Kura Adapter Configuration

The Kura protocol adapter exposes an MQTT topic hierarchy allowing Eclipse Kura™ 3 based gateways to access Eclipse Hono™’s south bound Telemetry, Event and Command & Control APIs.

The adapter is implemented as a Spring Boot application. It can be run either directly from the command line or by means of starting the corresponding Docker image created from it.

Info

The Kura adapter is deprecated and will be removed completely in Hono 2.0.0. Support for Kura version 4 and later is still available by means of Hono’s standard MQTT adapter.

Service Configuration

The following table provides an overview of the configuration variables and corresponding system properties for configuring the MQTT adapter.

OS Environment Variable
Java System Property
Mandatory Default Value Description
HONO_APP_MAXINSTANCES
hono.app.maxInstances
no #CPU cores The number of verticle instances to deploy. If not set, one verticle per processor core is deployed.
HONO_KURA_AUTHENTICATIONREQUIRED
hono.kura.authenticationRequired
no true If set to true the protocol adapter requires devices to authenticate when connecting to the adapter. The credentials provided by the device are verified using the configured Credentials Service. Devices that have failed to authenticate are not allowed to publish any data.
HONO_KURA_BINDADDRESS
hono.kura.bindAddress
no 127.0.0.1 The IP address of the network interface that the secure port should be bound to.
See Port Configuration below for details.
HONO_KURA_CERTPATH
hono.kura.certPath
no - The absolute path to the PEM file containing the certificate that the protocol adapter should use for authenticating to clients. This option must be used in conjunction with HONO_KURA_KEYPATH.
Alternatively, the HONO_KURA_KEYSTOREPATH option can be used to configure a key store containing both the key as well as the certificate.
HONO_KURA_CONTROLPREFIX
hono.kura.controlPrefix
no $EDC The topic.control-prefix to use for determining if a message published by a Kura gateway is a control message. All messages published to a topic that does not start with this prefix are considered data messages.
HONO_KURA_CTRLMSGCONTENTTYPE
hono.kura.ctrlMsgContentType
no application/vnd.eclipse.kura-control The content type to set on AMQP messages created from Kura control messages.
HONO_KURA_DATAMSGCONTENTTYPE
hono.kura.dataMsgContentType
no application/vnd.eclipse.kura-data The content type to set on AMQP messages created from Kura data messages.
HONO_KURA_DEFAULTSENABLED
hono.kura.defaultsEnabled
no true If set to true the protocol adapter uses default values registered for a device to augment messages published by the device with missing information like a content type. In particular, the protocol adapter adds default values registered for the device as (application) properties with the same name to the AMQP 1.0 messages it sends downstream to the AMQP Messaging Network.
HONO_KURA_INSECUREPORT
hono.kura.insecurePort
no - The insecure port the protocol adapter should listen on.
See Port Configuration below for details.
HONO_KURA_INSECUREPORTBINDADDRESS
hono.kura.insecurePortBindAddress
no 127.0.0.1 The IP address of the network interface that the insecure port should be bound to.
See Port Configuration below for details.
HONO_KURA_INSECUREPORTENABLED
hono.kura.insecurePortEnabled
no false If set to true the protocol adapter will open an insecure port (not secured by TLS) using either the port number set via HONO_KURA_INSECUREPORT or the default MQTT port number (1883) if not set explicitly.
See Port Configuration below for details.
HONO_KURA_KEYPATH
hono.kura.keyPath
no - The absolute path to the (PKCS8) PEM file containing the private key that the protocol adapter should use for authenticating to clients. This option must be used in conjunction with HONO_KURA_CERTPATH. Alternatively, the HONO_KURA_KEYSTOREPATH option can be used to configure a key store containing both the key as well as the certificate.
HONO_KURA_KEYSTOREPASSWORD
hono.kura.keyStorePassword
no - The password required to read the contents of the key store.
HONO_KURA_KEYSTOREPATH
hono.kura.keyStorePath
no - The absolute path to the Java key store containing the private key and certificate that the protocol adapter should use for authenticating to clients. Either this option or the HONO_KURA_KEYPATH and HONO_KURA_CERTPATH options need to be set in order to enable TLS secured connections with clients. The key store format can be either JKS or PKCS12 indicated by a .jks or .p12 file suffix respectively.
HONO_KURA_SNI
hono.kura.sni
no false Set whether the server supports Server Name Indication. By default, the server will not support SNI and the option is false. However, if set to true then the key store format , HONO_KURA_KEYSTOREPATH, should be either JKS or PKCS12 indicated by a .jks or .p12 file suffix respectively.
HONO_MQTT_MAXCONNECTIONS
hono.mqtt.maxConnections
no 0 The maximum number of concurrent connections that the protocol adapter should accept. If not set (or set to 0), the protocol adapter determines a reasonable value based on the available resources like memory and CPU.
HONO_KURA_MAXPAYLOADSIZE
hono.kura.maxPayloadSize
no 2048 The maximum allowed size of an incoming MQTT message’s payload in bytes. When a client sends a message with a larger payload, the message is discarded and the connection to the client gets closed.
HONO_KURA_NATIVETLSREQUIRED
hono.kura.nativeTlsRequired
no false The server will probe for OpenSSL on startup if a secure port is configured. By default, the server will fall back to the JVM’s default SSL engine if not available. However, if set to true, the server will fail to start at all in this case.
HONO_KURA_PORT
hono.kura.port
no 8883 The secure port that the protocol adapter should listen on.
See Port Configuration below for details.
HONO_KURA_SECUREPROTOCOLS
hono.kura.secureProtocols
no TLSv1.3,TLSv1.2 A (comma separated) list of secure protocols (in order of preference) that are supported when negotiating TLS sessions. Please refer to the vert.x documentation for a list of supported protocol names.
HONO_AMQP_SUPPORTEDCIPHERSUITES
hono.amqp.supportedCipherSuites
no - A (comma separated) list of names of cipher suites (in order of preference) that the adapter may use in TLS sessions with devices. Please refer to JSSE Cipher Suite Names for a list of supported names.
HONO_KURA_TENANTIDLETIMEOUT
hono.kura.tenantIdleTimeout
no PT0S The duration after which the protocol adapter removes local state of the tenant (e.g. open AMQP links) with an amount and a unit, e.g. 2h for 2 hours. See the java.time.Duration documentation for an explanation of the format. The leading PT can be omitted if only specifying hours, minutes or seconds. The value 0s (or PT0S) disables the timeout.
HONO_KURA_SENDMESSAGETODEVICETIMEOUT
hono.kura.sendMessageToDeviceTimeout
no 1000 The amount of time (milliseconds) after which the sending of a command to a device using QoS 1 is considered to be failed. The value of this variable should be increased in cases where devices are connected over a network with high latency.

The variables only need to be set if the default values do not match your environment.

In addition to the options described in the table above, this component supports the following standard configuration options:

Port Configuration

The Kura protocol adapter can be configured to listen for connections on

  • a secure port only (default) or
  • an insecure port only or
  • both a secure and an insecure port (dual port configuration)

The Kura protocol adapter will fail to start if none of the ports is configured properly.

Secure Port Only

The protocol adapter needs to be configured with a private key and certificate in order to open a TLS secured port.

There are two alternative ways for doing so:

  1. either setting the HONO_KURA_KEYSTOREPATH and the HONO_KURA_KEYSTOREPASSWORD variables in order to load the key & certificate from a password protected key store, or
  2. setting the HONO_KURA_KEYPATH and HONO_KURA_CERTPATH variables in order to load the key and certificate from two separate PEM files in PKCS8 format.

When starting up, the protocol adapter will bind a TLS secured socket to the default secure MQTT port 8883. The port number can also be set explicitly using the HONO_KURA_PORT variable.

The HONO_KURA_BINDADDRESS variable can be used to specify the network interface that the port should be exposed on. By default the port is bound to the loopback device only, i.e. the port will only be accessible from the local host. Setting this variable to 0.0.0.0 will let the port being bound to all network interfaces (be careful not to expose the port unintentionally to the outside world).

Insecure Port Only

The secure port will mostly be required for production scenarios. However, it might be desirable to expose a non-TLS secured port instead, e.g. for testing purposes. In any case, the non-secure port needs to be explicitly enabled either by

  • explicitly setting HONO_KURA_INSECUREPORT to a valid port number, or by
  • implicitly configuring the default MQTT port (1883) by simply setting HONO_KURA_INSECUREPORTENABLED to true.

The protocol adapter issues a warning on the console if HONO_KURA_INSECUREPORT is set to the default secure MQTT port (8883).

The HONO_KURA_INSECUREPORTBINDADDRESS variable can be used to specify the network interface that the port should be exposed on. By default the port is bound to the loopback device only, i.e. the port will only be accessible from the local host. This variable might be used to e.g. expose the non-TLS secured port on a local interface only, thus providing easy access from within the local network, while still requiring encrypted communication when accessed from the outside over public network infrastructure.

Setting this variable to 0.0.0.0 will let the port being bound to all network interfaces (be careful not to expose the port unintentionally to the outside world).

Dual Port

The protocol adapter may be configured to open both a secure and a non-secure port at the same time simply by configuring both ports as described above. For this to work, both ports must be configured to use different port numbers, otherwise startup will fail.

Ephemeral Ports

Both the secure as well as the insecure port numbers may be explicitly set to 0. The protocol adapter will then use arbitrary (unused) port numbers determined by the operating system during startup.