFileUtil.tryReadByteStringFromFile("tls/root-ca.crt")
certificate : com.google.protobuf.ByteString = <ByteString@383ad9d4 size=1960 contents="-----BEGIN CERTIFICATE-----\nMIIFeTCCA2GgAwIBAgI...">

@ val connectionWithTLS = com.digitalasset.canton.sequencing.GrpcSequencerConnection.tryCreate("https://daml.com", customTrustCertificates = Some(certificate))
connectionWithTLS : com.digitalasset.canton.sequencing.GrpcSequencerConnection = GrpcSequencerConnection(
  endpoints = https://daml.com:443,
  transportSecurity = true,
  customTrustCertificates = Some(2d2d2d2d2d42)
)

Next, you can assign a priority to the domain by setting the priority parameter:

@ val priority = 10 // default is 0 if not set
priority : Int = 10

This parameter is used to determine the domain to which a transaction should be sent if there are multiple domains connected (early access feature). The domain with the highest priority that can run a certain transaction will be picked.

Finally, when configuring a domain connection, the parameter manualConnect can be used when the domain should not be auto-reconnected on startup. By default, you would set:

@ val manualConnect = false
manualConnect : Boolean = false

If a domain connection is configured to be manual, it will not reconnect automatically on startup; it has to be reconnected specifically using:

@ participant3.domains.reconnect("mydomain")
res18: Boolean = true

Very security sensitive users that do not trust TLS to check for authenticity of the sequencer API can additionally pass an optional domainId of the target domain into the configuration. In this case, the participant will check that the sequencer it is connecting to can produce the cryptographic evidence that it actually is the expected domain. The domainId can be obtained from the domain manager:

@ val domainId = Some(domainManager1.id)
domainId : Some[DomainId] = Some(value = domainManager1::1220f1fe5194...)

These parameters together can be used to define a connection configuration:

@ val config = DomainConnectionConfig(domain = "mydomain", sequencerConnection, manualConnect, domainId, priority)
config : DomainConnectionConfig = DomainConnectionConfig(
  domain = Domain 'mydomain',
  sequencerConnection = GrpcSequencerConnection(
    endpoints = Seq(http://127.0.0.1:15057, http://127.0.0.1:15055),
    transportSecurity = false,
    customTrustCertificates = None()
  ),
  manualConnect = false,
  domainId = Some(domainManager1::1220f1fe5194...),
  priority = 10,
  initialRetryDelay = None(),
  maxRetryDelay = None()
)

All other parameters are expert settings and should not be used. The config object can now be used to connect a participant to a sequencer:

@ participant4.domains.register(config)

Inspect Connections

You can inspect the registered domain connections using:

@ participant2.domains.list_registered()
res22: Seq[(DomainConnectionConfig, Boolean)] = Vector(
  (
    DomainConnectionConfig(
      domain = Domain 'mydomain',
      sequencerConnection = GrpcSequencerConnection(
        endpoints = https://127.0.0.1:15053,
        transportSecurity = true,
        customTrustCertificates = Some(2d2d2d2d2d42)
      ),
      manualConnect = false,
      domainId = None(),
      priority = 0,
      initialRetryDelay = None(),
      maxRetryDelay = None()
    ),
    true
  )
)

You can also get the aliases of the currently connected domains using:

@ participant2.domains.list_connected()
res23: Seq[ListConnectedDomainsResult] = Vector(
  ListConnectedDomainsResult(
    domainAlias = Domain 'mydomain',
    domainId = domainManager1::1220f1fe5194...,
    healthy = true
  )
)

And you can inspect the configuration of a specific domain connection using:

@ participant2.domains.config("mydomain")
res24: Option[DomainConnectionConfig] = Some(
  value = DomainConnectionConfig(
    domain = Domain 'mydomain',
    sequencerConnection = GrpcSequencerConnection(
      endpoints = https://127.0.0.1:15053,
      transportSecurity = true,
      customTrustCertificates = Some(2d2d2d2d2d42)
    ),
    manualConnect = false,
    domainId = None(),
    priority = 0,
    initialRetryDelay = None(),
    maxRetryDelay = None()
  )
)

Modify Connections

Domain connection configurations can be updated using the modify function:

@ participant2.domains.modify("mydomain", _.copy(priority = 20))

The second argument is a mapping function which receives as input argument a DomainConnectionConfig and needs to return a DomainConnectionConfig. Every case class has a default copy method that allows overriding arguments.

Update a Custom TLS Trust Certificate

In some cases (in particular in test environments), you might be using self-signed certificates as a root of trust for the TLS sequencer connection. Whenever this root of trust changes, the clients need to update the custom root certificate accordingly.

This can be done through the following steps. First, you need to load the certificate from a file:

@ val certificate = com.digitalasset.canton.util.BinaryFileUtil.tryReadByteStringFromFile("tls/root-ca.crt")
certificate : com.google.protobuf.ByteString = <ByteString@208521c6 size=1960 contents="-----BEGIN CERTIFICATE-----\nMIIFeTCCA2GgAwIBAgI...">

This step loads the root certificate from a file and stores it into a variable that can be used subsequently. Next, you create a new connection object, passing in the certificate:

@ val connection = com.digitalasset.canton.sequencing.GrpcSequencerConnection.tryCreate(url, customTrustCertificates = Some(certificate))
connection : com.digitalasset.canton.sequencing.GrpcSequencerConnection = GrpcSequencerConnection(
  endpoints = https://127.0.0.1:15053,
  transportSecurity = true,
  customTrustCertificates = Some(2d2d2d2d2d42)
)

Finally, you update the sequencer connection settings on the participant node:

@ participant2.domains.modify("mydomain", _.copy(sequencerConnection=connection))

For mediators / domain managers, you can update the certificate accordingly.

Enable and Disable Connections

A participant can disconnect from a domain using:

@ participant2.domains.disconnect("mydomain")

Reconnecting to the domain can be done either on a per domain basis:

@ participant2.domains.reconnect("mydomain")
res30: Boolean = true

Or for all registered domains that are not configured to require a manual connection:

@ participant2.domains.reconnect_all()

Mediator and Domain Manager

Both the mediator and the domain manager connect to the domain using sequencer connections. The sequencer connections are configured when the nodes are initialized:

@ mediator1.mediator.help("initialize")
initialize(domainId: com.digitalasset.canton.topology.DomainId, mediatorId: com.digitalasset.canton.topology.MediatorId, domainParameters: com.digitalasset.canton.admin.api.client.data.StaticDomainParameters, sequencerConnection: com.digitalasset.canton.sequencing.SequencerConnection, topologySnapshot: Option[com.digitalasset.canton.topology.store.StoredTopologyTransactions[com.digitalasset.canton.topology.transaction.TopologyChangeOp.Positive]], cryptoType: String): com.digitalasset.canton.crypto.PublicKey
Initialize a mediator

The sequencer connection of a mediator and domain manager can be inspected using:

@ mediator1.sequencer_connection.get()
res33: Option[com.digitalasset.canton.sequencing.SequencerConnection] = Some(
  value = GrpcSequencerConnection(
    endpoints = http://0.0.0.0:15057,
    transportSecurity = false,
    customTrustCertificates = None()
  )
)

In some cases, the connection settings have to be updated. For this purpose, the two following functions can be used. First, the connection information can just be set using:

@ mediator1.sequencer_connection.set(sequencer1.sequencerConnection)

It can also be amended using:

@ mediator1.sequencer_connection.modify(_.addConnection(sequencer2.sequencerConnection))

Please note that the connection changes immediately, without requiring a restart.