Semantic Conventions for Messaging Spans

Status: Experimental

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 until a transition plan to the (future) stable semantic conventions has been published. Conventions include, but are not limited to, attributes, metric and span names, and unit of measure.

Definitions

Message

Although messaging systems are not as standardized as, e.g., HTTP, it is assumed that the following definitions are applicable to most of them that have similar concepts at all (names borrowed mostly from JMS):

A message is an envelope with a potentially empty body. This envelope may offer the possibility to convey additional metadata, often in key/value form.

A message is sent by a message producer to:

• Physically: some message broker (which can be e.g., a single server, or a cluster, or a local process reached via IPC). The broker handles the actual delivery, re-delivery, persistence, etc. In some messaging systems the broker may be identical or co-located with (some) message consumers. With Apache Kafka, the physical broker a message is written to depends on the number of partitions, and which broker is the leader of the partition the record is written to.
• Logically: some particular message destination.

Messages can be delivered to 0, 1, or multiple consumers depending on the dispatching semantic of the protocol.

Producer

The “producer” is a specific instance, process or device that creates and publishes a message. “Publishing” is the process of sending a message or batch of messages to the intermediary or consumer.

Consumer

A “consumer” receives the message and acts upon it. It uses the context and data to execute some logic, which might lead to the occurrence of new events.

The consumer receives, processes, and settles a message. “Receiving” is the process of obtaining a message from the intermediary, “processing” is the process of acting on the information a message contains, “settling” is the process of notifying an intermediary that a message was processed successfully.

Intermediary

An “intermediary” receives a message to forward it to the next receiver, which might be another intermediary or a consumer.

Destinations

A destination represents the entity within a messaging system where messages are published to and consumed from.

A destination is usually uniquely identified by its name within the messaging system instance. Examples of a destination name would be an URL or a simple one-word identifier.

In some use cases, messages are routed within one or multiple brokers. In such cases, the destination the message was originally published to is different from the destination it is being consumed from. When information about the destination where the message was originally published to is available, consumers can record them under the destination_publish namespace.

Typical examples of destinations include Kafka topics, RabbitMQ queues and topics.

Message consumption

The consumption of a message can happen in multiple steps. First, the lower-level receiving of a message at a consumer, and then the logical processing of the message. Often, the waiting for a message is not particularly interesting and hidden away in a framework that only invokes some handler function to process a message once one is received (in the same way that the listening on a TCP port for an incoming HTTP message is not particularly interesting).

Conversations

In some messaging systems, a message can receive one or more reply messages that answers a particular other message that was sent earlier. All messages that are grouped together by such a reply-relationship are called a conversation. The grouping usually happens through some sort of “In-Reply-To:” meta information or an explicit conversation ID (sometimes called correlation ID). Sometimes a conversation can span multiple message destinations (e.g. initiated via a topic, continued on a temporary one-to-one queue).

Temporary and anonymous destinations

Some messaging systems support the concept of temporary destination (often only temporary queues) that are established just for a particular set of communication partners (often one to one) or conversation. Often such destinations are also unnamed (anonymous) or have an auto-generated name.

Conventions

Given these definitions, the remainder of this section describes the semantic conventions for Spans describing interactions with messaging systems.

Context propagation

A message may traverse many different components and layers in one or more intermediaries when it is propagated from the producer to the consumer(s). To be able to correlate consumer traces with producer traces using the existing context propagation mechanisms, all components must propagate context down the chain.

Messaging systems themselves may trace messages as the messages travels from producers to consumers. Such tracing would cover the transport layer but would not help in correlating producers with consumers. To be able to directly correlate producers with consumers, another context that is propagated with the message is required.

A message creation context allows correlating producers with consumers of a message and model the dependencies between them, regardless of the underlying messaging transport mechanism and its instrumentation.

The message creation context is created by the producer and should be propagated to the consumer(s). Consumer traces cannot be directly correlated with producer traces if the message creation context is not attached and propagated with the message.

A producer SHOULD attach a message creation context to each message. If possible, the message creation context SHOULD be attached in such a way that it cannot be changed by intermediaries.

This document does not specify the exact mechanisms on how the creation context is attached/extracted to/from messages. Future versions of these conventions will give clear recommendations, following industry standards including, but not limited to Trace Context: AMQP protocol and Trace Context: MQTT protocol once those standards reach a stable state.

Span name

The span name SHOULD be set to the message destination name and the operation being performed in the following format:

<destination name> <operation name>

The destination name SHOULD only be used for the span name if it is known to be of low cardinality (cf. general span name guidelines). This can be assumed if it is statically derived from application code or configuration. Wherever possible, the real destination names after resolving logical or aliased names SHOULD be used. If the destination name is dynamic, such as a conversation ID or a value obtained from a Reply-To header, it SHOULD NOT be used for the span name. In these cases, an artificial destination name that best expresses the destination, or a generic, static fallback like "(anonymous)" for anonymous destinations SHOULD be used instead.

The values allowed for <operation name> are defined in the section Operation names below.

Examples:

• shop.orders publish
• shop.orders receive
• shop.orders settle
• print_jobs publish
• topic with spaces process
• AuthenticationRequest-Conversations settle
• (anonymous) publish ((anonymous) being a stable identifier for an unnamed destination)

Messaging system specific adaptions to span naming MUST be documented in semantic conventions for specific messaging technologies.

Operation names

The following operations related to messages are defined for these semantic conventions:

Span kind

Span kinds SHOULD be set according to the following table, based on the operation a span describes.

For cases not covered by the table above, the span kind should be set according to the generic specification about span kinds, e. g. it should be set to CLIENT for the “Publish” span if its context is not used as creation context and if the “Publish” span models a synchronous call to the intermediary.

Setting span kinds according to this table ensures that span links between consumers and producers always exist between a PRODUCER span on the producer side and a CONSUMER span on the consumer side. This allows analysis tools to interpret linked traces without the need for additional semantic hints.

Trace structure

Producer spans

“Create” spans MAY be created when a message is created or passed to the client library or other component responsible for publishing. A single “Create” span SHOULD account only for a single message. “Publish” spans SHOULD be created for operations of sending or publishing a message to an intermediary. A single “Publish” span can account for a single message, or for multiple messages (in the case of sending messages in batches).

If a user provides a custom creation context in a message, this context SHOULD NOT be modified and a “Create” span SHOULD NOT be created. Otherwise, if a “Create” span exists for a message, its context SHOULD be injected into the message. If no “Create” span exists and no custom creation context is injected into the message, the context of the related “Publish” span SHOULD be injected into the message.

The “Publish” span SHOULD always link to the creation context that was injected into a message either from a “Create” span or as a custom creation context.

Consumer spans

“Receive” spans SHOULD be created for operations of passing messages to the application when those operations are initiated by the application code (pull-based scenarios).

“Process” spans SHOULD be created for operations of passing messages to the application when those operations are not initiated by the application code (push-based scenarios). Such “Process” span covers the duration of such an operation, which is usually a callback or handler.

“Process” spans MAY be created in addition to “Receive” spans for pull-based scenarios for operations of processing messages. Such spans could be created by application code, or by abstraction layers built on top of messaging SDKs.

“Receive” or “Process” spans MUST NOT be created for messages that are pre-fetched or cached by messaging libraries or SDKs until they are forwarded to the caller.

A single “Process” or “Receive” span can account for a single message, for a batch of messages, or for no message at all (if it is signalled that no messages were received). For each message it accounts for, the “Process” or “Receive” span SHOULD link to the message’s creation context.

“Settle” spans SHOULD be created for every manually or automatically triggered settlement operation. A single “Settle” span can account for a single message or for multiple messages (in case messages are passed for settling as batches). For each message it accounts for, the “Settle” span MAY link to the creation context of the message.

Messaging attributes

Messaging attributes are organized into the following namespaces:

• messaging.message: Contains per-message attributes that describe individual messages. Those attributes are relevant only for spans or links that represent a single message.
• messaging.destination: Contains attributes that describe the logical entity messages are published to. See Destinations for more details.
• messaging.destination_publish: Contains attributes that describe the logical entity messages were originally published to. See Destinations for more details.
• messaging.batch: Contains attributes that describe batch operations.
• messaging.consumer: Contains consumer attributes that describe the application instance that consumes a message. See consumer for more details.

Messaging system-specific attributes MUST be defined in the corresponding messaging.{system} namespace as described in Attributes specific to certain messaging systems.

Attribute	Type	Description	Examples	Requirement Level	Stability
messaging.operation	string	A string identifying the kind of messaging operation. [1]	publish	Required
messaging.system	string	An identifier for the messaging system being used. See below for a list of well-known identifiers.	activemq	Required
error.type	string	Describes a class of error the operation ended with. [2]	amqp:decode-error; KAFKA_STORAGE_ERROR; channel-error	Conditionally Required [3]
messaging.batch.message_count	int	The number of messages sent, received, or processed in the scope of the batching operation. [4]	0; 1; 2	Conditionally Required [5]
messaging.destination.anonymous	boolean	A boolean that is true if the message destination is anonymous (could be unnamed or have auto-generated name).		Conditionally Required [6]
messaging.destination.name	string	The message destination name [7]	MyQueue; MyTopic	Conditionally Required [8]
messaging.destination.template	string	Low cardinality representation of the messaging destination name [9]	/customers/{customerId}	Conditionally Required [10]
messaging.destination.temporary	boolean	A boolean that is true if the message destination is temporary and might not exist anymore after messages are processed.		Conditionally Required [11]
server.address	string	Server domain name if available without reverse DNS lookup; otherwise, IP address or Unix domain socket name. [12]	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 If a client id is available
messaging.destination.partition.id	string	The identifier of the partition messages are sent to or received from, unique within the messaging.destination.name.	1	Recommended When applicable.
messaging.message.body.size	int	The size of the message body in bytes. [13]	1439	Recommended
messaging.message.conversation_id	string	The conversation ID identifying the conversation to which the message belongs, represented as a string. Sometimes called “Correlation ID”.	MyConversationId	Recommended
messaging.message.envelope.size	int	The size of the message body and metadata in bytes. [14]	2738	Recommended
messaging.message.id	string	A value used by the messaging system as an identifier for the message, represented as a string.	452a7c7c7c7048c2f887f61572b18fc2	Recommended
network.peer.address	string	Peer address of the messaging intermediary node where the operation was performed. [15]	10.1.2.80; /tmp/my.sock	Recommended If applicable for this messaging system.
network.peer.port	int	Peer port of the messaging intermediary node where the operation was performed.	65123	Recommended if and only if network.peer.address is set.
server.port	int	Server port number. [16]	80; 8080; 443	Recommended

[1]: If a custom value is used, it MUST be of low cardinality.

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

[3]: If and only if the messaging operation has failed.

[4]: 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.

[5]: If the span describes an operation on a batch of messages.

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

[7]: 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.

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

[9]: Destination names could be constructed from templates. An example would be a destination name involving a user name or product id. Although the destination name in this case is of high cardinality, the underlying template is of low cardinality and can be effectively used for grouping and aggregation.

[10]: If available. Instrumentations MUST NOT use messaging.destination.name as template unless low-cardinality of destination name is guaranteed.

[11]: If value is true. When missing, the value is assumed to be false.

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

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

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

[15]: Semantic conventions for individual messaging systems SHOULD document whether network.peer.* attributes are applicable. Network peer address and port are important when the application interacts with individual intermediary nodes directly, If a messaging operation involved multiple network calls (for example retries), the address of the last contacted node SHOULD be used.

[16]: 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.

messaging.operation 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
publish	One or more messages are provided for publishing to an intermediary. If a single message is published, the context of the “Publish” span can be used as the creation context and no “Create” span needs to be created.
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 publishing scenarios.
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.
process	One or more messages are delivered to or processed by a consumer.
settle	One or more messages are settled.

messaging.system 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
activemq	Apache ActiveMQ
aws_sqs	Amazon Simple Queue Service (SQS)
eventgrid	Azure Event Grid
eventhubs	Azure Event Hubs
servicebus	Azure Service Bus
gcp_pubsub	Google Cloud Pub/Sub
jms	Java Message Service
kafka	Apache Kafka
rabbitmq	RabbitMQ
rocketmq	Apache RocketMQ

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.

Consumer attributes

The following additional attributes describe message consumer operations.

Since messages could be routed by brokers, the destination messages are published to may not match with the destination they are consumed from.

If information about the original destination is available on the consumer, consumer instrumentations SHOULD populate the attributes under the namespace messaging.destination_publish.*

Attribute	Type	Description	Examples	Requirement Level	Stability
messaging.destination_publish.anonymous	boolean	A boolean that is true if the publish message destination is anonymous (could be unnamed or have auto-generated name).		Recommended
messaging.destination_publish.name	string	The name of the original destination the message was published to [1]	MyQueue; MyTopic	Recommended

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

Per-message attributes

All messaging operations (publish, receive, process, or others not covered by this specification) can describe both single and/or batch of messages. Attributes in the messaging.message or messaging.{system}.message namespace describe individual messages. For single-message operations they SHOULD be set on corresponding span.

For batch operations, per-message attributes are usually different and cannot be set on the corresponding span. In such cases the attributes SHOULD be set on links. See Batch receiving for more information on correlation using links.

Some messaging systems (e.g., Kafka, Azure EventGrid) allow publishing a single batch of messages to different topics. In such cases, the attributes in messaging.destination MAY be set on links. Instrumentations MAY set destination attributes on the span if all messages in the batch share the same destination.

Attributes specific to certain messaging systems

All attributes that are specific for a messaging system SHOULD be populated in messaging.{system} namespace. Attributes that describe a message, a destination, a consumer, or a batch of messages SHOULD be populated under the corresponding namespace:

• messaging.{system}.message.*: Describes attributes for individual messages
• messaging.{system}.destination.*: Describes the destination a message (or a batch) are published to and received from respectively. The combination of attributes in these namespaces should uniquely identify the entity and include properties significant for this messaging system. For example, Kafka instrumentations should include partition identifier.
• messaging.{system}.consumer.*: Describes message consumer properties
• messaging.{system}.batch.*: Describes message batch properties

Examples

This section contains a list of examples illustrating the use of the conventions outlined above. Green boxes denote spans that are required to exist in order to conform to those conventions. Other boxes denote spans that are not required and covered by the conventions, but are hopefully helpful in understanding how messaging spans can be integrated into an overall trace flow. Solid arrows denote parent/child relationships, dotted arrows denote link relationships.

Topic with multiple consumers

Given is a publisher that publishes a message to a topic exchange “T” on RabbitMQ, and two consumers which both get the message delivered.

flowchart LR;
  subgraph PRODUCER
  direction TB
  P[Span Publish A]
  end
  subgraph CONSUMER1
  direction TB
  R1[Span Process A 1]
  end
  subgraph CONSUMER2
  direction TB
  R2[Span Process A 2]
  end
  P-. link .-R1;
  P-. link .-R2;

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

Batch receiving

Given is a publisher that publishes two messages to a topic “Q” on Kafka, and a consumer which receives both messages in one batch.

flowchart LR;
  subgraph PRODUCER
  direction TB
  PA[Span Publish A]
  PB[Span Publish B]
  end
  subgraph CONSUMER1
  direction TB
  D1[Span Receive A B]
  end
  PA-. link .-D1;
  PB-. link .-D1;

  classDef normal fill:green
  class PA,PB,D1 normal
  linkStyle 0,1 color:green,stroke:green

Batch publishing

Given is a publisher that publishes a batch with two messages to a topic “Q” on Kafka, and two different consumers receiving one of the messages.

flowchart LR;
  subgraph PRODUCER
  direction TB
  CA[Span Create A]
  CB[Span Create B]
  P[Span Publish]
  end
  subgraph CONSUMER1
  direction TB
  D1[Span Receive A]
  end
  subgraph CONSUMER2
  direction TB
  D2[Span Receive B]
  end
  CA-. link .-P;
  CB-. link .-P;
  CA-. link .-D1;
  CB-. link .-D2;

  classDef normal fill:green
  class P,CA,CB,D1,D2 normal
  linkStyle 0,1,2,3 color:green,stroke:green

Semantic Conventions for specific messaging technologies

More specific Semantic Conventions are defined for the following messaging technologies:

• Kafka: Semantic Conventions for Apache Kafka.
• RabbitMQ: Semantic Conventions for RabbitMQ.
• RocketMQ: Semantic Conventions for Apache RocketMQ.