# Apache Kafka - Publish message action
The Publish message action publishes a new message to a selected Kafka topic. You can select schemas in AVRO or Protobuf format for the Kafka message body and message key.
For publishing multiple messages in a single batch operation, use the Publish messages action (batch).
MESSAGE SIZE LIMITATION
The maximum message size is 50 MB.
# Input
| Input field | Description |
|---|---|
| Topic | Select or enter the name of the topic where you plan to publish a message. |
| Message schema source | Define your message schema source. Options include:
|
| Message schema | Select the message schema based on the Message schema source selection. |
| Protobuf message schema | Select the Protobuf message schema from the schema registry. This field appears when Common data model – Protobuf is selected as the message schema source. |
| Key schema type | Configure the schema type for your message keys. Options include:
|
| Key schema | Select the key schema from your available schemas. This field appears when Schema registry is selected as the key schema type. |
| Partition | Specify a topic partition (index starts from 0) to explicitly publish to. If not specified, Kafka selects the partition automatically. |
| Message | Provide the message content. |
| Key | Provide the message key to be stored with the message. |
| Message headers | Provide a list of key-value pairs to be stored with the message as headers. Header keys may be duplicated. |
| Key (Message headers) | Enter the header key name. |
| Value (Message headers) | Enter the header value. |
# Output
The output contains useful information after a successful action. To use the output in downstream steps, map in the relevant datapill.
| Output field | Description |
|---|---|
| Size | Size of the published message. |
| Timestamp | Timestamp of the published message. |
| Partition | Partition ID where the message was added. |
| Offset | The message offset, which is a unique message identifier in Kafka. |
Last updated: 2/19/2026, 7:42:12 PM