API Configuration

A domain node exposes two main APIs: the admin-api and the public-api, while the participant node exposes the ledger-api and the admin-api. In this section, we will explain what the APIs do and how they can be configured.

Default Ports

Canton assigns ports automatically for all the APIs of all the configured nodes if the port has not been configured explicitly. The ports are allocated according to the following scheme:

/** Participant node default ports */
val ledgerApiPort = defaultPortStart(4001)
val participantAdminApiPort = defaultPortStart(4002)

/** Domain node default ports */
val domainPublicApiPort = defaultPortStart(4201)
val domainAdminApiPort = defaultPortStart(4202)

/** External sequencer node default ports (enterprise-only) */
val sequencerPublicApiPort = defaultPortStart(4401)
val sequencerAdminApiPort = defaultPortStart(4402)

/** External mediator node default port (enterprise-only) */
val mediatorAdminApiPort = defaultPortStart(4602)

/** Domain node default ports */
val domainManagerAdminApiPort = defaultPortStart(4801)

/** External sequencer node x default ports (enterprise-only) */
val sequencerXPublicApiPort = defaultPortStart(5001)
val sequencerXAdminApiPort = defaultPortStart(5002)

/** External mediator node x default port (enterprise-only) */
val mediatorXAdminApiPort = defaultPortStart(5202)

/** Increase the default port number for each new instance by portStep */
private val portStep = 10

Administration API

The nature and scope of the admin api on participant and domain nodes has some overlap. As an example, you will find the same key management commands on the domain and the participant node API, whereas the participant has different commands to connect to several domains.

The configuration currently is simple (see the TLS example below) and just takes an address and a port. The address defaults to and a default port is assigned if not explicitly configured.

You should not expose the admin-api publicly in an unsecured way as it serves administrative purposes only.

TLS Configuration

Both, the Ledger API and the admin API provide the same TLS capabilities and can be configured using the same configuration directives. TLS provides end-to-end channel encryption between the server and client, and depending on the settings, server or mutual authentication.

A full configuration example is given by

canton.participants.participant4.ledger-api {
  address = "" // IP / DNS must be SAN of certificate to allow local connections from the canton process
  port = 5041
  tls {
    // the certificate to be used by the server
    cert-chain-file = "./tls/ledger-api.crt"
    // private key of the server
    private-key-file = "./tls/ledger-api.pem"
    // trust collection, which means that all client certificates will be verified using the trusted
    // certificates in this store. if omitted, the JVM default trust store is used.
    trust-collection-file = "./tls/root-ca.crt"
    // define whether clients need to authenticate as well (default not)
    client-auth = {
      // none, optional and require are supported
      type = require
      // If clients are required to authenticate as well, we need to provide a client
      // certificate and the key, as Canton has internal processes that need to connect to these
      // APIs. If the server certificate is trusted by the trust-collection, then you can
      // just use the server certificates. Otherwise, you need to create separate ones.
      admin-client {
        cert-chain-file = "./tls/admin-client.crt"
        private-key-file = "./tls/admin-client.pem"
    // minimum-server-protocol-version = ...
    // ciphers = ...

These TLS settings allow a connecting client to ensure that it is talking to the right server. In this example, we have also enabled client authentication, which means that the client needs to present a valid certificate (and have the corresponding private key). The certificate is valid if it has been signed by a key in the trust store.

The trust-collection-file allows us to provide a file based trust store. If omitted, the system will default to the built-in JVM trust store. The file must contain all client certificates (or parent certificates which were used to sign the client certificate) who are trusted to use the API. The format is just a collection of PEM certificates (in the right order or hierarchy), not a java based trust store.

If you want to use mTLS on the Admin API, you must sign the client certificates with the certificate defined in the trust-collection-file.

In order to operate the server just with server-side authentication, you can just omit the section on client-auth. However, if client-auth is set to require, then Canton also requires a client certificate, as various Canton internal processes will connect to the process itself through the API.

All the private keys need to be in the pkcs8 PEM format.

By default, Canton only uses new versions of TLS and strong ciphers. You can also override the default settings using the variables ciphers and protocols. If you set these settings to null, the default JVM values will be used.


Error messages on TLS issues provided by the networking library netty are less than optimal. If you are struggling with setting up TLS, please enable DEBUG logging on the io.netty logger.

Note that the configuration hierarchy for a remote participant console is slightly different from the in-process console or participant shown above.

If you need to create a set of testing TLS certificates, you can use the following openssl commands:

# include certs-common.sh from config/tls
. "$(dirname "${BASH_SOURCE[0]}")/certs-common.sh"

# create root certificate such that we can issue self-signed certs
create_key "root-ca"
create_certificate "root-ca" "/O=TESTING/OU=ROOT CA/emailAddress=canton@digitalasset.com"
#print_certificate "root-ca"

# create public api certificate
create_key "public-api"
create_csr "public-api" "/O=TESTING/OU=DOMAIN/CN=localhost/emailAddress=canton@digitalasset.com" "DNS:localhost,IP:"
sign_csr "public-api" "root-ca"
print_certificate "public-api"

# create participant ledger-api certificate
create_key "ledger-api"
create_csr "ledger-api" "/O=TESTING/OU=PARTICIPANT/CN=localhost/emailAddress=canton@digitalasset.com" "DNS:localhost,IP:"
sign_csr "ledger-api" "root-ca"

# create participant admin-api certificate
create_key "admin-api"
create_csr "admin-api" "/O=TESTING/OU=PARTICIPANT ADMIN/CN=localhost/emailAddress=canton@digitalasset.com" "DNS:localhost,IP:"
sign_csr "admin-api" "root-ca"

# create participant client key and certificate
create_key "admin-client"
create_csr "admin-client" "/O=TESTING/OU=PARTICIPANT ADMIN CLIENT/CN=localhost/emailAddress=canton@digitalasset.com"
sign_csr "admin-client" "root-ca"
print_certificate "admin-client"

If you are having problems with SSL connectivity, you can enable SSL debugging by adding the following flag to the command line when starting Canton:

bin/canton -Djavax.net.debug=all

This will enable detailed SSL debugging information to be printed to the console, which can help you diagnose and troubleshoot any problems you may be experiencing. It is recommended to only enable this flag when needed, as the output can be very verbose and may impact the performance of your application.

Keep Alive

In order to prevent load-balancers or firewalls from terminating long running RPC calls in the event of some silence on the connection, all GRPC connections enable keep-alive by default. An example configuration for an adjusted setting is given below:

canton.participants.participant2 {
  admin-api {
    address = ""
    port = 5022
    keep-alive-server {
      time = 40s
      timeout = 20s
      permit-keep-alive-time = 20s
  sequencer-client {
    keep-alive-client {
      time = 60s
      timeout = 30s

GRPC client connections are configured with keep-alive-client, with two settings: time, and timeout. The effect of the time and timeout settings are described in the GRPC documentation.

Servers can additionally change another setting: permit-keep-alive-time. This specifies the most aggressive keep-alive time that a client is permitted to use. If a client uses keep-alive time that is more aggressive than the permit-keep-alive-time, the connection will be terminated with a GOAWAY frame with “too_many_pings” as the debug data. This setting is described in more detail in the GRPC documentation and GRPC manual page.

Max Inbound Message Size

The APIs exposed by both the participant (ledger API and admin API) as well as by the domain (public API and admin API) have an upper limit on incoming message size. To increase this limit to accommodate larger payloads, the flag max-inbound-message-size has to be set for the respective API to the maximum message size in bytes.

For example, to configure a participant’s ledger API limit to 20MB:

canton.participants.participant2.ledger-api {
  address = ""
  port = 5021
  max-inbound-message-size = 20971520

Participant Configuration

Ledger Api

The configuration of the ledger API is similar to the admin API configuration, except that the group starts with ledger-api instead of admin-api.

JWT Authorization

The Ledger Api supports JWT based authorization checks as described in the Authorization documentation.

In order to enable JWT authorization checks, your safe configuration options are

_shared {
  ledger-api {
    auth-services = [{
      // type can be
      //   jwt-rs-256-crt
      //   jwt-es-256-crt
      //   jwt-es-512-crt
      type = jwt-rs-256-crt
      // we need a certificate file (abcd.cert)
      certificate = ${JWT_CERTIFICATE_FILE}
  • jwt-rs-256-crt. The participant will expect all tokens to be signed with RS256 (RSA Signature with SHA-256) with the public key loaded from the given X.509 certificate file. Both PEM-encoded certificates (text files starting with -----BEGIN CERTIFICATE-----) and DER-encoded certificates (binary files) are supported.
  • jwt-es-256-crt. The participant will expect all tokens to be signed with ES256 (ECDSA using P-256 and SHA-256) with the public key loaded from the given X.509 certificate file. Both PEM-encoded certificates (text files starting with -----BEGIN CERTIFICATE-----) and DER-encoded certificates (binary files) are supported.
  • jwt-es-512-crt. The participant will expect all tokens to be signed with ES512 (ECDSA using P-521 and SHA-512) with the public key loaded from the given X.509 certificate file. Both PEM-encoded certificates (text files starting with -----BEGIN CERTIFICATE-----) and DER-encoded certificates (binary files) are supported.

Instead of specifying the path to a certificate, you can also a JWKS URL. In that case, the participant will expect all tokens to be signed with RS256 (RSA Signature with SHA-256) with the public key loaded from the given JWKS URL.

_shared {
  ledger-api {
    auth-services = [{
      type = jwt-rs-256-jwks
      // we need a URL to a jwks key, e.g. https://path.to/jwks.key
      url = ${JWT_URL}


For testing purposes only, you can also specify a shared secret. In that case, the participant will expect all tokens to be signed with HMAC256 with the given plaintext secret. This is not considered safe for production.

_shared {
  ledger-api {
    auth-services = [{
      type = unsafe-jwt-hmac-256
      secret = "not-safe-for-production"


To prevent man-in-the-middle attacks, it is highly recommended to use TLS with server authentication as described in TLS Configuration for any request sent to the Ledger API in production.

Note that you can define multiple authorization plugins. If more than one is defined, the system will use the claim of the first auth plugin that does not return Unauthorized.

If no authorization plugins are defined, a default (wildcard) authorization method is used.

Leeway Parameters for JWT Authorization

You can define leeway parameters for authorization using JWT tokens. An authorization which fails due to clock skew between the signing and the verification of the tokens can be eased by specifying a leeway window in which the token should still be considered valid. Leeway can be defined either specifically for the Expiration Time (“exp”), Not Before (“nbf”) and Issued At (“iat”) claims of the token or by a default value for all three. The values defining the leeway for each of the three specific fields override the default value if present. The leeway parameters should be given in seconds and can be defined as in the example configuration below:

canton.participants.participant.parameters.ledger-api-server-parameters.jwt-timestamp-leeway {
    default = 5
    expires-at = 10
    issued-at = 15
    not-before = 20

Configuring the Target Audience for JWT Authorization

The default audience (aud field in the audience based token) for authenticating on the Ledger Api using JWT is https://daml.com/participant/jwt/aud/participant/${participantId}. Other audiences can be configured explicitly using the custom target audience configuration option:

canton {
  participants {
    participant {
      ledger-api {
        auth-services = [{
          type = jwt-rs-256-jwks
          url = "https://target.audience.url/jwks.json"
          target-audience = "https://rewrite.target.audience.url"

Configuring the Target Scope for JWT Authorization

The default scope (scope field in the scope based access token) for authenticating on the Ledger API using JWT is daml_ledger_api.

Other scopes can be configured explicitly using the custom target scope configuration option:

canton {
  participants {
    participant {
      ledger-api {
        auth-services = [{
          type = jwt-rs-256-jwks
          url = "https://some.url/jwks.json"
          target-scope = "custom/Scope-5:with_special_characters"

Target scope can be any case-sensitive string containing alphanumeric characters, hyphens, slashes, colons and underscores. Either the target-scope or the target-audience parameter can be configured individually, but not both at the same time.

Ledger API Caches

The max-contract-state-cache-size and max-contract-key-state-cache-size parameters control the sizes of the ledger API contract and contract key caches, respectively. Modifying these parameters changes the likelihood that a transaction using a contract or a contract-key that was recently accessed (created or read) can still find it in the memory, rather than needing to query it from the database. Larger caches might be of interest when there is a big pool of ambient contracts that are consistently being fetched or used for non-consuming exercises. Larger caches can also benefit use cases where a big pool of contracts rotates through a create -> archive -> create-successor cycle. Consider adjusting these parameters explicitly if the performance of your specific workflow depends on large caches.

canton.participants.participant.ledger-api.index-service {
    max-contract-state-cache-size = 100000      // default 1e4
    max-contract-key-state-cache-size = 100000  // default 1e4

Max Transactions in the In-Memory Fan-Out

The max-transactions-in-memory-fan-out-buffer-size parameter controls the size of the in-memory fan-out buffer. This buffer allows serving the transaction streams from memory as they are finalized, rather than from the database. Make sure this buffer is large enough so applications are less likely to have to stream transactions from the database. In most cases, a 10s buffer works well. For example, if you expect a throughput of 20 tx/s, set this number to 200. The new default setting of 1000 assumes 100 tx/s. Consider adjusting these parameters explicitly if the performance of your workflow foresees transaction rates larger than 100 tx/s.

canton.participants.participant.ledger-api.index-service {
    max-transactions-in-memory-fan-out-buffer-size = 10000 // default 1000

Domain Configurations

Public Api

The domain configuration requires the same configuration of the admin-api as the participant. Next to the admin-api, we need to configure the public-api, which is the api where all participants connect.

Authentication Token

Authentication of the restricted services is built into the public sequencer api, leveraging the participant signing keys. You don’t need to do anything in order to set this up; it is enforced automatically and can’t be turned off. The same mechanism is used to check the authentication of the domain topology manager and the mediator.

The token is generated during the handshake between the node and the sequencer. By default, it is valid for one hour. The nodes automatically renew the token in the background before it expires. The lifetime of the tokens and of the nonce can be reconfigured using

canton.domains.mydomain.public-api {
    token-expiration-time = 60m
    nonce-expiration-time = 1m

However, we suggest keeping the default values.

TLS Encryption

As with the admin-api, network traffic can (and should) be encrypted using TLS. This is particularly crucial for the Public API.

An example configuration section which enables TLS encryption and server-side TLS authentication is given by

canton.domains.acme.public-api {
  port = 5028
  address = localhost // defaults to
  tls {
    cert-chain-file = "./tls/public-api.crt"
    private-key-file = "./tls/public-api.pem"
    // minimum-server-protocol-version = TLSv1.3, optional argument
    // ciphers = null // use null to default to JVM ciphers

If TLS is used on the server side with a self-signed certificate, we need to pass the certificate chain during the connect call of the participant. Otherwise, the default root certificates of the Java runtime will be used. An example would be:

  domainAlias = "acme",
  connection = s"https://$hostname:$port",
  certificatesPath = certs, // path to certificate chain file (.pem) of server

Usage of native libraries by Netty

Canton ships with native libraries (for some processor architectures: x86_64, ARM64, S390_64) so that the Netty network access library can take advantage of epoll on Linux, generally leading to improved performance and less pressure on the JVM garbage collector. The available native is picked up automatically and it falls back to the standard NIO library if running on unsupported operating systems or architectures.

Furthermore, the usage of the native library can also be switched off by setting the following: -Dio.netty.transport.noNative=true. Even when this is expected, falling back to NIO might lead to a warning being emitted at DEBUG level on your log.