FaaS 的语义约定¶
NOTICE Semantic Conventions are moving to a new location.
No changes to this document are allowed.
Status: Experimental
This document defines how to describe an instance of a function that runs without provisioning or managing of servers (also known as serverless functions or Function as a Service (FaaS)) with spans.
See also the additional instructions for instrumenting AWS Lambda.
- General Attributes
- Function Name
- Difference between invocation and instance
- Incoming Invocations
- Incoming FaaS Span attributes
- Resource attributes as incoming FaaS span attributes
- Outgoing Invocations
- Function Trigger Type
- Datasource
- HTTP
- PubSub
- Timer
- Other
- Example
General Attributes¶
Span name should be set to the function name being executed. Depending on the
value of the faas.trigger attribute, additional attributes MUST be set. For
example, an http trigger SHOULD follow the
HTTP Server semantic conventions.
For more information, refer to the
Function Trigger Type section.
If Spans following this convention are produced, a Resource of type faas MUST
exist following the
Resource semantic convention.
| Attribute | Type | Description | Examples | Requirement Level |
|---|---|---|---|---|
faas.trigger |
string | Type of the trigger which caused this function invocation. [1] | datasource |
Recommended |
faas.invocation_id |
string | The invocation ID of the current function invocation. | af9d5aa4-a685-4c5f-a22b-444f80b3cc28 |
Recommended |
cloud.resource_id |
string | Cloud provider-specific native identifier of the monitored cloud resource (e.g. an ARN on AWS, a fully qualified resource ID on Azure, a full resource name on GCP) [2] | arn:aws:lambda:REGION:ACCOUNT_ID:function:my-function; //run.googleapis.com/projects/PROJECT_ID/locations/LOCATION_ID/services/SERVICE_ID; /subscriptions/<SUBSCIPTION_GUID>/resourceGroups/<RG>/providers/Microsoft.Web/sites/<FUNCAPP>/functions/<FUNC> |
Recommended |
[1]: For the server/consumer span on the incoming side, faas.trigger MUST
be set.
Clients invoking FaaS instances usually cannot set faas.trigger, since they
would typically need to look in the payload to determine the event type. If
clients set it, it should be the same as the trigger that corresponding incoming
would have (i.e., this has nothing to do with the underlying transport used to
make the API call to invoke the lambda, which is often HTTP).
[2]: On some cloud providers, it may not be possible to determine the full
ID at startup, so it may be necessary to set cloud.resource_id as a span
attribute instead.
The exact value to use for cloud.resource_id depends on the cloud provider.
The following well-known definitions MUST be used if you set this attribute and
they apply:
- AWS Lambda: The function ARN. Take care not to use the "invoked ARN" directly but replace any alias suffix with the resolved function version, as the same runtime instance may be invokable with multiple different aliases.
- GCP: The URI of the resource
- Azure: The
Fully Qualified Resource ID
of the invoked function, not the function app, having the form
/subscriptions/<SUBSCIPTION_GUID>/resourceGroups/<RG>/providers/Microsoft.Web/sites/<FUNCAPP>/functions/<FUNC>. This means that a span attribute MUST be used, as an Azure function app can host multiple functions that would usually share a TracerProvider.
faas.trigger MUST be one of the following:
| Value | Description |
|---|---|
datasource |
A response to some data source operation such as a database or filesystem read/write. |
http |
To provide an answer to an inbound HTTP request |
pubsub |
A function is set to be executed when messages are sent to a messaging system. |
timer |
A function is scheduled to be executed regularly. |
other |
If none of the others apply |
Function Name¶
There are 2 locations where the function's name can be recorded: the span name
and the
faas.name Resource attribute.
It is guaranteed that if faas.name attribute is present it will contain the
function name, since it is defined in the semantic convention strictly for that
purpose. It is also highly likely that Span name will contain the function name
(e.g. for Span displaying purposes), but it is not guaranteed (since it is a
weaker "SHOULD" requirement). Consumers that needs such guarantee can use
faas.name attribute as the source.
Difference between invocation and instance¶
For performance reasons (e.g. AWS lambda, or Azure functions), FaaS
providers allocate an execution environment for a single instance of a function
that is used to serve multiple requests. Developers exploit this fact to solve
the cold start issue, caching expensive resource computations between
different function invocations. Furthermore, FaaS providers encourage this
behavior, e.g. Google functions. The faas.instance resource attribute MAY be
set to help correlate function invocations that belong to the same execution
environment. The span attribute faas.invocation_id differs from the resource
attribute faas.instance in the following:
faas.invocation_idrefers to the ID of the current invocation of the function;faas.instancerefers to the execution environment ID of the function.
Incoming Invocations¶
This section describes incoming FaaS invocations as they are reported by the FaaS instance itself.
For incoming FaaS spans, the span kind MUST be Server.
Incoming FaaS Span attributes¶
| Attribute | Type | Description | Examples | Requirement Level |
|---|---|---|---|---|
faas.coldstart |
boolean | A boolean that is true if the serverless function is executed for the first time (aka cold-start). | Recommended | |
faas.trigger |
string | Type of the trigger which caused this function invocation. [1] | datasource |
Required |
[1]: For the server/consumer span on the incoming side, faas.trigger MUST
be set.
Clients invoking FaaS instances usually cannot set faas.trigger, since they
would typically need to look in the payload to determine the event type. If
clients set it, it should be the same as the trigger that corresponding incoming
would have (i.e., this has nothing to do with the underlying transport used to
make the API call to invoke the lambda, which is often HTTP).
Resource attributes as incoming FaaS span attributes¶
In addition to the attributes listed above, any
FaaS or
cloud resource attributes MAY
instead be set as span attributes on incoming FaaS invocation spans: In some
FaaS environments some of the information required for resource attributes is
only readily available in the context of an invocation (e.g. as part of a
"request context" argument) and while a separate API call to look up the
resource information is often possible, it may be prohibitively expensive due to
cold start duration concerns. The cloud.resource_id and cloud.account.id
attributes on AWS are some examples. In principle, the above considerations
apply to any resource attribute that fulfills the criteria above (not being
readily available without some extra effort that could be expensive).
Outgoing Invocations¶
This section describes outgoing FaaS invocations as they are reported by a client calling a FaaS instance.
For outgoing FaaS spans, the span kind MUST be Client.
The values reported by the client for the attributes listed below SHOULD be equal to the corresponding FaaS resource attributes and Cloud resource attributes, which the invoked FaaS instance reports about itself, if it's instrumented.
| Attribute | Type | Description | Examples | Requirement Level |
|---|---|---|---|---|
faas.invoked_name |
string | The name of the invoked function. [1] | my-function |
Required |
faas.invoked_provider |
string | The cloud provider of the invoked function. [2] | alibaba_cloud |
Required |
faas.invoked_region |
string | The cloud region of the invoked function. [3] | eu-central-1 |
Conditionally Required: [4] |
[1]: SHOULD be equal to the faas.name resource attribute of the invoked
function.
[2]: SHOULD be equal to the cloud.provider resource attribute of the
invoked function.
[3]: SHOULD be equal to the cloud.region resource attribute of the invoked
function.
[4]: For some cloud providers, like AWS or GCP, the region in which a
function is hosted is essential to uniquely identify the function and also part
of its endpoint. Since it's part of the endpoint being called, the region is
always known to clients. In these cases, faas.invoked_region MUST be set
accordingly. If the region is unknown to the client or not required for
identifying the invoked function, setting faas.invoked_region is optional.
faas.invoked_provider 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 |
|---|---|
alibaba_cloud |
Alibaba Cloud |
aws |
Amazon Web Services |
azure |
Microsoft Azure |
gcp |
Google Cloud Platform |
tencent_cloud |
Tencent Cloud |
Function Trigger Type¶
This section describes how to handle the span creation and additional attributes
based on the value of the attribute faas.trigger.
Datasource¶
A datasource function is triggered as a response to some data source operation
such as a database or filesystem read/write. FaaS instrumentations that produce
faas spans with trigger datasource, SHOULD use the following set of
attributes.
| Attribute | Type | Description | Examples | Requirement Level |
|---|---|---|---|---|
faas.document.collection |
string | The name of the source on which the triggering operation was performed. For example, in Cloud Storage or S3 corresponds to the bucket name, and in Cosmos DB to the database name. | myBucketName; myDbName |
Required |
faas.document.operation |
string | Describes the type of the operation that was performed on the data. | insert |
Required |
faas.document.time |
string | A string containing the time when the data was accessed in the ISO 8601 format expressed in UTC. | 2020-01-23T13:47:06Z |
Recommended |
faas.document.name |
string | The document name/table subjected to the operation. For example, in Cloud Storage or S3 is the name of the file, and in Cosmos DB the table name. | myFile.txt; myTableName |
Recommended |
faas.document.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 |
|---|---|
insert |
When a new object is created. |
edit |
When an object is modified. |
delete |
When an object is deleted. |
HTTP¶
The function responsibility is to provide an answer to an inbound HTTP request.
The faas span SHOULD follow the recommendations described in the
HTTP Server semantic conventions.
PubSub¶
A function is set to be executed when messages are sent to a messaging system.
In this case, multiple messages could be batch and forwarded at once to the same
function invocation. Therefore, a different root span of type faas MUST be
created for each message processed by the function, following the
Messaging systems semantic conventions. This way, it is possible
to correlate each individual message with its invocation sender.
Timer¶
A function is scheduled to be executed regularly. The following additional attributes are recommended.
| Attribute | Type | Description | Examples | Requirement Level |
|---|---|---|---|---|
faas.time |
string | A string containing the function invocation time in the ISO 8601 format expressed in UTC. | 2020-01-23T13:47:06Z |
Recommended |
faas.cron |
string | A string containing the schedule period as Cron Expression. | 0/5 * * * ? * |
Recommended |
Other¶
Function as a Service offers such flexibility that it is not possible to fully
cover with semantic conventions. When a function does not satisfy any of the
aforementioned cases, a span MUST set the attribute faas.trigger to "other".
In this case, it is responsibility of the framework or instrumentation library
to define the most appropriate attributes.
Example¶
This example shows the FaaS attributes for a (non-FaaS) process hosted on Google
Cloud Platform (Span A with kind Client), which invokes a Lambda function
called "my-lambda-function" in Amazon Web Services (Span B with kind Server).
| Attribute Kind | Attribute | Span A (Client, GCP) | Span B (Server, AWS Lambda) |
|---|---|---|---|
| Resource | cloud.provider |
"gcp" |
"aws" |
| Resource | cloud.region |
"europe-west3" |
"eu-central-1" |
| Span | faas.invoked_name |
"my-lambda-function" |
n/a |
| Span | faas.invoked_provider |
"aws" |
n/a |
| Span | faas.invoked_region |
"eu-central-1" |
n/a |
| Span | faas.trigger |
n/a | "http" |
| Span | faas.invocation_id |
n/a | "af9d5aa4-a685-4c5f-a22b-444f80b3cc28" |
| Span | faas.coldstart |
n/a | true |
| Resource | faas.name |
n/a | "my-lambda-function" |
| Resource | faas.version |
n/a | "semver:2.0.0" |
| Resource | faas.instance |
n/a | "my-lambda-function:instance-0001" |
| Resource | cloud.resource_id |
n/a | "arn:aws:lambda:us-west-2:123456789012:function:my-lambda-function" |