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Messaging Systems

Status: Experimental

Warning Existing Messaging instrumentations that are using v1.20.0 of this document (or prior):

  • SHOULD NOT change the version of the networking attributes that they emit until the HTTP semantic conventions are marked stable (HTTP stabilization will include stabilization of a core set of networking attributes which are also used in Messaging instrumentations).
  • SHOULD introduce an environment variable OTEL_SEMCONV_STABILITY_OPT_IN in the existing major version which is a comma-separated list of values. The only values defined so far are:
    • http - emit the new, stable networking attributes, and stop emitting the old experimental networking attributes that the instrumentation emitted previously.
    • http/dup - emit both the old and the stable networking attributes, 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 networking attributes the instrumentation was emitting previously.
  • SHOULD maintain (security patching at a minimum) the existing major version for at least six months after it starts emitting both sets of attributes.
  • SHOULD drop the environment variable in the next major version (stable next major version SHOULD NOT be released prior to October 1, 2023).

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 payload. 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.

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. If the format above is used, the operation name MUST match the messaging.operation attribute defined for message consumer spans below.

Examples:

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

Span kind

A producer of a message should set the span kind to PRODUCER unless it synchronously waits for a response: then it should use CLIENT. The processor of the message should set the kind to CONSUMER, unless it always sends back a reply that is directed to the producer of the message (as opposed to e.g., a queue on which the producer happens to listen): then it should use SERVER.

Operation names

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

Operation name Description
publish A message is sent to a destination by a message producer/client.
receive A message is received from a destination by a message consumer/server.
process A message that was previously received from a destination is processed by a message consumer/server.

Messaging attributes

Attribute Type Description Examples Requirement Level
messaging.system string A string identifying the messaging system. kafka; rabbitmq; rocketmq; activemq; AmazonSQS Required
messaging.operation string A string identifying the kind of messaging operation as defined in the Operation names section above. [1] publish Required
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.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.anonymous boolean A boolean that is true if the message destination is anonymous (could be unnamed or have auto-generated name). Conditionally Required: [4]
messaging.destination.name string The message destination name [5] MyQueue; MyTopic Conditionally Required: [6]
messaging.destination.template string Low cardinality representation of the messaging destination name [7] /customers/{customerId} Conditionally Required: [8]
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: [9]
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: [10]
messaging.message.id string A value used by the messaging system as an identifier for the message, represented as a string. 452a7c7c7c7048c2f887f61572b18fc2 Recommended: [11]
messaging.message.payload_compressed_size_bytes int The compressed size of the message payload in bytes. 2048 Recommended: [12]
messaging.message.payload_size_bytes int The (uncompressed) size of the message payload in bytes. Also use this attribute if it is unknown whether the compressed or uncompressed payload size is reported. 2738 Recommended: [13]
network.protocol.name string OSI Application Layer or non-OSI equivalent. The value SHOULD be normalized to lowercase. amqp; mqtt Recommended
network.protocol.version string Version of the application layer protocol used. See note below. [14] 3.1.1 Recommended
network.transport string OSI Transport Layer or Inter-process Communication method. The value SHOULD be normalized to lowercase. tcp; udp Recommended
network.type string OSI Network Layer or non-OSI equivalent. The value SHOULD be normalized to lowercase. ipv4; ipv6 Recommended
server.address string Logical server hostname, matches server FQDN if available, and IP or socket address if FQDN is not known. [15] example.com Conditionally Required: If available.
server.socket.address string Physical server IP address or Unix socket address. If set from the client, should simply use the socket's peer address, and not attempt to find any actual server IP (i.e., if set from client, this may represent some proxy server instead of the logical server). 10.5.3.2 Recommended: If different than server.address.
server.socket.domain string The domain name of an immediate peer. [16] proxy.example.com Recommended: [17]
server.socket.port int Physical server port. 16456 Recommended: If different than server.port.

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

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

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

[5]: Destination name SHOULD uniquely identify a specific queue, topic or other entity within the broker. If the broker does not have such notion, the destination name SHOULD uniquely identify the broker.

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

[7]: 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.

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

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

[10]: Only if span represents operation on a single message.

[11]: Only for spans that represent an operation on a single message.

[12]: Only if span represents operation on a single message.

[13]: Only if span represents operation on a single message.

[14]: network.protocol.version refers to the version of the protocol used and might be different from the protocol client's version. If the HTTP client used has a version of 0.27.2, but sends HTTP version 1.1, this attribute should be set to 1.1.

[15]: This should be the IP/hostname of the broker (or other network-level peer) this specific message is sent to/received from.

[16]: Typically observed from the client side, and represents a proxy or other intermediary domain name.

[17]: If different than server.address and if server.socket.address is set.

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
publish publish
receive receive
process process

Additionally server.port from the network attributes is recommended. Furthermore, it is strongly recommended to add the network.transport attribute and follow its guidelines, especially for in-process queueing systems (like Hangfire, for example). These attributes should be set to the broker to which the message is sent/from which it is received.

Attribute namespaces

  • messaging.message: Contains attributes that describe individual messages
  • messaging.destination: Contains attributes that describe the logical entity messages are published to and received from. See Destinations for more details
  • messaging.batch: Contains attributes that describe batch operations
  • messaging.consumer: Contains attributes that describe application instance that consumes a message. See consumer for more details

Communication with broker is described with general network attributes.

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

Consumer attributes

The receive span is used to track the time used for receiving the message(s), whereas the process span(s) track the time for processing the message(s). Note that one or multiple Spans with messaging.operation = process may often be the children of a Span with messaging.operation = receive. The distinction between receiving and processing of messages is not always of particular interest or sometimes hidden away in a framework (see the Message consumption section above) and therefore the attribute can be left out. For batch receiving and processing (see the Batch receiving and Batch processing examples below) in particular, the attribute SHOULD be set. Even though in that case one might think that the processing span's kind should be INTERNAL, that kind MUST NOT be used. Instead span kind should be set to either CONSUMER or SERVER according to the rules defined above.

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 MAY be set on links. See Batch Receiving and Batch Processing 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

Topic with multiple consumers

Given is a process P, that publishes a message to a topic T on messaging system MS, and two processes CA and CB, which both receive the message and process it.

Process P:  | Span Prod1 |
--
Process CA:              | Span CA1 |
--
Process CB:                 | Span CB1 |
Field or Attribute Span Prod1 Span CA1 Span CB1
Span name "T publish" "T process" "T process"
Parent Span Prod1 Span Prod1
Links
SpanKind PRODUCER CONSUMER CONSUMER
Status Ok Ok Ok
server.address "ms" "ms" "ms"
server.port 1234 1234 1234
messaging.system "rabbitmq" "rabbitmq" "rabbitmq"
messaging.destination.name "T" "T" "T"
messaging.operation "process" "process"
messaging.message.id "a1" "a1" "a1"

Batch receiving

Given is a process P, that publishes two messages to a queue Q on messaging system MS, and a process C, which receives both of them in one batch (Span Recv1) and processes each message separately (Spans Proc1 and Proc2).

Since a span can only have one parent and the propagated trace and span IDs are not known when the receiving span is started, the receiving span will have no parent and the processing spans are correlated with the producing spans using links.

Process P: | Span Prod1 | Span Prod2 |
--
Process C:                      | Span Recv1 |
                                        | Span Proc1 |
                                               | Span Proc2 |
Field or Attribute Span Prod1 Span Prod2 Span Recv1 Span Proc1 Span Proc2
Span name "Q publish" "Q publish" "Q receive" "Q process" "Q process"
Parent Span Recv1 Span Recv1
Links Span Prod1 Span Prod2
SpanKind PRODUCER PRODUCER CONSUMER CONSUMER CONSUMER
Status Ok Ok Ok Ok Ok
server.address "ms" "ms" "ms" "ms" "ms"
server.port 1234 1234 1234 1234 1234
messaging.system "rabbitmq" "rabbitmq" "rabbitmq" "rabbitmq" "rabbitmq"
messaging.destination.name "Q" "Q" "Q" "Q" "Q"
messaging.operation "receive" "process" "process"
messaging.message.id "a1" "a2" "a1" "a2"
messaging.batch.message_count 2

Batch processing

Given is a process P, that publishes two messages to a queue Q on messaging system MS, and a process C, which receives them separately in two different operations (Span Recv1 and Recv2) and processes both messages in one batch (Span Proc1).

Since each span can only have one parent, C3 should not choose a random parent out of C1 and C2, but rather rely on the implicitly selected parent as defined by the tracing API spec. Depending on the implementation, the producing spans might still be available in the meta data of the messages and should be added to C3 as links. The client library or application could also add the receiver span's SpanContext to the data structure it returns for each message. In this case, C3 could also add links to the receiver spans C1 and C2.

The status of the batch processing span is selected by the application. Depending on the semantics of the operation. A span status Ok could, for example, be set only if all messages or if just at least one were properly processed.

Process P: | Span Prod1 | Span Prod2 |
--
Process C:                              | Span Recv1 | Span Recv2 |
                                                                   | Span Proc1 |
Field or Attribute Span Prod1 Span Prod2 Span Recv1 Span Recv2 Span Proc1
Span name "Q publish" "Q publish" "Q receive" "Q receive" "Q process"
Parent Span Prod1 Span Prod2
Links [Span Prod1, Span Prod2 ]
Link attributes Span Prod1: messaging.message.id: "a1"
Span Prod2: messaging.message.id: "a2"
SpanKind PRODUCER PRODUCER CONSUMER CONSUMER CONSUMER
Status Ok Ok Ok Ok Ok
server.address "ms" "ms" "ms" "ms" "ms"
server.port 1234 1234 1234 1234 1234
messaging.system "rabbitmq" "rabbitmq" "rabbitmq" "rabbitmq" "rabbitmq"
messaging.destination.name "Q" "Q" "Q" "Q" "Q"
messaging.operation "receive" "receive" "process"
messaging.message.id "a1" "a2" "a1" "a2"
messaging.batch.message_count 1 1 2

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.