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Pentaho Documentation

MQTT Consumer

Parent article

The PDI client can pull streaming data from an MQTT broker or clients through an MQTT transformation. The parent MQTT Consumer step runs a child transformation that executes according to the message batch size or duration, allowing you to process a continuous stream of records in near real-time. The child transformation must start with the Get records from stream step.

Additionally, from the MQTT Consumer step, you can select a step in the child transformation to stream records back to the parent transformation. This capability allows records processed by an MQTT Consumer step in a parent transformation to be passed downstream to any other steps included within the same parent transformation.

AEL considerations

When using the MQTT Consumer step with the Adaptive Execution Layer (AEL), the following factors affect performance and results:

  • If your MQTT is configured to accept SSL connections, you will need to adjust the AEL daemon application.properties file for SSL keystore. For more information, see Using MQTT with SSL on AEL.
  • When using the MQTT Consumer step with AEL, you must execute the child transformation according to Duration (ms) only. Specify the duration length on the Batch tab.

General

The MQTT Consumer step requires Setup, Security, Batch, Fields, Result fields, and Options definitions to stream messages.

MQTT Consumer dialog box

Enter the following information for the Step Name and Transformation fields:

OptionDescription
Step nameSpecifies the unique name of the step on the canvas. The Step name is set to MQTT Consumer’by default.
Transformation

Specify the child transformation to execute by performing any of the following actions:

If you select a transformation that has the same root path as the current transformation, the variable ${Internal.Entry.Current.Directory} is automatically inserted in place of the common root path. For example, if the current transformation's path is: /home/admin/transformation.ktr and you select a transformation in the directory /home/admin/path/sub.ktr, then the path is automatically converted to: ${Internal.Entry.Current.Directory}/path/sub.ktr

If you are working with a repository, you must specify the name of the transformation. If you are not working with a repository, you must specify the XML file name of the transformation.

Transformations previously specified by reference are automatically converted to be specified by the transformation name in the Pentaho Repository.

NoteThe selected child transformation must start with the Get Records from Stream step.

Create and save a new child transformation

If you do not already have a child transformation, you can create one while setting up the MQTT Consumer step. When you click the New button, a new child transformation will automatically generate the required Get Records from Stream step in a new canvas tab. All your fields and types are customized in the child transformation's Get Records from Stream step to match the fields and types specified in the Fields tab of the parent MQTT Consumer step.

Procedure

  1. In the MQTT Consumer step, click New. The Save As dialog box appears.

  2. Navigate to the location where you want to save your new child transformation, then type in the file name.

  3. Click Save.

    A notification box displays informing you that the child transformation has been created and opened in a new tab. If you do not want to see this notification in the future, select the Don't show me this again check box.
  4. Click the new transformation tab to view and edit the child transformation.

    It automatically contains the Get Records from Stream step. (Optional) You can continue to build this transformation and save it.
  5. When finished, return to the MQTT Consumer step.

Options

The MQTT Consumer step includes several tabs. Each tab is described below.

Setup tab

Setup tab in MQTT Consumer

In the Setup tab, define the connections used for receiving messages, topics to which you want to subscribe, and the consumer group for the topics.

OptionDescription
ConnectionSpecify the address of the MQTT server to which this step will connect for sending or retrieving messages.
TopicsSpecify the MQTT topic(s) to be subscribed to.
Quality of Service (QoS)

Quality of Service (QoS) is a level of guarantee for message delivery. Select one of the following options.

  • At most once (0), which is the default value
  • At least once (1)
  • Exactly once (2)

Security tab

Security tab in MQTT Consumer

The Security tab allows you to define authentication credentials for the MQTT server. This tab includes the following options:

OptionDescription
UsernameSpecify the user name required to access the MQTT server.
PasswordSpecify the password associated with the Username.
Use secure protocol

Select this option if you want to define SSL properties for the connection.

This security protocol setting is used only on Kettle. It is not used on AEL Spark.

SSL Properties
  • ssl.contextProvider

    Specify the underlying JSSE provider.

  • ssl.enabledCipherSuites

    Specify which ciphers are enabled. Values are dependent on the provider.

  • ssl.keyManager

    Specify the algorithm that will be used to create a KeyManagerFactory object instead of using the default algorithm available in the platform.

  • ssl.keyStore

    Specify the name of the file that contains the KeyStore object that you want the KeyManager to use.

  • ssl.keyStorePassword

    Specify the password for the KeyStore object that you want the KeyManager to use.

  • ssl.keyStoreProvider

    Specify the identifying name or string for the key store provider.

  • ssl.keyStoreType

    Specify the identifying name or string for the type of key store.

  • ssl.protocol

    Specify the type of SSL protocol to use.

  • ssl.trustManager

    Specify the algorithm that will be used to create a TrustManagerFactory object, instead of using the default algorithm available in the platform.

  • ssl.trustStore

    Specify the name of the file that contains the KeyStore object that you want the TrustManager to use.

  • ssl.trustStorePassword

    Specify the password for the TrustStore object that you want the TrustManager to use.

  • ssl.trustStoreProvider

    Specify the identifier or string for the trust store provider.

  • ssl.trustStoreType

    Specify the type of KeyStore object that you want the TrustManager to use.

Batch tab

Batch tab in MQTT Consumer

Use this tab to designate how many messages to consume before processing. You can specify message count and/or a specific amount of time.

How many messages consumed before processing is defined by either the Duration (ms) or the Number of records option. Messages are consumed when either the specified duration or number of records occur. For example, if Duration (ms) is set to 1000 milliseconds and Number of records is 1000, messages are consumed for processing whenever time intervals of 1000 milliseconds are reached or 1000 records have been received. If you set either option to zero, PDI will ignore that parameter.

You can also specify the maximum number of batches used to collect records at the same time.

OptionDescription
Duration (ms)Specify a time in milliseconds. This value is the amount of time the step will spend collecting records prior to the execution of the transformation.

If this option set to a value of 0, then Number of records triggers consumption. Either the Duration or the Number of records option must contain a value greater than 0 to run the transformation.

NoteYou must set this field if you are using Spark as your processing engine.
Number of recordsSpecify a number. After every ‘X’ number of records, the specified transformation will be executed and these ‘X’ records will be passed to the transformation.

If this option set to a value of 0 then Duration triggers consumption. Either the Duration or the Number of records option must contain a value greater than 0 to run the transformation.

Maximum concurrent batchesSpecify the maximum number of batches used to collect records at the same time. The default value is 1, which indicates a single batch is used for collecting records.

This option should only be used when your consumer step cannot keep pace with the speed at which the data is streaming. Your computing environment must have adequate CPU and memory for this implementation. An error will occur if your environment cannot handle the maximum number of concurrent batches specified.

Fields tab

Fields tab in MQTT Consumer

Use this tab to define the fields in the record format.

OptionDescription
Input Name

The input name is received from the MQTT streams. The following are received by default:

  • message

    The individual message contained in a record.

  • topic

    The category to which records are published.

Output NameThe Output Name can be mapped to subscriber and member requirements.
TypeThis will always be a String. This field applies to the Message and Topic input names.

Result fields tab

Result fields tab in MQTT Consumer

Use this tab to select the step from the child transformation that will stream records back to the parent transformation. This capability allows records processed by an MQTT Consumer step in the parent transformation to be passed downstream to any other steps included within the same parent transformation.

OptionDescription
Return fields from:Select the name of the step (from the child transformation) that will stream fields back to the parent transformation. The data values in these returned fields will be available to any subsequent downstream steps in the parent transformation.

Options tab

Options tab in MQTT Consumer

The Options tab includes the following MQTT-specific parameters:

ParameterDescription
Keep Alive IntervalSpecify a maximum number of interval seconds that is permitted to elapse between the point at which the PDI client finishes transmitting one Control Packet and the point it starts sending the next.
Max InflightSpecify a number for the maximum number of messages to have in process at any given time.
Connection TimeoutSpecify the time, in seconds, to disconnect if a message is not received.
Clean Session

Specify if the broker will store or purge messages for a session. Select one of the following.

  • True

    When set to True, the broker will not store any information for the client. All information from a previous persistent session will be purged.

  • False

    When set to False, the broker will store all subscriptions for the client. When the QoS (Quality of Service) parameter is set to either 1 or 2, all missed messages will be stored. For more information, see the Quality of Service parameter in the Setup tab.

Storage Level

Indicates if messages are stored in memory or on disk.

  • The default (blank) is memory.
  • For disk, enter a valid path.

This setting is used only on Kettle. It is not used on AEL Spark, which uses its own configuration.

Server URIsSpecify the MQTT server’s universal resource identifier (URI).
MQTT VersionSpecify the MQTT protocol version that this step is connecting to.
Automatic Reconnect

Enables the client to attempt an automatic re-connect to the server if it becomes disconnected. Select True or False:

  • True

    Yes, attempt to reconnect to the server.

  • False

    No, do not attempt to reconnect to the server.

Using MQTT with SSL on AEL

Complete the following steps to use the MQTT Consumer step with the Pentaho Adaptive Execution Layer (AEL) when connecting to an SSL-enabled MQTT server.

Procedure

  1. Navigate to the data-integration/adaptive-execution/config directory and open the application.properties file with any text editor.

  2. Add the following parameters.

    1. Add the DriverExtraJavaOptions parameter for the Spark driver application and specify the file path for client.ks and its associated password on the cluster:

      sparkDriverExtraJavaOptions=-Dlog4j.configuration=file:${sparkApp}/classes/log4j.xml -Djavax.net.ssl.trustStore=[filepath to client.ks on the cluster]
      -Djavax.net.ssl.trustStorePassword=password
      
      sparkDriverExtraJavaOptions=-Dlog4j.configuration=file:${sparkApp}/classes/log4j.xml -Djavax.net.ssl.trustStore=/home/cloudera/client.ks
      -Djavax.net.ssl.trustStorePassword=password
      
    2. Add the ExtraJavaOptions parameter for the Spark executors and specify the file path for client.ks and its password on the cluster:

      sparkExecutorExtraJavaOptions=-Djavax.net.ssl.trustStore=[filepath to client.ks on the cluster] 
      -Djavax.net.ssl.trustStorePassword=password
      
    sparkExecutorExtraJavaOptions=-Djavax.net.ssl.trustStore=/home/cloudera/client.ks
    -Djavax.net.ssl.trustStorePassword=password
    
  3. Save and close the file.

  4. Navigate to the data-integration/adaptive-execution folder and run the daemon.sh command from the command line interface.

Metadata injection support

All fields of this step support metadata injection. You can use this step with ETL metadata injection to pass metadata to your transformation at runtime.