Semantic Conventions for Kafka

Status: Experimental

The Semantic Conventions for Apache Kafka extend and override the Messaging Semantic Conventions.

[!Warning]

Existing messaging instrumentations that are using v1.24.0 of this document (or prior):

• SHOULD NOT change the version of the messaging conventions that they emit by default until the messaging semantic conventions are marked stable. Conventions include, but are not limited to, attributes, metric and span names, span kind and unit of measure.
• SHOULD introduce an environment variable OTEL_SEMCONV_STABILITY_OPT_IN in the existing major version which is a comma-separated list of values. The list of values includes:
  • messaging - emit the new, stable messaging conventions, and stop emitting the old experimental messaging conventions that the instrumentation emitted previously.
  • messaging/dup - emit both the old and the stable messaging conventions, allowing for a seamless transition.
  • The default behavior (in the absence of one of these values) is to continue emitting whatever version of the old experimental messaging conventions the instrumentation was emitting previously.
  • Note: messaging/dup has higher precedence than messaging in case both values are present
• SHOULD maintain (security patching at a minimum) the existing major version for at least six months after it starts emitting both sets of conventions.
• SHOULD drop the environment variable in the next major version.
• SHOULD emit the new, stable values for span name, span kind and similar “single” valued concepts when messaging/dup is present in the list.

messaging.system MUST be set to "kafka" and SHOULD be provided at span creation time.

Span attributes

For Apache Kafka, the following additional attributes are defined:

Attribute	Type	Description	Examples	Requirement Level	Stability
messaging.operation.name	string	The system-specific name of the messaging operation.	ack; nack; send	Required
error.type	string	Describes a class of error the operation ended with. [1]	amqp:decode-error; KAFKA_STORAGE_ERROR; channel-error	Conditionally Required If and only if the messaging operation has failed.
messaging.batch.message_count	int	The number of messages sent, received, or processed in the scope of the batching operation. [2]	0; 1; 2	Conditionally Required [3]
messaging.destination.name	string	The message destination name [4]	MyQueue; MyTopic	Conditionally Required [5]
messaging.kafka.message.tombstone	boolean	A boolean that is true if the message is a tombstone.		Conditionally Required [6]
messaging.operation.type	string	A string identifying the type of the messaging operation. [7]	create; send; receive	Conditionally Required If applicable.
server.address	string	Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [8]	example.com; 10.1.2.80; /tmp/my.sock	Conditionally Required If available.
messaging.client.id	string	A unique identifier for the client that consumes or produces a message.	client-5; myhost@8742@s8083jm	Recommended
messaging.consumer.group.name	string	Kafka consumer group id.	my-group; indexer	Recommended
messaging.destination.partition.id	string	String representation of the partition id the message (or batch) is sent to or received from.	1	Recommended
messaging.kafka.message.key	string	Message keys in Kafka are used for grouping alike messages to ensure they’re processed on the same partition. They differ from messaging.message.id in that they’re not unique. If the key is null, the attribute MUST NOT be set. [9]	myKey	Recommended If span describes operation on a single message.
messaging.kafka.offset	int	The offset of a record in the corresponding Kafka partition.	42	Recommended If span describes operation on a single message.
messaging.message.id	string	A value used by the messaging system as an identifier for the message, represented as a string.	452a7c7c7c7048c2f887f61572b18fc2	Recommended If span describes operation on a single message.
server.port	int	Server port number. [10]	80; 8080; 443	Recommended
messaging.message.body.size	int	The size of the message body in bytes. Only applicable for spans describing single message operations. [11]	1439	Opt-In

[1] error.type: The error.type SHOULD be predictable, and SHOULD have low cardinality.

When error.type is set to a type (e.g., an exception type), its canonical class name identifying the type within the artifact SHOULD be used.

Instrumentations SHOULD document the list of errors they report.

The cardinality of error.type within one instrumentation library SHOULD be low. Telemetry consumers that aggregate data from multiple instrumentation libraries and applications should be prepared for error.type to have high cardinality at query time when no additional filters are applied.

If the operation has completed successfully, instrumentations SHOULD NOT set error.type.

If a specific domain defines its own set of error identifiers (such as HTTP or gRPC status codes), it’s RECOMMENDED to:

• Use a domain-specific attribute
• Set error.type to capture all errors, regardless of whether they are defined within the domain-specific set or not.

[2] messaging.batch.message_count: Instrumentations SHOULD NOT set messaging.batch.message_count on spans that operate with a single message. When a messaging client library supports both batch and single-message API for the same operation, instrumentations SHOULD use messaging.batch.message_count for batching APIs and SHOULD NOT use it for single-message APIs.

[3] messaging.batch.message_count: If the span describes an operation on a batch of messages.

[4] messaging.destination.name: Destination name SHOULD uniquely identify a specific queue, topic or other entity within the broker. If the broker doesn’t have such notion, the destination name SHOULD uniquely identify the broker.

[5] messaging.destination.name: If span describes operation on a single message or if the value applies to all messages in the batch.

[6] messaging.kafka.message.tombstone: If value is true. When missing, the value is assumed to be false.

[7] messaging.operation.type: If a custom value is used, it MUST be of low cardinality.

[8] server.address: Server domain name of the broker if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name.

[9] messaging.kafka.message.key: If the key type is not string, it’s string representation has to be supplied for the attribute. If the key has no unambiguous, canonical string form, don’t include its value.

[10] server.port: When observed from the client side, and when communicating through an intermediary, server.port SHOULD represent the server port behind any intermediaries, for example proxies, if it’s available.

[11] messaging.message.body.size: This can refer to both the compressed or uncompressed body size. If both sizes are known, the uncompressed body size should be used.

The following attributes can be important for making sampling decisions and SHOULD be provided at span creation time (if provided at all):

• messaging.consumer.group.name
• messaging.destination.name
• messaging.destination.partition.id
• messaging.operation.name
• messaging.operation.type
• server.address
• server.port

error.type has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

Value	Description	Stability
_OTHER	A fallback error value to be used when the instrumentation doesn’t define a custom value.

messaging.operation.type has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

Value	Description	Stability
create	A message is created. “Create” spans always refer to a single message and are used to provide a unique creation context for messages in batch sending scenarios.
process	One or more messages are processed by a consumer.
receive	One or more messages are requested by a consumer. This operation refers to pull-based scenarios, where consumers explicitly call methods of messaging SDKs to receive messages.
send	One or more messages are provided for sending to an intermediary. If a single message is sent, the context of the “Send” span can be used as the creation context and no “Create” span needs to be created.
settle	One or more messages are settled.

For Apache Kafka producers, peer.service SHOULD be set to the name of the broker or service the message will be sent to. The service.name of a Consumer’s Resource SHOULD match the peer.service of the Producer, when the message is directly passed to another service. If an intermediary broker is present, service.name and peer.service will not be the same.

messaging.client.id SHOULD be set to the client name of a consumer or producer, which is unique for each individual instance.

Examples

Apache Kafka with Quarkus or Spring Boot Example

In this example, the producer publishes a message to a topic T on Apache Kafka. Consumer receives the message, processes it and commits the offset.

Frameworks such as Quarkus and Spring Boot provide integrations with Kafka allowing to configure and instrument processing callbacks, so corresponding instrumentations should create “Process” spans in addition to “Receive” spans created by Kafka instrumentations for polling calls.

flowchart LR;
  subgraph PRODUCER
  P[Span Send]
  end
  subgraph CONSUMER
  direction TB
  R1[Span Poll]
  R2[Span Process]
  R3[Span Commit]
  end

  P-. link .-R1;
  P-. link .-R2;
  R2-- parent ---R3;

  classDef normal fill:green
  class P,R1,R2,R3 normal
  linkStyle 0 color:green,stroke:green
  linkStyle 1 color:green,stroke:green