Semantic Conventions for Google Cloud Pub/Sub

Status: Experimental

The Semantic Conventions for Google Cloud Pub/Sub 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 "gcp_pubsub" and SHOULD be provided at span creation time.

Span attributes

For Google Cloud Pub/Sub, 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. [1]	ack; nack; send	Required
error.type	string	Describes a class of error the operation ended with. [2]	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. [3]	0; 1; 2	Conditionally Required [4]
messaging.destination.name	string	The message destination name [5]	MyQueue; MyTopic	Conditionally Required [6]
messaging.gcp_pubsub.message.ordering_key	string	The ordering key for a given message. If the attribute is not present, the message does not have an ordering key.	ordering_key	Conditionally Required If the message type has an ordering key set.
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.destination.subscription.name	string	Google Pub/Sub subscription name.	subscription-a	Recommended
messaging.gcp_pubsub.message.ack_deadline	int	The ack deadline in seconds set for the modify ack deadline request.	10	Recommended
messaging.gcp_pubsub.message.ack_id	string	The ack id for a given message.	ack_id	Recommended
messaging.gcp_pubsub.message.delivery_attempt	int	The delivery attempt for a given message.	2	Recommended
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. [9]	80; 8080; 443	Recommended

[1] messaging.operation.name: The messaging.operation.name has the following list of well-known values in the context of Google Pub/Sub. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

• ack and nack for settlement operations
• send for publishing operations
• modack for extending the lease for a single message or batch of messages
• subscribe for operations that represent the time from after the message was received to when the message is acknowledged, negatively acknowledged, or expired.
• create and receive for common messaging operations

[2] 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.

[3] 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.

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

[5] 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.

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

[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] 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.

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

• messaging.destination.name
• messaging.destination.subscription.name
• 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.

Examples

Asynchronous Batch Publish Example

Given is a process P that asynchronously publishes 2 messages in a batch to a topic T on Pub/Sub.

flowchart LR;
  subgraph PRODUCER
  direction LR
  CA[Span Create A]
  CB[Span Create B]
  P[Span Send A B]
  end
  CA-. link .-P;
  CB-. link .-P;

  classDef producer fill:green
  class P,CA,CB producer
  classDef normal fill:green
  class PA,PB,D1 normal
  linkStyle 0,1 color:green,stroke:green

Unary Pull Example

flowchart TD;
  subgraph CONSUMER
  direction LR
  R1[Receive A]
  SM1[Ack A]
  EM1[Modack A]
  end
  subgraph PRODUCER
  direction LR
  CM1[Create A]
  PM1[Send]
  end
  %% Link 0
  CM1-. link .-PM1;
  %% Link 1
  CM1-. link .-R1;
  %% Link 2
  R1-. link .-SM1;
  %% Link 3
  R1-. link .-EM1;

  %% Style the node and corresponding link
  %% Producer links and nodes
  classDef producer fill:green
  class PM1,CM1 producer
  linkStyle 0 color:green,stroke:green

  %% Consumer links and nodes
  classDef consumer fill:#49fcdc
  class R1 consumer
  linkStyle 1 color:#49fcdc,stroke:#49fcdc

  classDef ack fill:#577eb5
  class SM1 ack
  linkStyle 2 color:#577eb5,stroke:#577eb5

  classDef modack fill:#0560f2
  class EM1 modack
  linkStyle 3 color:#0560f2,stroke:#0560f2